Growing onions in a minimum tillage system would drastically reduce the negative economic and environmental consequences of erosion, while sustaining long-term production of onions grown on muck soils. A study conducted in 2008 showed that a minimum tillage systems using fall-planted winter wheat and spring oats as inter-row cover crops in direct seeded onions had a lot of promise. In this project, critical improvements to these systems necessary for grower adoption were studied. A 1.5-fold increase in the rate of spring barley to 75 lbs/acre (in place of oats) planted in the fall resulted in a 3- and 5-fold increase in ground cover and cover crop residue, respectively, and thus, acceptable protection from soil erosion.
Instead of applying phosphorous and potassium in the fall prior to seeding the cover crops and relying on side-dressing nitrogen during the spring as was done in 2008, in this study, applying NPK in the spring, followed by shallow incorporation with a multivator between the cover crop rows proved to be very effective. Growing onions in a minimum tillage system with a spring barley inter-row cover crop resulted in an above average yield of 509 and 492 cwt/A for Festival and Safrane varieties, respectively, and with 79% and 97% of the total weight falling into the higher priced medium and jumbo size bulb classes, the barley minimum tillage system had the highest economic return.
The cost of establishing this minimum tillage system was only two-thirds the cost of establishing onions conventionally, and required 3 fewer passes across the field. This study proved that when winter wheat was used as an inter-row cover crop that the resulting stand reduction was caused by either allelopathy or another crop inhibition mechanism, and that it was not caused by damping off pathogens. Consequently, spring-killed winter wheat should not be used as an inter-row cover crop in a minimum tillage system for direct seeded onions grown on muck soil.
Available nitrogen ranged from 1.4- to 5-fold higher in the minimum tillage systems throughout the growing season. The decomposing cover crops mineralized an estimated 20 to 25 lb/A of nitrogen, some of which became available to the onion crop during the season. The shallow depth of fertilizer incorporation of NPK in the minimum tillage systems also appeared to increase nutrient availability. Thus, there seems to be potential to reduce fertilizer rates when onions are grown in a minimum tillage system, the dynamics of which warrant further study. It appears that growing direct seeded onions in a minimum tillage systems with a spring barley inter-row cover crop on muck soil is a viable practice that growers can adopt to preserve nonrenewable muck soils and to reduce environmental pollution.
We observed three onion farmers who have adopted minimum till in muck soils and who have reduced their fertilizer rates. They have seen decreased disease and increased yields.
Results have been presented in Michigan at the Great Lakes Fruit, Vegetable and Farm Markets Expo, December 2012, an article was published in “The Grower”, and this project was featured in the national 2011-1012 SARE Report from the Field.
The challenge with using conventional tillage practices for onion production on muck soils is that it results in the subsidence of muck via wind and water erosion at a rate of one foot every 10 years, which is not sustainable for preserving these non-renewable natural resources for long-term productivity. Eroded muck contains nitrogen and phosphorous fertilizers, which pollute waterways.
New York is the largest producer of onions in the Northeastern U.S. accounting for 97% of the production, with approximately 10,000 acres and an annual average value of 51.8 million dollars. Approximately 80% of the onions are grown on muck soils. Muck or organic soil is defined as one that contains more than 20% organic matter and can have 80% or more organic matter. Muck soils are non-renewable resources that were developed underwater by many generations of plants that were preserved under anaerobic conditions. It takes nature about 500 years to accumulate one foot of muck soil.
Muck soils are highly productive with excellent water-holding capacity and are used extensively for vegetable production, especially onions. Onions produced on muck soils are of superior quality compared to onions grown on mineral soil, because the high sulfur content of muck improves onion flavor, cooking quality and storability.
Unfortunately, muck soils are prone to subsidence, which is the permanent lowering of the surface elevation, a phenomenon resulting from the oxidation of soil organic matter by aerobic microorganisms, and by wind and water erosion. An estimated rate of soil subsidence on intensively cropped muck soil is one foot every 10 years. As much as one inch of muck can be eroded during a severe wind storm when dry muck soil is exposed to the elements. Drainage ditches can be filled in and onion seedlings can be decapitated, severely damaged, uprooted or buried during high winds. For example, in spring of 2009, despite traditional wind erosion prevention techniques (i.e. willow windbreaks and barley nurse crops seeded between onion rows), three high wind events resulted in at least 600 acres of the 3000 acres of onions grown on the Elba muck land having had to be replanted at an expense of $700 to $800 per acre. Additionally, these later planted fields never reached their full yield potential and were of inferior quality, costing growers additional hundreds of dollars per acre in lost yields and quality.
A water monitoring project conducted by the Soil and Water Conservation District of Orleans County and SUNY Brockport in 2008-2009 identified the Elba muck land as a major source of nutrient loading into the Oak Orchard water shed with excessive levels of total and soluble reactive phosphorous, and total and soluble nitrate. Waterways are certain to be polluted when spring wind storms erode freshly fertilized muck into drainage ditches. Clearly, sustainable onion production practices are absolutely warranted.
It is scientifically proven that erosion and subsidence decrease as ground cover increases and cultivation decreases. Therefore, growing onions in a minimum tillage system would drastically reduce the negative economic and environmental consequences of erosion, while sustaining long-term production of onions on muck soils.
In 2007, we had a NESARE Partnership grant (ONE07-072) where we evaluated growing onions in minimum tillage (MT) production systems on muck soil on a commercial scale. For this project, the grower cooperator direct seeded onions between rows of fall-planted cover crops, winter wheat and spring oats. This project was the first of its kind and demonstrated that producing onions in a MT system had great potential. The MT systems yielded the same as the conventional system, and had significant reductions in erosion, soil compaction and pest pressure including onion thrips, bacterial disease and Botrytis leaf blight.
In our first attempt, the oat cover crop was too thin and gave us only 10% ground cover at planting. In this project, we continued to investigate using a cover crop that is winter killed and one that is spring killed, with the goal of each providing about 50% ground cover at planting.
In our first attempt, our techniques for applying fertilizer were inefficient. The full rate of nitrogen-phosphorous-potassium (NPK) fertilizer was applied in the fall. The following spring, pop-up fertilizer was applied in-furrow and urea was applied broadcast and rained in twice. Consequently, soil P was low, because a portion was lost over winter, and soil nitrate-N levels were low until mid-June. In this project, the grower cooperator applied the full rate of NPK in the spring prior to seeding by broadcasting and incorporating it between the cover crop rows.
We wanted to investigate banding fertilizer below the seed as an alternative to broadcasting and incorporating it in minimum tillage systems. When fertilizer is banded, rates may be reduced because it is located where it is most available to the plants, resulting in potential savings on fertilizer costs and reduced water pollution. In this study, we wanted to investigate banding P and K below the seed in a MT system.
In the MT wheat system, there was a release of nutrients when the residue broke down that was taken up by the onions. This is an important dynamic that was studied in this project, because it could impact fertilizer rates, onion maturity and susceptibility to pests.
Since the onions grown in the MT oats system yielded the same as those grown conventionally despite having only half as much available nitrogen, we wanted to investigate the feasibility of growing onions with lower rates of NPK.
In the MT wheat system, there was a 50% stand reduction, because the wheat residue provided ideal conditions for damping off pathogens to kill seedlings. In this project, we evaluated commercially available fungicides for their ability to control damping off.
The purpose of this project was to continue our progress towards developing a minimum tillage system for direct seeded onions grown on muck soil. Specifically, our objectives were to:
This objective was partially met. Our goal was to achieve approximately 50% ground cover with both a fall and a spring-killed cover crop by mid-May. Although we had less than 50% ground cover for both fall and spring-killed cover crops, we had more uniform coverage between the two cover crops (fall – 19%; spring – 25%) than we did in the first year of study (fall – 10%; spring – 60%).
This objective was partially met. Timing of fertilizer application and incorporation in the spring was completed successfully and proved to be a successful and practical technique. Our plan was to evaluate three tillage systems in three varieties, but due to an abnormally wet and cold April and May in 2011, the stand establishment in the third variety was only 25%, so it was abandoned. We also set up a small-scale small-plot trial to investigate banding P and K below the seed. Unfortunately, applying fertilizer in a band below the seed proved impossible with our modified push seeder, because with minimum tillage the ground was simply too hard to push the seeder through the soil. Instead, a reduced fertilizer rate study was set up with 50%, 75% and 100% of the recommended rates of NPK. Again, due to an abnormally very wet and cold spring, we had very poor stand establishment (~33%) in this trial, and it too, had to be abandoned. Although we got some interesting results pertaining to the dynamics of nutrient availability when using inter-row cover crops, further study is warranted to understand this completely.
This objective was partially met. A small-plot trial was successfully established within the MT wheat system where damping off pressure was expected to be the highest to evaluate fungicide seed treatments to control damping off. We got no significant differences among treatments. Instead, we were able to conclude that damping off was in fact not the cause of reduced stand in the MT wheat system. Rather, our results strongly suggest that the use of a spring-killed winter wheat inter-row cover crop has either allelopathic or other crop inhibition effects on onion germination.
In this project, we evaluated and demonstrated critical improvements required for adoption of growing direct seeded onions in a minimum tillage system on muck soil on a commercial scale.
A 30 acre field of muck land was dedicated to this project. After harvesting onions, plowing and fitting a field, on September 15, 2010, the grower cooperator drilled 50 lb/A and 75 lb/A of cover crops, winter wheat and spring barley, respectively, into 10.5 inch rows, which were spring and winter killed, respectively. Minimum tillage (MT) wheat, MT barley and the conventional planting systems were alternated in 15 foot wide passes (= 3 x 5 foot beds, 5 rows spaced 10.5 inch per bed) across the field with every other pass being MT wheat, and the passes in between alternating between conventional and MT barley (Figure 1). On April 4, 2011, Roundup was applied at 1.5 pt/A to the winter wheat, which was 6-8 inches tall. The conventional strips were disked.
Fertilizer was applied according to Cornell recommendations that were based on a soil test. A composite soil sample was collected from the entire field on April 12, 2011 and sent to the Cornell Nutrient Analysis Laboratory (CNAL). On April 15, 2011, 480 lb per acre of 16-31-11 NPK (= 76.8 lb N, 149 lb P and 53 lb K) was applied broadcast on the entire field. In the conventional systems, NPK was incorporated using a culti-mulcher. In the MT sections, NPK was incorporated using a multivator between the cover crop rows to disturb the ground cover as minimally as possible. Figure 2 and
3 show each of the tillage systems prior to planting.
In the conventional strips, barley was seeded in 10.5 inch rows at 65 lb per acre to serve as a nurse crop for wind protection on April 16, 2011. The field was divided into three equal 10 acre sections, each of a different variety of yellow storage onions including Festival, Safrane and Patterson. Due to the extremely wet April, the entire field could not be planted in one day: Festival was planted on April 24, 2011, Safrane on April 17, 2011, and Patterson was planted on April 30, 2011. Unfortunately, Patterson was also in a wetter section of the field and stands were very poor (~25%) and had to be abandoned. All tillage systems were seeded using a 15-row Monosem onion seeder with wavy coulters mounted on the front before the press wheel (Figure 4). Auto-steering and global positioning system (GPS) were used to plant the cover crops in the fall and again to plant the onions precisely between the cover crop rows in the spring, which were also spaced 10.5 inches apart. Onions were planted at 7 seeds per foot for a target plant population of 348,480 plants per acre. At planting, 5 gal per acre of 6-24-6 NPK was applied in-furrow at planting in all systems. On July 12, 2011, 100 lbs of urea (46-0-0 NPK) was applied broadcast and left to be naturally rained in. In general, stands were mediocre with some areas having excellent stands. To overcome such variability, data was collected from multiple sub-samples per replicate.
The grower cooperator managed all sections of the field exactly the same with respect to pest management. In the conventional strips, killing the barley was delayed due to wet field conditions and it was greater than 6 inches tall and tillering. Ideally, barley is killed when the onions are at the 1-2 leaf stage and when it is 4-6 inches tall. This created more competition and more residue in the conventional system than what would be considered normal.
Each variety was evaluated separately and divided into 5 replicates. Unless otherwise stated, data was collected from 2 sub-samples per replicate.
Ground cover – was estimated visually and by harvesting the above-ground residue in 5 ft x 5 ft sub-sample areas, which was oven-dried to obtain dry weight, on May 10, June 15 and September 9. On May 10, randomly selected sub-samples were collected per replicate across all varieties. Residue samples for dry weight analysis were collected in a similar fashion on June 15. It was originally planned to collect ground cover residue samples monthly, but this proved also to be too time consuming.
Stand establishment – As planned, in each sub-sample, the number of plants emerged per 3 feet of row for each of the 5 rows per bed were counted at the first true leaf stage on June 3 and at the 3-5 leaf stage on June 29. A final stand was calculated based on the number of bulbs harvested per 25 feet of row (5 ft in each of 5 rows per bed) on September 13 and 14.
Fertility – A composite soil sample was collected per replicate per tillage system per variety at the 4 leaf stage on Jun 30, which was submitted to CNAL for complete nutrient analysis. Composite soil samples for available nitrate were collected in the same manner as described for the complete nutrient analysis tests on June 14, July 8 and August 5 at the 2, 5 and 9 leaf stages, respectively. Samples were kept cool in the field and dried completely in a microwave oven within 12 hours of collection. Available nitrate-nitrogen (N-NO3) was evaluated using a compact nitrate meter (Horibia B-343). For each sub-sample, two samples were prepared and available N-NO3 measured in ppm. In muck soil, 1 ppm is equal to 1 lb/A, because muck soil is half as dense as mineral soil, where ppm is typically converted to lb/A by multiplying by a factor of 2. Also, on August 5, the inner four leaves of 10 randomly selected plants per replicate per system per variety were collected and sent to CNAL for plant tissue analysis of total nitrogen.
Plant size – On 10 randomly selected plants per sub-sample, number of leaves per plant and height of the tallest leaf per plant were measured on June 29, July 15-16 and August 11-12. Neck diameter was measured on August 11-12.
Pest pressure – On July 15-16 and August 11-12, number of onion thrips per plant and Botrytis leaf blight lesions per outer 3 leaves per plant were counted on 10 and 6 randomly selected plants per sub-sample, respectively.
Soil temperature and moisture – were not measured, because our data loggers were in use for another project.
Yield and grade – On September 13 and 14, all of the onions in two sub-sample areas of 5 feet x 5 feet were pulled, topped, weighed and graded according to size ; jumbo (2-3 inch), medium (1.25-2 inch), small (0.75-1.25 inch) and boliers (<1.75 inch).
We wanted to evaluate whether banding fertilizer below the seed was a feasible strategy to reduce fertilizer rates within a minimum tillage system. The treatments were to include: 1) 100% NPK broadcast, 2) 100% NPK banded and, 3) 75% NPK banded for a total of 9 treatments. Rates of P and K were according to Cornell recommendations based on a CNAL soil test (taken on April 12, 2011 from entire field). The 100% rate of P and K were 150 lb and 50 lb per acre, respectively. The 100% rate of N was 100 lb/A. For the banded treatments, up to 100 lb of P and up to 80 lb of K + N per acre were to be applied in a band while the remaining NPK was to be broadcast.
This trial was set up as a small-plot trial with 5 replications within the large minimum tillage field. The grower left an area that was 9 beds wide with 3 beds for each tillage system by 420 feet long. Each treatment-replicate consisted of 1 bed wide (5 feet with 5 rows of onions) in the center bed of the 3 per tillage system by 20 feet long. A 5-foot buffer was left on the end of each plot. Broadcast applications were weighed out per treatment-replicate, spread by hand and incorporated with a hoe in the conventional treatment. In the MT treatments, the fertilizer was left on the soil surface. Banded fertilizer applications were to be made using a push seeder with a modified shoe to deliver fertilizer 3-4” deep. Unfortunately, without fitting the ground in the spring, it was too hard for our push seeder to deliver the fertilizer in bands 3-4 inches deep. Instead of evaluating banding, we set up a trial on May 5 to evaluate reduced fertilizer rates with only broadcasted applications of 100%, 75% and 50% NPK. Figure 5 illustrates the set-up of this trial. The grower planted the onions in the entire trial area with the variety, Festival on May 6. Unfortunately, the stand establishment in this trial was very poor (~33%), so this trial had to be abandoned.
Commercially available seed treatments, Pro Gro, Farmore D300, and the exclusive package for Nunhem’s onion varieties consisting of Pro Gro + Coronet + Allegiance were evaluated with and without Ridomil applied as an in-furrow treatment, for a total of six treatments were evaluated. All treatments included Pro Gro and Manzate, which was applied in-furrow, for protection against the soil borne disease, onion smut. Also, all treatments included Sepresto seed treatment for control of onion maggot. The complete treatment list is detailed in Table 2. The commercially treated seed (cv. Infinity) was provided to us by Nunhem’s Seed Company. The trial was set up as a small-plot randomized complete block design with 5 replications within one of the MT wheat systems. Each treatment-replicate consisted of a single 20 foot row. The trial was planted with a cone push seeder on May 9. Stand counts were taken weekly from loop- to 2-leaf stages on May 25, June 2, June 9 and June 15. All of the remaining onions were pulled out of the field on September 9, windrowed, and then topped and weighed on October 12.
Statistical differences among treatments was determined by General Analysis of Variance (ANOVA) with mean separation by Fisher’s Protected LSD test, ? = 0.05.
To determine the cost of establishing minimum tillage systems, the cost of cover crop seed, herbicides to kill the cover crops when applicable, fuel and labor were considered. An average cost of $15 per acre for fuel and labor was used for each pass across the field to plow, apply fertilizer, plant seed, etc. Cost of fertilizer and maintenance was not included as they were assumed to be exactly the same for each tillage system. Profit was determined using the yield data from the trial, and the average onion prices per bulb size class, provided by the grower cooperator. Net return was the total profit minus the cost of establishing each tillage system.
Prior to planting on April 15, the MT wheat and barley systems had approximately 50% and 30% ground coverage, respectively, compared to the conventional system, which had 0% (Figure 2 and 3). We succeeded in increasing the ground coverage of the winter-killed cover crop from our first attempt in 2008, when we only had 10% ground cover in the spring, which did not appear to be enough for suitable wind protection. Prior to spring killing, the winter wheat had slightly less ground cover in 2011 (50%) than it did in our first attempt in 2008 (60%). In our previous study, the heavy ground cover of winter wheat caused wet and cool soil conditions that resulted in poor stand establishment. By May 10, 2011, after planting, the winter wheat residue was reduced by half to 26%, and the barley residue was reduced by about a third to 19% (Figure 6). Part of the loss in ground cover was due to the cultivating activity between the cover crop rows to incorporate the fertilizer prior to planting. On May 10, in the conventional system, the newly seeded barley nurse crop covered only 11% of the ground; the MT systems with wheat and barley had significantly 2.3x and 1.7x more ground cover than the conventional system (Figure 6). The MT wheat system had significantly the highest weight of plant residue on May 10, which was 40 times higher than the conventional system. The MT barley system had significantly 29x more plant residue than the conventional system (Figure 6). It is during this critical 4-6 week period from early April until mid-May when the cover crops in the MT systems provide superior protection against erosion compared to the conventional system where the muck soil is unprotected.
The MT wheat system also had significantly the highest plant residue on June 15 and September 13-14. On June 15, in the conventional system, the weight of plant residue from the barely nurse crop (135 g/25 ft2) increased 16-fold from May 10 (8.6 g/25 ft2) and was not significantly different than the MT barley, but the spring-killed wheat in the MT system was still 3-fold more than the barley in the conventional system. Ground cover was relatively constant between May 10 and September 9 in in the MT wheat system, whereas it increased 2.5-fold in the conventional system and decreased by 75% on the MT barley system during the same time period. The MT barley system ended up having significantly one quarter of the plant residue weight of the conventional system at harvest, while the MT wheat system had significantly twice the plant residue weight. Figure 7 shows the amount of ground cover left from the cover crops at harvest.
At harvest, there was a significant tillage system by variety interaction for both ground cover and dry weight of cover crop residue. When the varieties were pooled across tillage types, Festival had numerically slightly higher ground coverage by 3.7% and significantly more plant residue weight by 20 g/25ft2. In Festival, the MT wheat had significantly 1.4 times more ground cover than the conventional, which had significantly 4.3 times more ground cover than MT barley. In Safrane, the conventional had significantly 1.5 times more ground cover than the MT wheat, which was significantly 4.6 times more ground cover than MT barley. The trends were the same for the dry weight of cover crop residue among tillage types in each variety, being that MT wheat had the highest weight, which was significantly higher than the conventional, which was significantly higher than the MT barley. The difference was that the dry weight of cover crop in the MT wheat in the Festival variety was double of what it was in Safrane.
Compared to the 2008 study, in this study, there was 5 times as much cover crop residue measured in dry weight in mid-June (June 15, 2011 vs. June 19, 2008) of the barley nurse crop in the conventional system (2008: 11.5 g/m2; 2011: 58 g/m2) and 5 times as much cover crop in the MT barley system (2008: 12.7 g/m2 of oats; 2011: 65 g.m2 of barley), while the amount of residue in the MT wheat system was very similar (2008: 183 g/m2; 2011: 173 g/m2). In 2008, by July 30, the conventional system had 0% ground cover. The difference between the 2008 and the 2011 trials is that the nurse barley crop in the conventional system did not get killed on time in 2011, which would ideally occur at the 1-2 leaf stage before the barley starts to tiller. Although the barley was killed when the onions were at the 1 leaf stage on May 10 in 2011, the barley was already 6-8 inches tall and tillering because, the cool wet spring delayed the emergence and growth of the onions making the barley nurse crop much ahead of the onions. Figure 8 shows how big the nurse barley crop was just two weeks after herbicides were applied to kill it. Untimely kill of a barley nurse crop can result in stunted onion growth due to competition for sunlight and nutrients, and increased onion seedling death due to heat stress, because the nurse crop holds in heat and draws moisture from the onion seedlings.
It is unknown why there was more cover crop residue in the MT wheat system in the Festival variety compared to Safrane. It may be due to the section of the field where Safrane was planted being drier ground, which could result in warmer soil temperatures and more rapid kill of the cover crop with Roundup and then decomposition by soil microbes.
A significant interaction between tillage type and variety occurred for stand on June 3 and at harvest; stand data was only collected from the Festival variety on June 29. At the first leaf stage on June 3, the variety Festival had significantly greater stand than the variety Safrane by 0.8 seeds per foot, which represented 77% and 65% of the planted plant population for Festival and Safrane, respectively. At the first leaf stage, both varieties responded similarly to tillage type for stand. When pooled across varieties, the conventional and MT barley systems had significantly 1.5x and 1.2x more plants per foot than the MT wheat, respectively, which represented 80%, 58% and 76% of the planted plant population for conventional, MT wheat and MT barley, respectively. At the 3-4 leaf stage on June 29, the same trend that was established at the first leaf stage in Festival was still present, only total stand was lower by 1.0 plants per foot in the conventional and by 0.5 plants per foot in the two MT systems, representing 74%, 51% and 74% of the planted plant population for conventional, MT wheat and MT barley, respectively. At harvest in the Festival variety, the final stand in MT wheat was 2.4 plants per foot (=34% of the planted plant population), which was significantly less than the conventional by 2.1 seeds per foot (=64% of the planted plant population) and MT barley by 2.1 plants per foot (=64% of the planted plant population). Figure 7 shows the reduced plant population in the MT wheat system compared to the conventional at harvest. In the Safrane variety, there were no significant differences in final stand among tillage types.
The 50% stand loss in MT wheat compared to the conventional and MT barley in the Festival variety could be a function of the higher ground cover in this treatment compared to the Safrane variety. For ground cover, we only collected data for each variety separately at harvest. At this time, the conventional and MT barley treatments in the two varieties had similar ground cover (conventional – Festival: 25%; Safrane: 30%; MT-barley – Festival: 6%; Safrane – 4%) and cover crop dry weight (conventional – Festival: 44 g/25ft2; Safrane: 41 g/25ft2; MT barley – Festival: 9 g/25ft2; Safrane: 12 g/25ft2), while the MT wheat had 34% ground cover and 113 g/25ft2 dry weight of cover crop residue in Festival and only 20% ground cover and 53 g/25ft2 dry weight of cover crop in Safrane (Table 3). In 2008, the stand on July 31 in the MT wheat system was also 50% of the conventional and MT oats system, while ground cover was 30% in the MT wheat, 0.5% in the MT oats and 0% in the conventional. In 2008, dry weight of the cover crop on June 19 in MT wheat was 448 g/25 ft2, which was similar to the 403 g/25 ft2 of cover crop residue of MT wheat on June 14, 2011 (data collected from varieties combined). These results suggest that there may be an increased risk of onion stand reduction as winter wheat inter-row cover crop residue increases.
In 2008, we suspected that the reduction in yield in MT wheat was due to damping off, because the heavy cover crop residue kept the soil cooler and wetter than in the other systems. In the 2011 study, all of the treatments were very wet, as the weather combined for April and May of 2011 made for one of the coldest and wettest springs on record. In addition, in response to the 2008 study, in 2011 the grower used more fungicides to control damping off in the entire field, which included a higher rate of Ridomil in the furrow and adding Apron and Maxim seed treatments. In 2008, seed was treated with just Pro Gro, and mancozeb and a low rate of Ridomil was used in the furrow. Since the MT wheat treatment again had a 50% reduction in stand compared to conventional and MT barley treatments despite all treatments being very cold and wet and having fungicides to control damping off, the reduction in stand must have been caused by something other than damping off.
One possibility is that the wheat inter-row cover crop was allelopathic to the onions. Allelopathy is the inhibition of growth in one species of plants by chemicals produced by another species. In Georgia, wheat straw mulch applied to sweet onions for weed management in an organic system demonstrated some allelopathic effects resulting in stand loss. In a study in China, germination of crab grass was inhibited more by extracts of winter wheat from the shoots than roots, and from the extracts of young wheat seedlings than mature wheat plants (Li et al. 2005). If this is also true for the allelopathic effects of wheat against onions, than the decaying shoots of wheat seedlings in between the onion rows could be especially detrimental to germinating onion seedlings. In cool and wet soil conditions, allelopathic chemicals are expected to break down slower. Greatest stand loss occurred in the MT wheat system in the Festival variety, which was on wetter ground and had higher cover crop residue than in the Safrane variety.
According to Cornell Cover Crops Specialist, Thomas Bjorkman, he has consistently seen “crop inhibition” following wheat, although not in onions, specifically. He believes that the wheat cover crop promotes the proliferation of soil microbes or insects, such as seed corn maggot, that weakens the crop plants. In our study, since we effectively ruled out damping off pathogens as the cause of reduced stand and since we evaluated nine active ingredients belonging to five different fungicide classes, applied at planting and saw no improved stand, it can be concluded that there are no fungicides that onion growers can use to combat the soil microbes that may be causing reduced stand in a minimum tillage system where winter wheat is used as an inter-row cover crop. No seed maggot problems were observed in either the 2008 or 2011 study. It is common practice in direct seeded onions grown in muck soils that insecticides effective in controlling seed maggots are applied as seed and in-furrow treatments, thus, seed maggot issues is a low concern for onions grown in a minimum tillage system.
pH and %OM: In the trial, pH ranged from 5.0 to 5.1 and percent organic matter (% OM) ranged from 50 to 55%, which is representative of high quality muck soil. There were no differences in pH and % OM among treatments except that pH was significantly 0.1 unit higher where the Festival variety was grown compared to the Safrane variety, and in the Safrane variety, % OM was significantly 2% lower in the conventional than in the MT systems. In the Festival variety, % OM in the conventional system was numerically 8% higher than it was in the MT system.
Available nitrogen: The soil levels of nitrogen ranged from 21 to 61 lb/A on July 8 and were slightly high. In an early Cornell study, a 450 cwt/A onion crop grown on muck used an average of 75 lb/A of nitrogen, so in this study, there was 28 to 81% of the required nitrogen available when the crop was 60% complete. When pooled across tillage systems, there were no significant differences between varieties, except at the 5 leaf stage on July 8 when Safrane had significantly higher available nitrate-N than Festival by 10 lb per acre. In general, when pooled across varieties, the MT systems had significantly 5x, 2x and 1.4-1.6x more available nitrate-N than the conventional at the 2-, 5- and 9-leaf stages, respectively. In the conventional system, available nitrate-N increased from 5 lb/A at the 2 leaf stage (June 14) to 23 lb/A at the 5 leaf stage (July 8) and to 32 lb/A at the 9 leaf stage (August 5). In the MT systems, available nitrate-N increased from 27 and 28 lb/A at the 2 leaf stage to 49 and 47 lb/A at the 5 leaf stage and remained fairly stable at 49 and 44 lb/A at the 9 leaf stage for the wheat and barley MT systems, respectively. A significant variety by tillage type interaction occurred on July 8. In the Festival variety, MT wheat had significantly 1.5x and numerically 1.3x more available nitrate-N than MT barley at the 5 leaf and 9 leaf stages, respectively. In Safrane, in MT barley, available nitrate-N decreased 14 lb/A from the 5- to the 9-leaf stages, and was 1.3x higher than MT wheat at the 5 leaf stage.
Although actual levels of available nitrate-N in the MT systems were similar between 2008 and 2011, our finding in 2011 that the levels of available N in the MT systems were higher than in the conventional was opposite to our previous findings. In 2008, on June 19 at the 4-leaf stage, just 6 days after the second side-dress application of nitrogen for a total of 151 lb/A of applied nitrogen, the conventional system had 74 lb/A of available nitrate-N, compared to 23.5 lb and 36.5 lb/A in the MT oats and wheat systems, respectively. In 2008, in the conventional system, 98 lb/A of N was applied broadcast and then incorporated prior to planting in the spring and was followed by a side dressing of 23 lb/A N which was broadcast and left on the soil surface to be naturally rained in. In the MT systems, 56 lb/A of N was applied in the fall prior to planting the cover crop, and then two applications of 46 lb/A of N were side-dressed and left on the surface to be naturally rained in. Perhaps, the cool and wet spring in 2011 may have resulted in leaching and slowed availability of N in the conventional compared to 2008. In addition, some of the applied N may have been used up by the barley nurse crop, which got too big before it was killed. In 2011, daytime temperatures warmed up into the 80s starting May 20 and the soil did not begin to dry out until after June 20. The increase in available nitrogen on July 8 and August 5 could reflect the increased availability from at planting and side-dress fertilizer applications (which could have been naturally rained in on July 26) and from being released from the decaying barley nurse cover crop, which was killed on May 20. Unfortunately in 2008, available nitrate-N was not measured beyond June 19, so we cannot compare whether an increase in available N occurred as the season progressed as we saw in 2011.
It is likely that some of the available N in the MT systems was released from the decomposing cover crops. When crop residue has a higher carbon: nitrogen (C:N) ratio than 24:1, which is the perfectly balanced diet soil microorganisms require, the microbes will consume the cover crop and leave the excess nitrogen in the soil, leaving a surplus in the soil for other microbes and plants to use. The C:N ratio of wheat and barley that is spring killed is approximately 16:1 and would contain approximately 2% N, which with the amount of cover residue in our study on May 10 (MT wheat – 351 g/25ft2; MT barley – 253 g/25ft2) could mineralize approximately 20-25 lb/A of N. Similarly, decomposition of the barley nurse crop in the conventional system may have mineralized about 10 lb/A of N sometime after it was killed on May 20.
It is not known why the level of available nitrogen in the MT barley system was double that of the MT wheat system in the Safrane variety, when it was significantly less than that of the MT wheat in the Festival variety. On August 8, available N was again similar between the two MT systems.
Tissue analysis for N: Tissue N ranged from 3.0 to 3.5%, which according to Maynard and Hochmuth (1997) is slightly excessive; rather, sufficient range of nitrogen in onion leaf tissue is 2-3%. When pooled across tillage systems, Festival had significantly 0.3% higher tissue N than Safrane at the 9 leaf stage on August 5. When pooled across varieties, there was no difference between conventional and MT barley or between MT wheat and MT barley, but MT wheat had significantly 0.3% higher tissue N than the conventional. No significant differences in tissue N occurred among tillage systems in either variety. Numerically, MT wheat had the highest tissue N followed by MT barley and then the conventional. Figure 9 shows a side-by-side comparison of the conventional and the MT wheat in the Festival variety on July 15, where the onions in the MT wheat system visually appear greener. In 2008, at the 8-9 leaf stage on July 22, tissue nitrogen was 2.5%, 2.9% and 2.8% for the conventional, MT wheat and MT oats treatments, respectively.
In general, levels of nitrogen that occurred in the soil and leaf tissue in all treatments, but, especially in the MT treatments were generally high. This indicates that there is opportunity to reduce nitrogen fertilizer inputs, either by reducing the amount used prior to planting, or by eliminating the side dress application, or a combination of both, especially in a MT system. Further studies are warranted to ensure that this trend is repeatable. Unfortunately, our small-plot fertilizer rate trial had to be abandoned, because the stand was only 33%.
Available phosphorous (P): At the 4 leaf stage, there was no difference in available P between varieties when pooled across tillage systems. When pooled across varieties and within each variety separately, the conventional had 88 lb/A of available P, which was significantly 11 to 32 lb/A less that in the MT wheat and MT barley. According to Cornell, P levels are considered low for onions on muck when they are between 41 and 100 lb/A and medium between 101 and 160 lb/A. In this field, soil levels of P were low in the conventional system and medium in the MT systems 2 months after planting. Although not significantly different, numerically, available P followed the same trend as nitrogen with MT wheat having the higher amount in the Festival variety and MT barley having the higher amount in the Safrane variety. If the differences in P among systems are related to the fertilizer application technique, than it makes sense that soil levels of P would mimic those of N.
In the 2008 study, full rates of P and K according to a soil test were applied in the fall prior to cover crop establishment. Prior to planting in the spring, soil test results showed that levels of P were low in the minimum tillage systems (Apr 17, 2008: MT wheat – 58 lb/A P; MT oats – 47 lb/A P), which suggested that 35 to 47% of the 89 lb/A of P applied in the fall was lost over winter. For this reason, the modification was made in the 2011 study to apply NPK in the spring. Clearly, this proved to be an effective and efficient strategy. Because soil levels of P were significantly higher in the MT systems, despite all systems receiving the same amount of NPK at the same time, this suggests that either P was mineralized from the decomposing cover crops, or that the cover crops in the MT systems retained the P better than the conventional during the cool and wet May and June, or that there was a difference between fertilizer application techniques. In the conventional system, NPK was incorporated using a cultimulcher to a depth of 4 inches, and in the MT systems, NPK was incorporated using a multivator to a depth of 1-2 inches. Perhaps there is greater nutrient uptake in the MT systems, because the nutrients were concentrated in a shallower layer. To further support this theory, soil levels of P tended to mimic those of N. Alternatively, when N and P are mineralized via decomposition of cover crops, they behave very differently in the soil. In 2008, soil levels of P were not analyzed during the growing season, so it is unknown whether they increased from prior to planting to the 4-leaf stage.
Available potassium (K): Levels of K in this field all fell within Cornell’s very high range at the 4 leaf stage on June 30. When pooled across tillage systems, no differences occurred between varieties. A significant variety by interaction occurred. In both varieties, MT barley had significantly 1.3-1.5 times more available K than MT wheat and conventional. In the Festival variety, MT wheat had significantly more available K than MT barley and in Safrane, there was no difference between MT wheat and the conventional.
Available Magnesium (Mg) and Calcium (Ca): Levels of Mg and Ca that occurred in this study were typical of the levels found in the Elba muck land (Hoepting, 2009, 2010). No significant differences occurred among tillage systems for available Mg at the 4 leaf stage on June 30. Numerically, Safrane had slightly higher levels than Festival, and MT wheat had the lowest levels while the conventional had the highest. Levels of Ca tended to mimic those of Mg with MT wheat having the lowest. A significant variety by tillage system occurred for Ca. In the Festival variety, MT wheat had significantly lower available Ca than both MT barley and conventional. In Safrane, there were no significant differences among tillage types.
Available manganese (Mn): Levels of Mn were amply sufficient in the trial field and ranged from 71 to 105 lb/A; a crop response is expected to additions of Mn when soil levels are less than 9 lb per acre (Hoepting 2010). When pooled across tillage types, the Safrane variety had significantly 23 lb/A more available Mn than Festival at the 4 leaf stage on June 30. In Safrane, MT wheat had significantly 13 lb/A less available Mn than the conventional. In Festival, MT wheat also had numerically slightly lower soil levels of available Mn than the conventional and MT barley which had very similar soil levels of Mn.
Available iron (Fe), aluminum (Al) and zinc (Zn): There were no significant differences in Fe, which was consistently low at 2 lb/A, especially for the low pH of the soil. Levels of Al and Zn were normal. A significant variety by tillage type interaction occurred for Al. In Festival, MT wheat had a significantly lower level of available Al than both MT barley and conventional, which had very similar levels. In Safrane, MT barley had numerically the lowest level of available Al, while the conventional had the highest. When pooled across varieties, MT wheat had a significantly lower level of Zn than MT barley and conventional. In Festival, this also occurred, but MT barley also had significantly higher available Zn than the conventional.
Number of leaves per plant: On June 29, data was only collected from the variety Festival, in which both of the minimum tillage treatments had significantly 0.7 more leaves per plant than the conventional treatment. On July 15 and August 11-12, when pooled across tillage types, Safrane had significantly 0.7 and 0.8 more leaves per plant than Festival. On July 15, no significant differences occurred between the two minimum tillage treatments in either variety or when the varieties were pooled, which both had significantly 0.6 to 1.9 more leaves per plant than the conventional treatment. On August 11-12, a significant tillage type by variety interaction occurred. In the Festival variety, MT wheat had significantly 0.6 and 0.8 more leaves per plant than the conventional and MT barley treatments, while in the Safrane variety, MT wheat and MT barley had significantly 1.3 and 0.9 more leaves per plant than the conventional, respectively.
Plant height: On June 29, the MT barley system had the tallest plants which were significantly 2.2 inches taller than MT wheat, which had significantly taller plants than the conventional by 2.6 inches. When pooled across tillage systems, Safrane had significantly taller plants than Festival by 1.8 inches only on August 11-12. The same trend was observed on July 15 and August 11-12 in both varieties and when the varieties were pooled where there were no significant differences between tillage types, which both had significantly taller plants than the conventional by 1.4 to 3.6 inches.
Neck diameter: On August 11-12, a significant tillage type by variety interaction occurred. The Safrane variety had significantly thicker necks than Festival by 0.09 inches when pooled across tillage systems. In the Festival variety, the plants in the MT wheat had significantly thicker necks than MT barley and conventional by 0.13 and 0.12 inches, respectively. In the Safrane variety, MT wheat had plants with significantly thicker necks than the conventional by 0.06 inches, while there were no significant differences between the two MT systems.
The larger plants in the minimum tillage systems may be due to the higher availability of N and P compared to the conventional. Thick onion stands can yield taller onion plants which mature earlier, while thinned stands can yield onion plants with more leaves and delayed maturity. In this study, despite a significant stand reduction in the MT wheat in the Festival variety, plants were similar in size to the plants in the MT barley system, except for having significantly thicker necks. In this trial, there were patches of stunted onions throughout the conventional plots (Figure 9) with often only 1 or 2 rows per bed affected while onions in adjacent rows appeared normal. When a barley nurse crop gets too big before it is killed, as was the case in this study, it can stunt the onions, but there did not appear to be a pattern between the amount of barley nurse crop and onion stunting. Unfortunately, soil tests or compaction tests from the stunted and normal looking plants were not taken. The stunting occurred throughout the duration of the trial and its cause remained unknown.
Botrytis leaf blight (BLB): On July 15-16 at the 6-7 leaf stage, when pooled across tillage types, the Safrane variety had significantly 0.6 more BLB lesions per leaf than Festival. When pooled across varieties and in the Festival variety, the plants in the MT wheat system had significantly 0.6 to 1.4 more BLB lesions per leaf than both the plants in the MT barley and conventional systems. There were no significant differences in the Safrane variety. On August 11-12 at the 8-9 leaf stage, BLB levels dropped from the July 15-16 assessment, which is typical, because hot and dry summer conditions and more mature plants are not conducive to BLB. A significant variety by tillage interaction occurred. Significant differences only occurred in the Safrane variety, where the plants in the MT wheat and conventional systems had 0.7 and 0.9 more BLB lesions per leaf, respectively, than the MT barley system. In the Festival variety, both of the MT systems had numerically higher levels of BLB than the conventional system. No differences in BLB occurred between the two varieties on August 11-12. In 2008, onions in the MT wheat system had significantly less BLB than the other treatments. Although significant differences occurred, with inconsistencies among these differences and relatively low disease pressure, it was not possible to determine whether a change in BLB pressure would be expected when switching to a minimum tillage system from conventional.
Onion thrips (OT): On July 15-16 at the 6-7 leaf stage, there were no differences in OT pressure between varieties, although numerically they were slightly higher in Safrane. In the Festival variety, OT were significantly 1.7 and 2.3 OT per leaf higher in the MT barley system than MT wheat and conventional, respectively, which were not significantly different from each other. In Safrane, the MT barley system had 4.3 OT per leaf, which was significantly 1.4 and 3.5 OT per leaf higher than MT wheat and the conventional. The conventional system had significantly lower incidence of OT than the other treatments. This pattern was similar to when the varieties were pooled across tillage treatments. On August 11-12 at the 8-9 leaf stage, levels of OT had dropped to about one third of the July 15-16 levels. Generally, OT pressure increases as the growing season progresses until the plants begin to lodge when the OT move out of the plants. A significant variety by tillage type interaction occurred. The Safrane variety had significantly 0.4 OT per leaf higher OT than Festival. In Festival, the plants in the conventional and MT wheat systems had significantly about twice as many OT as the plants in the MT barley system. In Safrane, the MT wheat and barley systems had significantly about one third as many OT as the conventional system.
On July 15-16, the onions in the MT barley system clearly had significantly more OT than the other systems. In 2008, on July 31, the MT oat system had significantly lower OT than the conventional and MT wheat systems, and both of the MT systems had significantly lower OT than the conventional on August 19. In 2008, high OT pressure was associated with reduced nitrogen fertility, a phenomenon that has been demonstrated by Cornell entomologists again in 2009, 2010 and 2011 (Hsu et al.). In 2011, high OT pressure matched high available nitrogen on July 15-16 in the Safrane variety and when the varieties are pooled. In the Festival variety, the MT wheat had the highest available N and not the MT barley. On August 11-12, highest OT counts occurred where the N fertility and tissue N were lowest.
Perhaps the more important factor determining OT pressure in this trial was plant size. OT also colonizes larger plants first, which may partially explain why the larger plants in the MT system had higher levels of OT in July. OT move out of onion plants as they lodge. Since the onions in the conventional system matured later (Table 4) and thus had less lodging than the MT systems, this may explain why there was more OT in the plants in the conventional system than the MT systems in August. The reason why OT pressure was equally as high in the MT wheat as it was in the conventional despite similar lodging in the Festival variety may be because the plants were even larger (significantly more leaves and thicker necks than plants in MT barley) due to the significant stand reduction and thus, able to harbor more OT per plant.
% Lodging: Plants in the minimum tillage systems matured earlier than those in the conventional system. On August 11-12 when the plants were at the 8-9 leaf stage, the plants in the conventional system had 65 and 67% of the plants lodged in Festival and Safrane, respectively, compared to only 86 and 87% of the plants in the MT barley and MT wheat systems, respectively, in the Festival variety, and only 90% and 93% of the plants in the MT wheat and MT barley treatments, respectively, in the Safrane variety.
Delayed maturity of the conventional systems was likely a result of the unexplained stunting that occurred in this system; plants were simply not growing normally. In the 2008 study, the onions grown in the conventional system matured earlier than those grown in the MT systems with the onions in the MT wheat system being especially behind due to its having a significant stand reduction. High levels of N fertilizer can either delay maturity, or advance lodging. When stands are thin and grown under high nitrogen, as was the case in the MT wheat system, the plants develop thick necks and can support large top growth, and lodging is delayed. Alternatively, when plants are grown in normal or higher density and with high nitrogen, as was the case in the MT barley system in 2011, the plants have thinner necks that are less able to support large foliage and tend to bring adjacent plants down with them when they lodge, resulting in overall earlier maturity. Delayed maturity can be a detriment when the crop does not mature in time for a timely harvest.
Despite such a cold and wet spring, yields ranged from 351 to 509 cwt/A, which are considered average for direct seeded onions grown in New York on muck. Because of the tough spring, stands were highly variable throughout the field, so when collecting yield data, an attempt was made to pick sample areas with the best stands. Therefore, the yields from our trial are higher than the yield from the field at large. When the varieties were pooled across tillage systems, Safrane had significantly higher total marketable and jumbo sized bulb yield by 38 and 78 cwt/A, respectively, and significantly lower small and boiler sized bulb yield by 22 and 8 cwt/A, respectively. A significant variety by tillage type interaction occurred for total yield and all bulb size classes except jumbo. In Festival, the MT barley had significantly higher marketable yield than the conventional and MT wheat systems by 94 and 158 cwt/A, respectively. MT wheat had significantly lower total yield than the conventional by 64 cwt/A. In Safrane, MT barley and MT wheat both had significantly higher total marketable yield than the conventional by 82 and 77 cwt/A, respectively.
The majority of the marketable yield fell into the medium and jumbo bulb size classes. In Festival, MT wheat had significantly the highest jumbo sized bulb weight which accounted for 50% of the total yield, while the conventional system had significantly the lowest, accounting for 53% of the total yield. In the medium sized bulb class MT barley had significantly the highest weight, while MT wheat had significantly the lowest weight. MT wheat also had significantly the lowest weight of small and boiler sized bulbs. The conventional system had significantly the highest weight of boiler sized bulbs. In Safrane, both the MT wheat and barley had significantly higher jumbo weight than the conventional. No significant differences among treatments occurred in the medium sized bulb class. The two MT systems had significantly about twice as much jumbo sized bulb yield and significantly about half as much small and boiler sized bulb yield than the conventional.
Higher yields and larger bulbs in the MT systems may be a function of the higher available nitrogen throughout the season, but also because the onions in the conventional system were plagued by an unexplained stunting. During harvest, every attempt was made to pick sample areas of the best stand and quality of onions possible in each of the tillage systems to avoid confounding from the variability caused by the cool and wet spring. Unfortunately, the unexplained stunting in the conventional system was challenging to avoid. In the Festival variety, the high proportion of jumbo bulbs in the MT wheat system was due to the reduced stands; in onions, as plant population decreases, plant and bulb size increases.
No significant differences occurred among treatments for percent emergence, % dead seedlings, final stand or final yield. Emergence ranged from 70 to 81%. Total seedling death after 5 weeks ranged from 4.0 to 6.9%. It was not known definitively whether seedling death was caused by damping off pathogens, sunscald/heat stress or wind whipping; the dead or dying seedlings were all girdled at the soil line. At the end of the season at harvest on September 9, the final stand was about 45% of the original stand on May 25. At harvest, there was only 2.7 lb per 20 foot of row difference between the highest and the lowest yielding treatment. Numerically, the only consistent trend was that Pro Gro + Coronet + Allegiance + Ridomil had the highest emergence, third lowest seedling death up until the 2 leaf stage, highest final stand and second highest final yield.
The small-plot damping off trial was located in a section of MT wheat within the large trial. On June 15, stand represented 49 to 63% of the planted plant population in the trial. Comparatively, in the rest of the field, stand in the MT wheat system was 59% of the planted plant population in both varieties on June 3, and 47% in Festival on June 29, which were very similar to the stands in the small-plot trial. In the MT barley and conventional systems in the rest of the field, stand was 70% and 69%, respectively, in Safrane, and 89% and 83%, respectively, in Festival, on June 3. On June 29, stand was 74% for both MT systems in Festival. The fact that we saw no significant differences among nine different active ingredients belonging to five different chemical classes, most of which are known to have activity against damping off pathogens, Phythium spp., Fusarium spp. and Rhizoctonia spp., in combination with the fact that stand in the MT wheat system within the rest of the field was similar to the stand in our trial while stands in the conventional and MT barley systems were higher, strongly indicates that we can rule out damping off as the cause of the reduced stand in the MT wheat system. Further, since all commercially available fungicide seed and furrow treatments for onions were evaluated in this trial, we know that there are not any fungicides that growers can use to combat the soil microbes that may be causing reduced stand in a minimum tillage system where winter wheat is used as inter-row cover crop.
- Table 4. Stand, plant size and maturity
- Figure 6. Ground cover on May 10, 2011
- Figure 7. At harvest on September 13-14, 2011
- Table 8. Evaluation of fungicides for control of damping off pathogens
- Table 3. Ground cover and cover crop residue
- Figure 8. Ground cover and cover crop residue at 1 leaf stage on June 3, 2011
- Table 5. Nutrient availability
- Table 6. Pest pressure
- Table 7. Yield and bulb size distribution
The 2011 onion growing season was one of the worst on record in the Elba muck land, and the record-breaking cool and wet April and May certainly presented a lot of challenges for carrying out this project. Despite this, progress was made towards developing a minimum tillage system for direct seeded onions to prevent erosion of muck soils in large scale production with fall planted spring barley as an inter-row cover crop having the most potential.
Our first objective was to optimize ground cover to provide sufficient erosion protection without reducing onion yield, using inter-row cover crops, winter wheat and spring barley. By increasing the seeding rate of spring barley from 50 lb/A to 75 lb/A during the fall when establishing the cover crops, the amount of ground cover prior to planting in the spring increased from 10% to 30%. Remnants of this cover crop remained at harvest with 5% ground cover, which was at least 10 times more than the winter-killed oats in the 2008 study. The soil underneath the barley cover crop was about 0.3 to 1 inch higher than the surrounding bare-ground (Figure 10). Thus, this MT system was estimated to have kept at least 94,090 cubic inches or 2,249 lb per acre of muck soil from eroding from wind or water into the Oak Orchard watershed. Increasing the seeding rate of spring barley greater than 75 lb/A may increase ground cover and erosion protection even further.
In 2008, it was thought that having 60% of winter wheat ground cover just prior to planting was too much, because this amount of residue kept the soil cooler and wetter than the conventional and MT barley systems, which was thought to create a favorable environment for damping off pathogens that reduced onion stand by 50%. In 2011, ground cover of winter wheat just prior to planting was reduced slightly to 50%. Incorporating NPK fertilizer in the spring with cultivation quickly reduced ground cover to 26%, but by the end of the growing season, about the same amount of ground cover from cover crop residue remained (~30%). As in the MT barley system, the soil underneath the winter wheat cover crop was about 0.3 to 1 inch higher than the surrounding bare-ground (Figure 10). With 27% ground cover at harvest, the MT wheat system was estimated to have kept at least 508,084 cubic inches or 12,144 lb per acre of muck soil from eroding by wind or water into the Oak Orchard watershed. Even though ground cover of the barley nurse crop in the conventional system also had 27% ground cover at harvest, the soil underneath it was not raised (Figure 9). Despite this, it also provided protection against wind and water erosion, but not prior to its establishment. The advantage to a minimum tillage system is that the soil is protected from erosion from the time that the cover crop is established in the fall until harvest with the most critical 4-6 week period of protection being from early April until late May.
In this project alone, between the two minimum tillage systems on 20 acres, at least 6.0 million cubic inches or 143,928 lbs (= 72 tons) per acre of nonrenewable muck soil was prevented from being eroded by wind and water into the Oak Orchard watershed. Clearly, production of direct seeded onions in a minimum tillage system would preserve and prolong the useful life of muck soils while reducing environmental pollution from sediment and phosphorous loading into the waterways.
This study proved that winter wheat when used as an inter-row cover crop in a minimum tillage system in direct seeded onions in muck soil did not cause stand reduction due to increased damping off pathogens. Rather, the winter wheat either had allelopathic properties or otherwise somehow caused crop inhibition of the onions. Allelopathy is the inhibition of growth in one species of plants by chemicals produced by another species. Alternatively, the onion crop may have been weakened by a proliferation of soil microbes that were stimulated to grow because of the winter wheat cover crop, which in turn reduced onion stand. Whether the stand reduction of onions by the winter wheat cover crop was caused by allelopathy or another form of crop inhibition is unknown. If it was caused by soil microbes, unfortunately, our studies showed that there are no fungicides that onion growers can use to combat them, because none of nine different fungicides belonging to five chemical classes that were tested improved stand.
Because significant stand reduction (e.g. 50%) occurred in the MT wheat system in 2 out of 3 trials, it is too risky for onion growers to use winter wheat as an inter-row cover crop in the production of direct seeded onions in a minimum tillage system. Had we not followed through on testing our original damping off theory as the cause of this stand reduction, we would have just recommended that growers use additional fungicides for controlling damping off pathogens when they used winter wheat in a minimum tillage system. Consequent serious reductions in onion stand could cause onion growers to quickly become discouraged and this promising new technology could have been derailed before it even got started.
Our second objective was to optimize nutrient management including fertilizer application, understanding the dynamics of nutrient availability and to investigate the potential for reducing fertilizer rates in a minimum tillage system for onions. Applying NPK fertilizer in the spring and then incorporating it via multivator between the cover crop rows was a marked improvement over applying it in the fall and relying on in-season broadcast side-dress applications for nitrogen. When NPK was applied in the fall, an additional 56 lb/A of N was applied in the fall and 35-47% of the P applied in the fall was lost. Therefore, applying NPK in the spring saved $34.53 to $40.61 per acre in otherwise wasted N and P costs, and a total of $751.40 in the entire 20 acre field.
Our results suggested that the decomposing cover crops in the minimum tillage systems mineralized nitrogen that became available to the onion crop. We estimated this contribution to be about 20 to 25 lbs/A of N based on the amount of cover crop residue in the spring, but, it was not clear when exactly during the season it was released. We also suspected that depth of incorporation of NPK affected the availability of these nutrients with the shallower incorporation in the MT systems having increased availability. Clearly, further research is warranted to understand the dynamics of nutrient availability among these tillage systems where one has a spring killed cover crop and the other a winter killed cover crop, and the conventional system starts with no cover crop residue followed by a living barley nurse crop, which is then killed.
There appears to be potential to reduce fertilizer rates when onions are grown in a MT system. Starting in mid-July, soil and tissue nitrogen levels were quite high, especially in the minimum tillage systems, which was a good indication that the rates of nitrogen and possibly other nutrients can be reduced without having any effect on yield. Several recent Cornell studies have shown that rates of nitrogen fertilizer can be reduced to 75-90 lb/A without having any significant reductions in yield or bulb size (Hoepting, 2008; Hsu et. al. 2010; Hoepting et al. 2011).
In addition, recent Cornell studies including the 2008 minimum tillage study, have shown that high nitrogen rates of 125 lb/A and higher resulted in increased onion thrips pressure (Hsu et al. 2009, 2010; Hoepting 2008) and bacterial disease (Hoepting et al. 2010; Hoepting et al. 2011). As a result, several onion farms have experimented on their own with reduced rates of nitrogen (see section below on Farmer Adoption).
Despite very challenging growing conditions with the cool and wet spring, growing onions in the minimum tillage system with a spring barley inter-row cover crop resulted in an above average yield of 509 and 492 cwt/A for Festival and Safrane varieties, respectively and with 79% and 97% of the total weight falling into the higher priced medium and jumbo size bulb classes, the MT barley had the highest economic return. Unfortunately, yield could not be compared directly to the conventional system, due to the unexplained stunting confounding the true yield potential in this system. However, in our 2008 study, MT oats (763 cwt/A) yielded statistically the same as the conventional (707 cwt/A), despite having reduced nitrogen availability. Therefore, it is anticipated that onions grown in a minimum tillage system with a winter-killed inter-row spring barley cover crop will consistently yield the same as conventionally grown onions. In addition, the cost of establishing this minimum tillage system was just two-thirds the cost of establishing onions conventionally, and required 3 fewer passes across the field, resulting in less of a carbon footprint and reduced soil compaction (demonstrated in 2008 study).
Education & Outreach Activities and Participation Summary
It was planned to feature this project at Annual Elba Muck Onion Twilight grower meeting in early August 2011, but with the mediocre stands as a result of the wet spring, it was decided to not showcase this trials, if we wanted to encourage grower adoption.
With data entry and analysis behind due to a shortage in technical support for Hoepting, a presentation at the Empire Expo in 2012 was delayed. Plans are still in place to distribute project results via the Cornel Vegetable Program newsletter, Veg Edge and website and at future grower meetings as appropriate.
A presentation is scheduled for Hoepting to present, “Growing onions in a minimum tillage system”, which will include 2008 and 2011 studies, at the Great Lakes Fruit, Vegetable and Farm Markets Expo in Grand Rapids, Michigan on December 5, 2012. A proceeding will also be published for this presentation.
This research project was featured in the national 2011-2012 SARE Report from the Field in combination with my other NESARE onion projects in an article, “Research leads to profitable, sustainable approaches to onion production” by Sean McGovern. The article was later submitted as a press release on October 9, 2012, and subsequently re-written by Vicky Boyd, “New onion cultural practices help boost profits, protect soils”, which was published in The Grower (http://www.greenbook.net/news/New-onion-cultural-practices-help-boost-profits-protect-soil-173302421.html) and from there was dispersed to several websites and blogs.
The only areas where the cost of establishing the different tillage systems differed was with the cost of cover crop seed, killing the cover crops and the number of passes across the field to establish them (Table 9). Eighty to 86% of the cost of establishing a tillage system is the cost of fuel and labor for making trips across the field. The conventional system was the most expensive to establish which cost $168 per acre, because it required three extra passes in the spring including to disk, plant the barley nurse crop and then to kill the barley nurse crop in addition to the extra cost of the barley nurse crop. Establishing the conventional system cost 1.2x and 1.5x more than the MT wheat and barley systems, respectively. The MT barley system was the cheapest to establish, because it did not require a separate pass to kill it, because it was winter-killed.
Since the cost of establishing the tillage systems was minimal, the net return reflected the gross return, which was based on yield and bulb size (Table 10). The variety Safrane had the highest net return in each tillage system and the MT barley had the highest net return followed by MT wheat, which both netted more than the conventional. In Safrane, MT barley and MT wheat netted $2695 and $1997 more per acre than the conventional, respectively. In Festival, MT barley and MT wheat netted $1949 and $253 more than the conventional, respectively. Despite having only 50% stand, the MT wheat system in Festival still netted more than the conventional due to 50% of its marketable yield falling into the jumbo sized bulb class, which fetches a higher market price. If the mysterious stunting in the conventional system had not occurred, the yields would have been considerably higher and the MT wheat system in the Festival variety would not have done as well comparatively. In addition, the cost of onion seed is $400 to $500 per acre, which is a wasted input cost when only half of them produce healthy plants. In the 2008 study, yield, bulb size distribution and net return of the MT oats system was either equal to or greater than the conventional. Our 2011 study is the second to confirm that growing onions in an MT barley/oats system is economic feasible.
Our grower cooperator remains optimistic that onions can be grown in a minimum tillage system. His plan is to alternate this 30 acre field with minimum tillage direct seeded onions and onions grown from transplants. The early harvest of the transplanted crop will ensure enough time to get a cover crop established in the fall. Direct seeded main and late season onions are harvested later and proper establishment of a cover crop will not always be feasible. Demonstrated consistent success of growing onions in a minimum tillage system will encourage other growers to adopt this sustainable practice.
During our first attempt at growing onions in a minimum tillage system in 2008, we inadvertently demonstrated that onions grown with reduced nitrogen had significantly fewer onion thrips and comparable yields to conventionally grown onions. These preliminary results were used to acquire additional grants to investigate this relationship in depth. Since then several recent Cornell studies have shown that rates of nitrogen fertilizer can be reduced to 75-90 lb/A without having any significant reductions in yield or bulb size, while reducing onion thrips and bacterial disease pressure.
Consequently, several onion farms have experimented on their own with reduced rates of nitrogen:
• The grower cooperator for this project, reduced his rate of nitrogen from 125 to 75 lb/A in the year following the MT trial in the same field; he did not have to spray his onions with insecticides a single time for onion thrips, had <2% bacterial bulb decay at harvest and enjoyed a savings of $200 per acre in input costs. “I got my highest yields this year where I applied the least nitrogen” – Matt Mortellaro
• Triple G Farms of Elba reduced their rate of nitrogen from 120 to 90 lb/A, and saved two insecticide sprays for onion thrips, a savings of $130 per acre and a total of $21,450 on their farm in 2011.
• In 2011, onion grower, Joe DiSalvio, reduced his rate of nitrogen from 140 lbs per acre to 90 lbs per acre and achieved yields of 850 cwt per acre (almost double the state average) with <1 % bacterial bulb decay, representing a 66-fold reduction in bacterial bulb rot (down from 33% in 2010).
Areas needing additional study
Using winter killed spring barley as an inter-row cover crop proved to be the most effective means of successfully growing direct seeded onions in a minimum tillage system on muck soil. Further research is warranted to understand the dynamics of the availability of nitrogen as well as the other nutrients, especially phosphorous, in this minimum tillage system, as it appears that fertilizer rates could be reduced. Consistent results over different growing seasons are essential before recommendations should be made to growers.
Additionally, the dynamics of nutrient availability as it relates to the depth of tillage and fertilizer incorporation is warranted, because in this study, it appeared that shallow incorporation of fertilizer increased nutrient availability. Especially if reduced rates of fertilizer are feasible, investigating the application of banding fertilizer below the seed should be pursued. Differences in disease, insect or weed pressure should continue to be monitored so that any differences may be predicted and managed accordingly.
To further improve protection from erosion, it would be worthwhile to continue to strive for increased ground coverage and crop residue with winter killed spring barley as an inter-row cover crop. Increased seeding rates, earlier planting dates, and possibly different cereal cover crops should be explored. Finally, production of onions grown from transplants in a minimum tillage system is worthy of investigation.