Improving the profitability of onions grown on aging muck soil that has high pH
The challenge with growing onions on aging muck soils in the Northeastern United States is that the pH is above the optimum for growing onions, which results in reduced yield and profitability, and environmental contamination. If this pH issue could be addressed via altered management practices, the production of onions on aging muck soils could be sustained and phosphorous (P) loading into water ways reduced significantly. To remedy this situation, acid forming fertilizers including mono ammonium phosphate (MAP) and manganese sulfate were applied in a band at planting 2-3 inches below the seed, which should reduce the pH and improve the availability of P and manganese (Mn). Using this strategy, P is applied to the target area (i.e. within the reach of plant roots) where the pH becomes desirable for its availability (i.e. less than 6.0). Ultimately, the amount of P that escapes as a pollutant to waterways will be reduced, because it is not applied in the row middles where it is unavailable to the crop and free to escape into the environment. The focus of this project is to evaluate, demonstrate and encourage the adoption of this sustainable practice, as well as to evaluate whether foliar applications of Mn and P to onions deficient in Mn and P benefit the crop. Three on-farm small-plot field trials and a survey were conducted with five grower cooperators. The study was highlighted in a local newspaper article and at a twilight meeting which was attended by 34 growers and industry representatives. Data is being analyzed and results interpreted. We will use the results generated from this project to guide further research studies and to make fine-tuned recommendations to onion growers that will help them to become more profitable and better stewards of the land.
There is opportunity for growers to improve the productivity of onions grown on aging muck soils with high pH and to reduce phosphorous (P) loading into waterways by improving nutrient availability and uptake, especially of P and manganese (Mn). This may be achieved by applying these nutrients in an acidic fertilizer band 2-3 inches below the seed at planting and with nutrient foliar sprays. The focus of this project was to evaluate, demonstrate and encourage the adoption of these sustainable practices.
It is cost-prohibitive and impractical to reduce pH by applying sulfur to muck soils that contain extensive amounts of marl or free limestone (i.e calcium carbonate), as is the case in many of the muck lands in New York. However, it may be possible to reduce the pH within the plant row by applying acid forming fertilizers such as mono ammonium phosphate (MAP) and manganese sulfate applied in a band at planting 2-3 inches below the seed to improve the availability of P, Mn, zinc (Zn) and boron (B). Using this strategy, all of the P will be applied to the target area (i.e. within the reach of plant roots) where the pH will be desirable for its availability (i.e. less than 6.0). Ultimately, the amount of P that escapes as a pollutant to waterways will be drastically reduced, because it will not be applied in the row middles where it is unavailable to the crop and free to escape into the environment. Over time, it very well may be realized that with more efficient use of P, rates can be reduced for banding compared to broadcast applications. Fertilizer prices of P have at least doubled within the last 4 years, a trend that is not expected to retreat, thus in addition to the obvious benefits to the environment, using lower rates of P will reduce input costs considerably in the long term.
We conducted three small plot research trials in commercial muck onion fields with three grower cooperators in Orleans and Genesee Counties in New York, each with slightly different soil condition and fertility:
- Trial Site No. 1 (Batavia muck, CY Farms): high pH, low OM, low P, low Mn
Trial Site No. 2 (Webster muck, Star Growers): high pH, high OM, high P, low Mn
Trial Site No. 3 (Elba muck, Mortellaro): low pH, high OM, low P, high Mn
For the standard treatment, the full rates of nitrogen (N), P and potassium (K) according to a pre-plant Cornell soil test, were applied broadcast and incorporated prior to planting. For the banding treatment, up to 100 lb of P, the full rate of K and 4 lbs of Mn was applied 2-3 inches below the seed at planting. For this treatment, full rates of N (minus the amount applied in the band with the P fertilizer) and K was applied broadcast and incorporated. For these studies, N, P, K and Mn were in dry formulations of urea (46-0-0 NPK), mono-ammonium phosphate (MAP: 11-52-0 NPK), potash (0-0-62 NPK) and manganese sulfate 28%. The trials were set up as a randomized complete block (RCBD) design with 6 treatments (including those from objective No. 2) and 5 replications. Each treatment replicate consisted of the width of an onion bed (5 or 6 feet wide) with 4 to 6 onion rows per bed by 20 feet long. Broadcast fertilizer was spread by hand and raked in and banded fertilizer was applied with a push cone seeder set to a depth of 3 inches. Onions were seeded using the grower’s standard planting equipment, in-furrow fertilizer treatment and the onion variety that the rest of the field was planted to. Trials were established on April 21, 22 and 30 for Batavia, Elba and Webster, respectively.
To measure nutrient availability, soil samples were taken in mid-June at the 2-4 leaf stage and once plants started lodging in early- to mid-August, and sent to the Cornell Nutrient Analysis Laboratory (CNAL) for complete nutrient analysis. In addition, samples were collected from within and between the plant rows for each the banded and broadcast treatments in early June, late June and late July for analysis of pH. Leaf samples were collected for complete nutrient analysis of tissue at the end of July. Data has been entered, results need to be analyzed and interpreted.
To measure plant size, number of leaves and height of the tallest leaf per plant, were quantified three times throughout the growing season at the 2-4, 5-6 and 7-8 leaf stages in mid-June, late-June and mid-July, respectively. Trials were harvested on August 22, September 8 and 16 at Webster, Elba and Batavia, respectively. After windrowing, weight per grade was quantified. Data has been entered, results need to be analyzed and interpreted.
When pH is greater than 6.0, Mn, P, B and Zn can become tied up and unavailable to the plant. Since B deficiencies are rare and Zn levels tend to be high in New York, Mn and P deficiencies are most likely to occur on aging muck soils with high pH and were the focus of this project. Both Mn and P deficiencies result in slow growth, light colored foliage, delayed maturity and bulbing, and a high proportion of thick necks, all of which contribute to reduced yield and bulb quality. It is common practice for muck onion growers to apply Mn, and to some extent, P, as foliar sprays. These types of sprays are heavily marketed by fertilizer salesmen, but without any untreated controls, growers do not really know if they are getting a crop response. A crop response to these sprays would most likely occur on muck where the pH is high and P and Mn are low. Another question is whether foliar sprays of these nutrients alone without a fertilizer band, would be sufficient to correct a nutrient deficiency. If they are, than this would be a simpler technique for growers to adopt compared to banding fertilizer, because banding requires modifications to be made to their planters. If they do not result in a positive crop response, than growers do not need to continue investing in such sprays. In this project, we evaluated foliar sprays of P and Mn in the presence and absence of banding fertilizer on high pH muck soil to demonstrate if on their own they can induce a favorable crop response.
Treatments for this objective were included in the on-farm small-plot research trials for objective No. 1 in all three locations. Treatments included: 1) broadcast NPK + foliar Mn; 2) banded NPK + foliar Mn; 3) broadcast NPK + foliar P; and 4) banded NPK + foliar Mn + P. Foliar Mn was applied at 2 lbs per acre as manganese sulfate + manganese chloride 33% liquid in 30 gpa twice at the 2-3 and 5 leaf stages, using a CO2 backpack sprayer with 8002 nozzles and 45 psi. Similarly, foliar P was applied at 2 lbs per acre as Sol-U-Gro (12-48-8 NPK + micros) dry formulation in 30 gpa three times at the 2-3, 5 and 7 leaf stages. Data was collected for these treatments as described for objective No. 1.
The soil nutrient results from a survey in the Elba muck land in spring 2009 showed that lower levels of Mn tended to occur where the pH was above 6.0. However, low levels of P were not always associated with high pH. Out of the 39 sub-samples that had high to very high levels of available P, 26 (= 67%) of them had pH of 6.0 or higher. This may be related to individual grower practices. To better understand the relationship between pH, nutrient availability and yield under highly variable field conditions, we monitored pH and available macro-, secondary and micro-nutrients in the soil, and compared them to plant health and yield in several fields over a wide range of soil pH. The data that we generated from this study will allow us to fine-tune our recommendations derived from the fertilizer banding and foliar spray trials to different field situations.
For this study, 5 fields/blocks were selected, based on 2009 soil survey results where the pH varied from 0.6 to 1.4 units. In all the pH ranged from 4.6 to 7.1.
- Mortellaro, South Elba Muck land, Calarco Road, field No. 6, yellow onions
Panek, Central Elba Muck land, North of Sheelar Road, red onions
Star Growers, Webster Muck land, yellow onions
LS & Sons, Central Elba Muck land, field No. 6 south end for high pH and field No. 5 southeast end for low pH, yellow onions
LS & Sons, Central Elba Muck land, field No.4 north end for high pH and field No. 5 north end for low pH, yellow onions
In each field/block, three mini-plots each of high pH and low pH were selected, attempting to stay within the same variety. Each mini-plot consisted of 2 beds (10 or 12 feet) wide by 20 feet long. In mid- to late-July at the 7 to 9 leaf stage, composite soil samples were collected from each mini plot and sent to CNAL for complete nutrient analysis. At the same time, the inner leaves from 10 randomly selected plants were collected, washed and sent to CNAL for complete tissue nutrient analysis. Also, number of leaves and height of the tallest leaf per plant were quantified on 10 randomly selected plants per mini plot. At harvest, 100 randomly selected bulbs were collected per mini plot and yield by grade quantified. Data has been entered, results need to be analyzed and interpreted.
All three of our objectives were successfully met. We set up three on-farm small-plot research trials, each having different parameters with respect to pH, organic matter, and available P and Mn. We were challenged to find a soluble Mn foliar spray in the form of manganese sulfate and had to use a product that was a combination of manganese sulfate and manganese chloride. The trial at the Batavia site had very poor stands in the first two beds, which may have confounded our results. The cause of this was never determined. The trial in Webster muck had extremely high yellow nutsedge pressure and consequently the onions were very small. In setting up our first trial at the Batavia site, we had some challenges with the delivery of the fertilizer, particularly the finely ground manganese sulfate, and suspect that the actual rates delivered were lower than our target rates. We made adjustments to our seeder which improved the accuracy of the fertilizer delivery in the other two trials.
For our survey, we ended up having only 5 paired comparisons instead of 6, as originally planned. Unfortunately, in some of our comparisons we were unable to get the same variety for both the low and high pH mini plots. Also, in some of the paired comparisons, we did not get the degree of difference in pH between high and low mini plots as we had hoped. We did the best with could with the results that we had at hand from the 2009 spring soil survey.
The concept of this study was presented at the annual Elba muck onion twilight meeting on August 2, 2010 to 34 onion growers, industry representatives, and Cornell professionals.
Impacts and Contributions/Outcomes
This project was the first of its kind. Never before has such a comprehensive study been undertaken to improve the productivity of growing onions on aging muck soils with increased pH. Never before in New York has the practice of banding P been seriously considered. Before this project can have any real impact, our results need to be analyzed and interpreted and recommendations developed. Likely, more studies will need to be conducted to fine-tune our knowledge and understanding of this complex system. The next steps will be grower education, and on-farm demonstration and implementation. Without a doubt, there has been grower interest in banding P fertilizer and growers are eagerly awaiting the results of this study. It is our hope that this project will be the critical first step towards identifying, demonstrating and promoting relatively simple strategies that will improve the productivity and profitability of growing onions in the Northeastern United States, while reducing P loading into the waterways, thus sustaining large-scale commercial production of onions grown on muck soils and the quality of local water sheds for the long-term.
A newspaper article, “Researchers descend on muck for projects” published in the Batavia Daily News on August 31, 2010, featured this project among others that demonstrate the overall goal of sustainable onion production on muck soil. (http://thedailynewsonline.com/news/article_bed5d074-b468-11df-891a-001cc4c03286.html).
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