Management Strategies for Improved Soil Quality with Emphasis on Soil Compaction
Soil compaction is a common problem in many northeast vegetable farms because wet soil conditions frequently exist when farmers must enter the field with heavy equipment. Soil compaction can reduce yields of vegetable crops by 30% to 70%. Secondary effects of compaction, such as prolonged flooding and severe insect and weed pressure, contribute to yield losses, and can also result in increased use of pesticides for control of disease, insects and weeds. However, few farmers have evaluated crop-rotation options or the full arsenal of cover-crop species for their potential to prevent or remediate poor quality or compacted soils.
This project identified specific soil management practices that reduce root disease and soil-borne pathogen pressure. These include mechanical remediation procedures such as deep tillage or subsoiling and frost tillage, and bioremediation methods such as the use of cover crops, compost, and specific rotation sequences.
* Evaluate several winter cover crops, rotation crops, and cropping sequences for their effect on soil quality and soil compaction.
* Identify and integrate effective mechanical procedures for remediation of compaction with bioremediation approaches.
* Quantify the relationship between soil management practices and the occurrence of soil-borne pathogens and severity of root disease.
Sudan grass as a summer crop and perennial ryegrass as a fall or winter crop ranked highest among the 14 cover crops we evaluated with regard to remediation of soil compaction, ease of crop establishment, and year-to-year and site-to-site stability of performance.
Results suggest that including sweet corn and sudan grass in the rotation sequence may enhance or prolong the beneficial effects of a deep tillage operation on soil quality parameters, and may make the soil less susceptible to compaction.
Direct-seeded cabbage and snap beans were the crops most negatively affected by compaction, followed by cucumber, table beets, sweet corn and transplanted cabbage.
Activities and Results
Compaction is a common problem in vegetable production systems in the Northeast because farm operations sometimes require entering the field before the soil has adequately dried. Deep tillage to break up deeper compacted layers requires powerful tractors that are not available to some growers. Those who do try deep tillage find it is not a very effective solution, especially in the long term. Taking land out of vegetable production for two to three years in order to grow alfalfa, a known deep-rooted perennial, can be effective, but this is not an economically viable option for most vegetable farmers. Also, it can sometimes be difficult to establish a healthy alfalfa crop on compacted soils.
A three-year multi-site field study was conducted to evaluate various cover crops, rotation cycles, compost, and deep tillage for their impact on soil compaction, soil quality, the soil pests and diseases, and cash crop yield. Mechanical deep tillage (12 to 16 inch depths) on compacted sites had significant beneficial effects on soil quality parameters in the first year. Soil penetrometer resistance and bulk density were lower on deep-tilled compared to non deep-tilled plots. Porosity, water infiltration rate, time-to-ponding, and water holding capacity were significantly increased by deep tillage.
Effect on Crops
Direct-seeded cabbage and snap beans were the crops most negatively affected by compaction, followed by cucumber, table beets, sweet corn and transplanted cabbage. Yield response to compaction in the field is often associated with crop sensitivity to secondary effects of compaction, such as prolonged flooding after rainfall, reduced nutrient availability or uptake, and prolonged or more severe insect, disease, or weed pressure. Not surprisingly, deep tillage of compacted sites led to 10% to 70% increases in crop yields in the first summer after tillage.
Part of the benefit of deep tillage on snap bean yields was associated with less root disease. Of the five cash crops that we evaluated, sweet corn was best at producing roots that could penetrate into compacted soil layers. Sweet corn often produced substantial biomass on compacted soils, even when ear yields were reduced. These results suggest that sweet corn can be a good rotation crop to include on fields with shallow compacted layers, although it was not as beneficial as some non-cash cover crops evaluated.
Cover Crop Evaluation
Sudan grass as a summer crop and perennial ryegrass as a fall or winter crop ranked highest among the 14 cover crops we evaluated with regard to remediation of soil compaction, ease of crop establishment, and year-to-year and site-to-site stability of performance. Sudan grass had the deepest root system and generally ranked highest for root growth into compacted soil layers. Sudan grass also ranked high with regard to organic matter contribution, weed suppression, and suppression of parasitic nematodes and root disease of subsequent snap bean crops. Hubam sweet clover was another cover crop that consistently performed well, including growth on compacted soils. However, Hubam did not produce as much below-ground biomass as sudan grass or perennial ryegrass. Yellow blossom sweet clover, grown as a two-year crop, produces deep roots, but we did not have an opportunity to fully evaluate its performance on a compacted soil in our trials.
Grain rye, hairy vetch, and grain rye-plus-vetch mixtures are fall cover crops that frequently performed well, but they were not particularly effective at compaction remediation. Also, hairy vetch did not grow well on poorly drained, compacted soils, did not overwinter in some trials, and was associated with higher populations of parasitic root lesion nematodes in subsequent bean crops. Our results indicated that yellow mustard and other cover crops in the Brassica genus are potential soil compaction remediators because they produce deep, penetrating taproots. However, we encountered some problems in establishing a good stand in some sites in some years. More research is needed to determine optimum management practices under northeast conditions for all of these cover crops.
Soil Management and Rotation
Table beets responded very positively to addition of a composted chicken manure applied at rates between 2 and 5 tons per acre. Snap bean and sweet corn response to this compost was more variable, slightly increasing yields at one site, while having little effect or even a negative effect on sweet corn at the other site.
Our results indicated that bean monoculture without rotation to other cash or cover crops led to a decline in yield associated with an increase in root disease severity. Our data also suggested that rotation, particularly sequences that included sweet corn and sudan grass, enhanced and prolonged the beneficial effects of deep tillage on both the physical and biological properties of the soil.
Affect on the Soil Pest Complex
Root diseases caused by fungal and nematodal pathogens frequently reduce yields of many economically important vegetable crops of New York and the Northeast. Damage by root diseases is most severe on poor quality soils, such as compacted soils with poor structure and inadequate drainage, soils low in organic matter, and soils with low nutrient availability.
Increasing soil organic matter through the use of cover crops and green manures is well documented to improve soil physical and chemical properties, and also is known to increase the number and diversity of the total soil microbial community. The latter results in direct suppression of root pathogens and the production of bigger and more vigorous root systems that are tolerant to damage by root pathogens.
Our results have shown that the use of cover crops is generally beneficial in increasing yield and reducing root disease severity and crop damage. Bean monoculture without rotation to sweet corn or other cash or cover crops led to a decline in yield associated with an increase in root disease severity. Our results also documented that the various rotation cover crops are not equal in their impact in suppressing root diseases or the population of individual pathogens.
Frost Tillage as a Soil Management Option
Frost tillage is a primary tillage method that may be performed when a thin (1-to-4-inch) frozen layer exists at the soil surface. When frost enters initially unfrozen soil, the freezing-induced water redistribution causes soil drying below the frost layer and may therefore allow for tillage. A multiyear analysis of frost tillage demonstrated that this may be an attractive management alternative for vegetable growers in the Northeast, especially for early-season crops on medium- to fine-textured soils. Frost tillage allows spring field work to be performed during the winter and facilitates soil drying in the spring, thereby potentially reducing soil compaction from early field work. Using model simulations based on climate data from the Northeast, frost tillage opportunities occur most often (four to five days in the average per winter season) at the 40- to 43-degree latitude, with generally lower number of frost-tillable days to the north and south of this belt.
Direct-seeded cabbage was the most sensitive to soil compaction of all vegetable crops evaluated in our trials. A key factor in these yield reductions was more severe flea beetle pressure and damage during early growth stages in compacted plots. Cabbage seedlings grew much more slowly on compacted soil, prolonging the period when they are most subject to significant flea beetle damage. Weed competition was also more severe early in the season on compacted compared to non-compacted plots. Another factor causing yield reduction in compacted plots was stunted growth following periods of heavy rain because of poor drainage and a prolonged period of saturated soil conditions.
Transplanted cabbage was less sensitive to compaction than direct-seeded cabbage. Transplanted cabbage plants, because they essentially bypassed the early seedling stage in the field, were less affected by flea beetle damage and weed pressure early in the season compared to direct-seeded cabbage. Another factor may be that, in general, transplanted crops tend to have more prolific rooting of fibrous roots in the upper soil profile than direct-seeded crops. Location of the compacted zone, rainfall and irrigation patterns during the season, and ability of taproots to penetrate a compacted layer may determine whether the shallow rooting of transplants or deeper rooting of a direct-seeded crop is advantageous on compacted soil.
Snap beans ranked second to direct-seeded cabbage in yield sensitivity to soil compaction. One important factor involved in yield reductions on compacted plots was prolonged stunted growth after heavy rains due to poor drainage and extended periods of wet soil conditions, as was also observed for cabbage. Results of leaf tissue testing during the growing season revealed some nitrogen deficiency in compacted plots, which may also have been a yield-determining factor.
Results have generally shown that bean yields are increased and root rot is reduced after the incorporation of a green manure of grain crops such as oat, ryegrass, grain rye, barley, wheat, sudan grass, and others. Obtaining the benefit from cover crops in a bean rotation requires proper management of the cover crop. In particular, it is important to leave enough time, usually three to four weeks, between incorporation of the cover crop and seeding of the beans to allow for decomposition to occur.
As compared with beets, cabbage, snap beans and cucumber, sweet corn was less negatively affected by soil compaction in some sites in some years, although yields can still be reduced by 50% or more.
Reported April 1998. 1999 Northeast Region SARE/ACE Report.