Reducing soil erosion and nitrogen leaching through sustainable cropping systems

View the project final report

• 2006 annual report

Commodities

• Agronomic: barley, oats, rye

Practices

• Crop Production: cover crops, no-till
• Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research, participatory research
• Soil Management: soil analysis, soil quality/health

A Virginia study evaluating cover crop species at three plating dates with or without winter nitrogen application determined that rye and rye + hairy vetch yielded significantly more biomass than other species. Rye nitrogen uptake was also greater than other cereals. Early planted rye reduced total soil profile NO3- (0-90 cm) by 15 kg ha-1. Across species, early planting resulted in 21 kg ha-1 less soil profile NO3- in May than late planting. Averaged over cereal cover crops, N applied at GS 25 resulted in 2.1 Mg ha-1 more biomass and 26 kg ha-1 more N uptake.


Tables, figures or graphs mentioned in this report are on file in the Southern SARE office.
Contact Sue Blum at 770-229-3350 or
sueblum@southernsare.org for a hard copy.

Introduction

Improved water quality in the Chesapeake Bay has been a long-term concern in Virginia and other Mid-Atlantic states. Today, the importance of water quality, and the role of agriculture in maintaining water quality, is apparent throughout the United States. The Chesapeake 2000 agreement, a strategic plan to maintain abundant, diverse populations of living resources, fed by healthy streams and rivers, sustain strong local and regional economies, and maintain quality of life in the region was adopted in June 2000 (Chesapeake Bay Program, 2000). Chesapeake 2000 calls for the development of locally supported watershed management plans in two-thirds of the Bay watershed, continued efforts to achieve and maintain the 40 percent nutrient reduction goal agreed to in 1987, and correction of the nutrient- and sediment-related problems in the Chesapeake Bay and its tidal tributaries sufficiently to remove the Bay and the tidal portions of its tributaries from the list of impaired waters under the Clean Water Act by 2010. These goals make it imperative that growers utilize land and nutrient resources efficiently. Winter annual cover crops are an important tool for water quality protection because they can scavenge and utilize soil nutrients, especially nitrogen (N), which could otherwise be lost from the soil/plant system through leaching and runoff during winter months.
Beneficial effects of cover crops and crop rotation have been recognized for many years. As early as 3000 years ago, growers were using green manure cover crops to improve soil fertility. However, the steady increase of inorganic fertilizer use over the past 60 years and the development of more modernized farming techniques have resulted in less diversified cropping systems. Increasing environmental concerns associated with fertilizer lost from the agricultural system, soil erosion, and high production costs coupled with low commodity prices have led many growers to reexamine cover cropping as a method of increasing soil productivity. Noted effects on soil characteristics as a result of cover crops include increased organic matter, greater water- and nutrient-holding capacity, N contribution from legumes, improved tilth and aggregate stability, and reduced erosion.
Soil organic matter (SOM) content directly influences many biological, chemical, and physical properties that affect productivity. The greatest contributor to SOM is crop residue. One of the many benefits of higher organic matter content in soils is improved water-holding capacity. Soil organic matter can hold up to 20 times its weight in water (Stevenson, 1982). This can significantly increase the amount of plant-available water, particularly in sandy soils. Even in high-rainfall regions, moisture is often a limiting factor in crop production, therefore, greater plant-available water, due to higher SOM content, can increase yield by improving the overall water use efficiency (crop yield per unit of water; WUE) of the crop.
The crumbly, friable, well-aerated soil structure associated with good tilth is desirable due to improved drainage, reduced crusting and ponding, and ease of seedbed preparation for following crops. Crop rotation improves soil structure by reducing the impact of compaction by increasing aggregate stability, the measure of the resistance of soil aggregates to being broken down when subjected to disruptive forces, such as heavy machinery traffic. As early as 1967, researchers noted that aggregate stability increased from 67 to 76% when alfalfa was added to a corn-barley-sugarbeet rotation (Schumaker et al., 1967). More recently, similar results have been published documenting that aggregate stability is consistently higher under legume (alfalfa or red clover)-corn rotations compared with continuous corn (Raimbault and Vyn, 1991). Increased aggregate stability also reduces erosion by making the soil less vulnerable to the destructive forces of wind and rain.
Research cited by Peel (1998) found greater than 50% reduction in soil erosion when corn, barley, and hay were rotated compared with soil erosion from land in continuous corn. The decrease in soil loss when crop rotation and cover crops are employed is due to several factors. These factors include the dense canopy of the forage, reduced cultivation when the soil was in forage, the more extensive root system of the forage, and the increased amount of residue returned to the soil as a result of crop rotation. Reduced soil loss not only benefits crop production, but also decreases the potential for surface runoff of sediment containing nutrients and pesticide residues.

Determine the winter cover crop species and planting date that provides the most vigorous winter soil cover, the greatest biomass return to the soil system, and the highest level of N uptake.
Determine the change in soil nitrate (NO3-) over the cover crop season.
Evaluate cover crop effects on subsequent crop weed control.
Educate producers and agricultural professionals on how to successfully implement cover crops to maximum environmental and economic advantage.