A Comparison of Cropping Systems Managed Conventionally or with Reduced Chemical Input

A Comparison of Cropping Systems Managed Conventionally or with Reduced Chemical Input

Summary

This project expands an ongoing experiment on reduced chemical input cropping systems. The long-term study was started in the Fall 1985 on a 6-hectare site in the Piedmont near Raleigh, NC. Continuous corn, continuous grain sorghum, corn-wheat-soybeans, and corn-wheat-soybean-corn-red clover cropping systems are managed conventionally (recommended rates of commercial fertilizer and pesticides) and with reduced chemical inputs (legumes for N, cultivation for weed control, no insecticide). The study is envisioned as an outdoor laboratory in which investigators from various disciplines monitor specific aspects of the experiment.

Project Results

The study was started in September 1985 on a Piedmont site near Raleigh. The core experiment consisted of four cropping systems: continuous corn, continuous grain sorghum, corn-wheat-soybean rotation (2-year), corn-wheat-soybean-corn-red clover rotation changed to corn-red clover-wheat-beans after the first cycle [4(3)-year]. Each cropping system was managed with CMP (no-till planting, recommended rates of fertilizer and pesticides) or RCI (conventional tillage, crimson clover or red clover as green manure crops, cultivation for weed control). Some of the core treatments were not very productive, so new RCI treatments were added to try to improve production: killing clover cover crops earlier to allow earlier corn planting, adding N fertilizer at planting, banding herbicides during cultivation, planting corn into mechanically killed or herbicide-kill strips in crimson clover, and adding N to wheat.

Crop Yields

Crimson and red clover cover crops varied in biomass production (1.7 to 3.5 tons/acre) and N accumulation (60 to 165 lb/acre) during the 7-year period.

In 1986-1988 and 1990 all corn yields were low (13-40 bu/acre) due to drought. In the other years, yields with CMP ranged from 60 to 130 bu/acre, and yields with RCI were up to 50% of CMP yields. Improved corn yield due to rotation was much more pronounced with CMP than with RCI.

Adding N to the RCI treatments at planting and banding herbicides at cultivation improved yields. For example, with continuous corn, RCI yields were comparable to CMP yields at the same N rate. Planting date had no consistent effect on yields. Yields of corn planted into killed strips of crimson clover (10 to 40 bu/acre) generally were not affected by kill method (mechanical or herbicide), but yields were lower than CMP yields. Low yields with RCI were due in part to competition from johnsongrass. Ear leaf N content was in the deficient range with RCI, suggesting insufficient N from the cover crops and/or competition from the johnsongrass.

Grain sorghum yields with CMP (15 to 40 bu/acre) were generally comparable to or greater than RCI yields. Effect of management on soybean yield (15 to 35 bu/acre) was mixed: 1986 and 1989, CMP=RCI; 1987 and 1992, CMP>RCI; and other years, CMP (3) Develop response functions based on various inputs (legumes, reduced fertilizer rates, cultivation, soil properties, etc.) and apply them to actual North Carolina farms to determine the effect of low-input methods on crop yields.

(4) Determine the economic impact of various reduced low-input methods on farm profitability.

(5) Develop extension programs to increase awareness of Extension agents and specialists regarding the scope and purposes of low-input agricultural systems; provide Extension agents and specialists with current and applicable research information on low-input agriculture from other studies