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INTRODUCTION

Production of soft red winter wheat with conservation tillage in South Carolina has increased from about 5% of the planted acres in 1998 to over 20% in 2000. This increase in acreage has primarily been due to farmers wanting to increase the organic matter content of their soils and to the increased popularity of winged deep-tillage devices for conservation-tillage systems. The main benefits of conservation tillage for summer crops include increased soil water infiltration and lower soil temperatures. However, problems due to drought stress are usually less severe with winter crops than summer crops in this region, and soil temperatures during the fall and winter may be below optimum even with conventional tillage. Low soil temperatures can reduce wheat seedling emergence, early season growth, the final number of tillers (stems) produced per plant, and consequently, final grain yield.

OBJECTIVE

To identify the winter wheat production practices most suitable for conservation tillage systems.

APPROACH

In 1993, we began examining different management practices in an effort to optimize conservation tillage for winter wheat production on the southeastern Coastal Plain. Treatments that have been or are currently being evaluated include surface tillage, deep tillage, soil type, crop rotation, and nitrogen fertility. For most of these research studies, conservation tillage was compared to conventional tillage centered on disking the soil surface. No surface tillage was used for the conservation tillage treatment. When appropriate, the soil was deep tilled using a ParaTill.

RESULTS

In our initial studies, we found winter wheat grain yields to be similar for conservation and conventional tillage systems (Table 1). Deep tillage to disrupt soil hardpan layers was essential for both conservation and conventional tillage (Tables 1 and 2). Fewer wheat seedlings emerged with conservation tillage than with conventional tillage (Table 1). However, the plants grown with conservation tillage produced more tillers per plant to compensate for the fewer number of plants, resulting in the similar yields for the two tillage systems. In subsequent experiments, we consistently found fewer tillers and lower (usually about 10%) grain yields with conservation tillage (Table 2). With deep tillage, grain yields within each surface tillage treatment were similar for the different soil types tested. Grain yields were lower without deep tillage than with deep tillage for all soil types except for the relatively wet Rains sandy loam soil where yields were similar or higher without deep tillage. Crop rotation increased average grain yield by more than a third and reduced the yield loss associated with conservation tillage (Table 3).

In a recent study with conservation-tillage wheat, deep tillage reduced the number of plants that emerged but the timing (before versus after planting) and direction (parallel versus at an angle to the crop rows) of deep tillage had little effect (Table 4). Similar deep-tillage responses were found for grain yield (Table 5). Increasing the amount of fall N fertilizer resulted in fewer plants per yd2 (Table 4) but an increase in grain yield (Table 5). Wheat grown with the high fall N rate also had more tillers per plant and tillers per yd2 than the wheat grown with the low N rate (data not shown), which contributed to the higher grain yield of the wheat grown with the high fall N rate.

Disked, Deep Till

Tillage Direction

Tillage Direction

CONCLUSIONS

The benefits from conservation tillage on the southeastern Coastal Plain appear to be less for soft red winter wheat than for most summer crops. Wheat grain yields are usually about the same or less with conservation tillage than with conventional tillage, regardless of whether the soil is deep tilled or not. In most cases, lower yields with conservation tillage are associated with fewer emerged plants in the fall and fewer tillers (stems) per unit land area. Many Coastal Plain farmers are finding similar trends and switching back to disking the soil prior to wheat planting. Results from a recent study indicate that increasing the fall N fertility rate is one means to enhance the grain yield of wheat produced with conservation tillage and broadcast deep tillage. Our current research studies are focused on identifying additional production practices that will enhance wheat emergence and/or early season growth when conservation tillage systems are used.

For further information about this research, please contact: Dr. Jim Frederick 843-669-1912 ext. 228 email