Yields and nutrient relationships of corn grown in small grain-legume cover crops

Rising energy costs and high soil erosion losses are causing many farmers in West Tennessee to turn to no-tillage methods of production. This study, conducted during the growing season of 1980 at Milan, Tennessee, evaluated the effects of utilizing a legume in the no-till mulch on the growth, yield, and nutrient relationships of corn (Zea mays L.). Corn planted into a hairy vetch (Vicia villosa Roth.) and wheat (Triticum aestivum L.) mixture under both conventional and no-tillage was compared to no-tillage into a wheat alone mulch and to a check plot consisting of corn grown by conventional tillage into bare ground. These four treatments were compared at rates of 56, 112, and 168 kg/ha of nitrogen as NH₄NO₃. Tissue samples for dry matter weight and elemental analysis were taken of the wheat and wheat-vetch cover crops before corn planting and of the corn at five dates during the growing season. The corn was planted on April 30 and harvested September 12. The dry matter yield and N content of the wheat-vetch cover crop was lower than expected. This resulted in a very low N contribution from the mulch. Stover weight values were similar for all treatments across sampling dates at the non-zero N rates and the rate of dry matter production declined during the latter part of the growing season. These results reflect the severe moisture stress during this period. There appeared to be some immobilization of N under the no-till mulches. The WNT (wheat, no-tillage) treatment required the most supplemental N fertilization to reach its yield maximum. Also, the stover dry matter yield of both no-till treatments was lower than the conventional during the early part of the growing season. The analysis of variance for grain yields indicates that tillage was necessary to release the legume N and that there did not appear to be any priming effect from the addition of inorganic fertilizer N. These conclusions follow from the significant F value for the WVC vs. WVNT comparison and its insignificant interaction with N rates. Stover N content was significantly increased by additional fertilizer N. In some comparisons between treatments and between N rates, when dry matter and grain production were low there was a concomitant increase in the N content of the stover. There were significant decreases in the P and K percentages of the stover as the supplemental N rate was increased. These percentages also declined with increas-ing dry matter production. A concentration effect caused by low dry matter production at the low N rates during the first half of the growing season resulted in significantly higher stover P% values for the no-tillage treatments. A comparison of the data on stover yield and phosphorus uptake reveal that the wheat-vetch residue released available phosphorus at the 0 and 56 kg/ha N rates under both tillage situations.