Cover crop bicultures and their effects on phosphorus cycling and soil conservation
Cover crops have begun to receive a great deal of attention throughout the U.S. Corn Belt as a result of a recent focus on long-term soil quality. Oilseed radish (Raphanas sativas L.) (OSR) has become a popular cover crop among producers because of its many known benefits to soil. Characterized by a large tuber that penetrates the soil, OSR can take up large amounts of nutrients such as phosphorus (P) and can biologically till the soil before winter-killing in freezing temperatures. Because OSR has a low C:N ratio, it decomposes and releases nutrients rapidly in the spring. This rapid decomposition could leave released-P and bio-tilled soil susceptible to losses via runoff and erosion. Other species of cover crops such as oats (Avena sativa L.) and cereal rye (Secale cereal L.) have much higher C:N ratios than OSR, and decompose much more slowly in the spring. It is hypothesized that mixing OSR with oats or cereal rye as a biculture could still provide the desired benefits of an OSR cover crop while also maintaining released-P and bio-tilled soil with the presence of oats or cereal rye. In addition, it is well known that the presence of crop residues at the soil surface can have a significant impact on soil temperature and moisture. However, that effect can be different when the residue is in the form of living cover crops. Field studies were conducted at the Agronomy Center for Research and Education (ACRE) and Throckmorton Purdue Ag Center (TPAC) to observe the responses of soil P, runoff, and erosion to various cover crop treatments. The objective of this study was to observe the effects of four treatments: OSR (alone), OSR/Oats, OSR/Rye, and no cover crop on water soluble P and Mehlich-3 P levels over time, runoff and erosion, and subsequent crop performance. Plots were arranged in a randomized complete block design. Three fields were established in fall 2011, and one was established in fall 2012. The cover crop treatments tended to accumulate P over time at the soil surface and near the roots, but there was no difference in soil P among treatments by the V6 stage of the subsequent corn crop. Water soluble P and Mehlich-3 P levels following cover crops were similar to those before cover crops. The OSR/Rye treatment significantly decreased soil and P losses through runoff and erosion compared to the other treatments. An additional study was conducted at the Southeastern Purdue Agricultural Center to observe the effects of cereal rye cover crops on soil temperature and moisture. The objectives of this study were to observe the responses of soil temperature and moisture in plots with cereal rye or no cover crop at various times during the season. Cereal rye tended to result in cooler and wetter conditions in the spring, but did not have a significant effect during the growing season of the subsequent crop. Soil temperature and moisture following cover crops were not significantly different to the conditions prior to cover crops. It is hypothesized that this trend will begin to change after several consecutive years of cover crops.
Kladivko, Purdue University.
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