Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 23, 2010
Publication Date: June 29, 2010
Citation: Russelle, M.P. 2010. Compatibility with corn: N credits [abstract]. Proceedings of the Alfalfa/Corn Rotations for Sustainable Cellulosic Biofuels Production, June 29-30, 2010, Johnston, Iowa. Available: http://www.alfalfa.org/2010WS/Russelle.pdf. Technical Abstract: Productive and efficient short rotations of alfalfa and corn are needed to reduce energy inputs, produce food, feed, and energy, and yield the environmental quality benefits from the perennial legume. After decades of research, however, farmers and their advisors still question how much fertility alfalfa confers to the following crops. Increased N supply involves both short-term (the first few following crops) and long-term effects. From the perspective of first-year corn, there is a high probability of yield response to additional N when grown after alfalfa stands that are less than 1 year old. The increased N availability in these fields usually is not sufficient to support maximum corn yield, although incorporating more alfalfa regrowth reduces the amount of additional N needed by the next corn crop. In contrast, corn response to additional N is unlikely after one or more production years of alfalfa. In 95% of about 140 site-years, corn grown after alfalfa required no additional fertilizer N beyond a starter application (about 30 kg N/ha). Alfalfa stand densities, timing of stand termination, tillage, inherent soil N supply, soil texture, and the amount of incorporated alfalfa herbage are used to help predict which fields may show a response to N, but the reliability of many of these factors is low. As a result, there is little consistency in state-to-state N credit estimates. Similar to N credits with manure, alfalfa N credits decline for the second year of corn, are much more variable, and range from 0 to 90 kg N/ha. Nitrate leaching losses after first-year corn may contribute to loss of N in these rotations. Benefits of alfalfa to longer term soil N supply have been rarely quantified and therefore are not predictable. High priority research objectives related to N cycling in these rotations include: 1) assess net N contributions to the soil and following crops by diverse alfalfa germplasm grown for one or two production years; 2) develop corn hybrids with soil N uptake and assimilation that extends into the autumn; 3) optimize low cost cover cropping approaches to capture and recycle residual alfalfa N; 4) devise more reliable predictive equations for the second-year alfalfa N credit; 5) develop alfalfa germplasm and management systems that enhance late fall herbage regrowth; 6) develop alfalfa germplasm with young (2- to 3-yr-old) root systems with high N content that also resist decomposition; and 7) quantify trends in soil organic N over time in model crop rotation and management systems in order to determine characteristics that can maintain long-term soil fertility.