Author
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Russelle, Michael |
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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 6/21/2014 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: The extent to which legumes add and retain N in agro-ecosystems depends on plant, rhizobial, soil, and weather conditions and on crop management. In some regions, deeply rooted alfalfa removes subsoil nitrate and water, reducing nitrogen (N) losses through leaching and tile drainage, fixes the remainder of its N requirements symbiotically, adds to the mineralizable soil N pool, which provides N to subsequent crops with lower nitrous oxide emissions than fertilizer, and yields a valuable high protein stored feed that improves milk and meat production, yielding manure that can be applied to fields that are deficient in N supply. Conversely, in humid region white clover-perennial ryegrass pastures, which are both shallow-rooted, nitrate leaching losses may be very high. Fixed N accumulates in soil during the legume phase through leaf drop, damage to herbage by livestock, harvest losses, root and nodule turnover, excretion of N from roots, and stand loss. These pools are relatively labile, so buildup depends on the balance between mineralization and addition. Fixed N can be transferred through this process to companion plants of subsequent crops. If the N requirements of the following crop are well synchronized with N mineralization from the terminated legume, very high N uptake efficiencies can be attained. Alternatively, significant N losses can occur if good synchrony is not achieved. Management of plant mixtures, stocking rate and timing, and the interval between the legume and the following crop are key determinants for retaining fixed N. |
