Nitrogen production of winter legumes as affected by phosphorus and lime

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Abstract
Winter legumes can benefit subsequent crops by improving soil and water conservation, and by providing N. The amount of N produced is influenced by soil pH, fertility level and other factors. Maximum N is essential for returns which will offset production costs. A two year study was conducted on a Norfolk fine sandy loam, (Typic Paleudult) to determine the effects of lime and P on nodulation and N production by winter annual legumes. Treatments consisted of 0, 123, and 246 Kg P/ha; 0 and 4.5 Mg lime/ha; and arrowleaf clover (Trifolium vesiculosum Savi), crimson clover (Trifolium incarnatum L.) and common vetch (Vicia sativa L.). The initial soil water pH was 5.1 and Mehlich No. 1 extractable P was 6 kg/ha. Dry matter yield responses to lime in 1981 occurred only with common vetch, and the differences between lime and no lime decreased as P rates increased. Without lime, soil pH levels dropped only slightly from 1981 to 1982, but they passed through the critical water pH of 5.0. The drop in pH increased exchangeable Al (Table 1) and resulted in large differences in yield between the lime and no lime treatments. The greatest yield increases with lime occurred with the early season’ harvest, and with arrowleaf clover and common vetch. As fertilizer P rates increased, differences between lime treatments decreased. With the highest P rate, dry matter yields with no lime were as high as yields with lime. Nitrogen production followed dry matter yield rather than % N patterns. Without P fertilizer, N production did not reach 100 kg/ha and production costs would have exceeded fertilizer N value. With 123 kg P/ha, all species were able to produce enough N to mitigate production costs.