Availability of N to plants from legume and fertilizer sources: which is greater?
van Kessel, C.
One benefit often cited for legumes crops is that they contribute N to subsequent crops, but the magnitude of this effect has been difficult to quantify. A study was conducted to compare how much and when N from fertilizer and residue sources was taken up by wheat Wheat straw (W), lentil straw (L), and lentil green manure (G), unenriched or enriched in 15N, were both surface placed and incorporated into microplots (10 x 40 cm) in the field in the fall of 1988. In the spring of 1989 wheat was planted in all microplots, and unenriched and enriched fertilizer N was added to microplots containing enriched and unenriched plant residues, respectively. Microplots were destructively sampled at planting and at 6, 10 and 13 weeks after planting. Approximately 29 % of added fertilizer was recovered in wheat tops by 6 weeks after planting in all treatments except incorporated W, where immobilization reduced this value to 19 %. Maximum recoveries of fertilizer 15N were 34 % by the final sampling date. The proportion of residue 15N recovered in wheat tops at the final sampling dates was 19 and 11 % from incorporated and surface-placed G, respectively, and 5.4 and 5.3 % from L and W, respectively. Surface placement of residues reduced immobilization of fertilizer N but increased losses of residue N. Comparisons of N availability based on recovery of 15N may be misleading because 15N recovery does not account for changes in mineralization of native N, which is likely to be affected unequally by the addition of different N sources.
Soils and Crops Workshop