Effect of soybean plant populations in a soybean and maize rotation

Effect of soybean plant populations in a soybean and maize rotation

2001

A:PS

Plant population of soyabeans (Glycine max) may influence the residual N contribution to a cropping system and yield benefits to the following cereals. Field studies were conducted from 1994 to 1996 on a N-depleted Sharpsburg silty clay loam soil at Mead, Nebraska, USA to: (i) determine soyabean yield at different plant populations; (ii) investigate residual N, chlorophyll-N-yield relations, and yield benefits from different soyabean populations following maize (Zea mays) crop; (iii) and compare N credits from soyabeans assessed with fallow and cereal plots as references. Eight soyabean populations from 14000 to 544000 plants/ha in narrow 50 cm rows, a fallow plot, and a maize plot were followed by maize in a rotation study. Soyabean yield was highest at populations of ?29000 plants/ha. Maize grain yields were highest following fallow and soyabean populations < 20000 plants/ha, intermediate following higher soyabean populations, and least in continuous maize. This is most likely due to N uptake as indicated by chlorophyll and N accumulation of maize. Nitrogen credits to maize were 16 to 46 kg N/ha when calculated as Nitrogen Fertilizer Replacement Values. This is probably overestimating the potential N contribution from soyabean because N credits from soyabean populations assessed with fallow instead of maize as references were negative. A net positive N balance due to soyabean reached a maximum of 17 kg N/ha, but soil N was depleted at populations < 20000 plants/ha. We conclude that yield increases of maize in rotation with soyabean may be due to N from reduced N immobilization, N added to the soil from N2 fixation, and possibly from non-N rotation effects such as water use efficiency.

v.93(2):396-403, AGRONOMY JOURNAL

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