부산대학교 도서관

Nitrogen (N) contributed by legumes is an important component of N supply to subsequent cereal crops, yet few Australian grain-growers routinely monitor soil mineral N before applying N fertiliser. Soil and crop N data from 16 dryland experiments conducted in eastern Australia from 1989-2016 were examined to explore the possibility of developing simple predictive relationships to assist farmer decision-making. In each experiment, legume crops were harvested for grain or brown-manured (BM, terminated before maturity with herbicide), and wheat, barley or canola were grown. Soil mineral N measured immediately before sowing wheat in the following year was significantly higher (P< 0.05) after 31 of the 33 legume pre-cropping treatments than adjacent non-legume controls. The average improvements in soil mineral N were greater for legume BM (60 [+ or -] 16kgN/ha; n = 5) than grain crops (35 [+ or -]20kgN/ha; n = 26), but soil N benefits were similar when expressed on the basis of summer fallow rainfall (0.15 [+ or -] 0.09 kg N/ha per mm), residual legume shoot dry matter (9 [+ or -] 5 kg N/ha per t/ha), or total legume residue N (28 [+ or -] 11%). Legume grain crops increased soil mineral N by 18 [+ or -] 9 kg N/ha per t/ha grain harvested. Apparent recovery of legume residue N by wheat averaged 30 [+ or -] 10% for 20 legume treatments in a subset of eight experiments. Apparent recovery of fertiliser N in the absence of legumes in two of these experiments was 64 [+ or -] 16% of the 51-75 kg fertiliser-N/ha supplied. The 25 year dataset provided new insights into the expected availability of soil mineral N after legumes and the relative value of legume N to a following wheat crop, which can guide farmer decisions regarding N fertiliser use. Additional keywords: canola, cereals, N uptake, pulses, rotation, sequence. Received 18 January 2017, accepted 20 June 2017, published online 13 July 2017
Introduction The concentrations of soil mineral (i.e. nitrate + ammonium) nitrogen (N) measured before sowing a cereal in dryland (rainfed) farming systems depends upon the relative balance between factors that [...]