Author:
Armstrong R. D.,McCosker K.,Walsh K.,Millar G.,Kuskopf B.,Probert M. E.,Johnson S.,Standley J.
Abstract
Poor yields and low grain protein in cereal crops resulting from declining
soil fertility, especially nitrogen (N), are major threats to the grains
industry in central Queensland. The effect of 4 different pasture-ley legumes
[siratro (Macroptilium atropurpureum cv. Siratro),
lucerne (Medicago sativa cv. Trifecta), lablab
(Lablab purpureus cv. Highworth), and desmanthus
(Desmanthus virgatus cv. Marc)] on grain yield and
quality of sorghum crops was compared with that of a pulse (mungbean;
Vigna radiata cv. Satin) or continuous cropping with
grain sorghum (Sorghum bicolor).
Legume leys consistently resulted in large increases in grain yield
(188–272%), N uptake by sorghum (145–345%), and
grain protein (0.21–7.0% increase in grain protein) in sorghum
test-crops compared with continuous sorghum crops to which no fertiliser N had
been added. The positive effect of legumes persisted up to 3 sorghum
test-crops after only 1 year of legumes, although by the third year the effect
was comparatively small. Mungbean and lablab generally produced the largest
benefit in sorghum test-crops in the first year after legumes, whereas
desmanthus and lucerne produced the least benefit. Adding fertiliser N (up to
75 kg N/ha) significantly improved grain yields and N uptake of sorghum
test-crops in 3 of 4 years. However, responses to fertilisers were less than
those resulting from legumes, which was ascribed to increased availability of
legume N to sorghum.
Legumes progressively increased soil nitrate in all subsequent sorghum
test-crops (compared with continuous sorghum crops), rising from
6.8–18.9 kg NO3-N/ha after 1 year of legumes
to 24.2–59.6 kg NO3-N/ha after 3 years of
legumes. There was little difference between the legumes in their ability to
increase soil nitrate, with the exception of desmanthus, which consistently
resulted in the lowest amount of soil nitrate for subsequent test-crops and
lowest uptake of N by these crops.
Plant-available water content (PAWC) at planting of the sorghum test-crop was
only significantly (P<0.05) affected by previous
species in 1997, when it was lowest in plots previously sown to siratro and
lucerne and highest in sorghum and mungbean plots. In both 1996 and 1997,
plots sown to sorghum had significantly higher PAWC at anthesis and grain
maturity when previous plots were sorghum rather than legumes.
Subject
General Agricultural and Biological Sciences
Cited by
23 articles.
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