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Influence of a legume green manure crop on barley straw/stubble decomposition, and soil nitrogen retention and availability
Influence of a legume green manure crop on barley straw/stubble decomposition, and soil nitrogen retention and availability
Kapal, Debbie B.
Kapal, Debbie B.
Date
2008
Type
Thesis
Fields of Research
Abstract
The incorporation of cereal straw/stubble often immobilises nitrogen (N). This can help
conserve N in soil in organic forms, thus reducing loss through leaching over dormant
winter periods. However, N-depressions that arise during decomposition can reduce crop
yield. The inclusion of a legume green manure can supply fixed-N, thus alleviating the low
N availability to crops. In this study, the effect of lupin (Lupinus angustifolius L.) green
manure incorporation on barley (Hordeum vulgare L.) straw/stubble decomposition, and N
availability was investigated. A field experiment was used to determine the effects of the
green manure on decomposition. Decomposition of straw/stubble was monitored using the
litterbag technique. Following green manure incorporation, soil cores were incubated in a
glasshouse to determine mineral-N availability. Though not significant, the inclusion of
lupin green manure seemed to increase the decomposition of straw/stubble during the
growth period, then slowing it after its incorporation at 110 d. This was described by a
logarithmic pattern of loss of - 4.97 g AFDW residue day⁻¹, with 60% remaining after 140
d. Treatments without lupin had a linear decomposition of - 0.12 g AFDW residue day⁻¹, with 49% remaining after 140 d. The loss of cellulose confirmed the differences in
decomposition with the inclusion of lupin resulting in 2.79% less cellulose remaining in
straw/stubble after 140 d compared to its exclusion. Lupin significantly increased pot oat N
uptake and DM yield by 55 % and 46 %, respectively, compared to its exclusion. However,
this effect was not observed in field sown wheat yields and the soil mineral-N
measurements made. This study showed that the potential of lupin to increase
straw/stubble decomposition by improving the retention and availability of N, leading to
long-term yield benefits, needed further investigation.