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Decomposition
and nitrogen release by green manure legume residues in
different soil types
Jude J. O. Odhiambo
University of Venda, Department of Soil Science, Private Bag
X5050, Thohoyandou, 0950, South Africa. E-mail:
Jude.Odhiambo@univen.ac.za
.Tel: +27 15 962 8431. Fax: +27 15 962 4749/8598.
Accepted 19 November, 2009 |
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A laboratory incubation experiment was conducted over a
16-week period to determine decomposition and N release by
three green manure legume species, Mucuna (Mucuna
pruriens), Lablab (Lablab purpureus cv. Rongai)
and Sunhemp (Crotalaria juncea), in three soil types
from South Africa. The amount of N mineralized from the
residues was determined at 2, 4, 8 and 16 weeks from the
onset of incubation. Nitrogen release pattern of the three
legume residues followed a similar pattern in all the three
soils, with sunhemp treated soil having the highest amount
of mineral N after 16 weeks of incubation in all the three
soils, followed by lablab and then mucuna. The amount of
mineral N ranged from 121 to170, 96 to 134 and 92 to 108 mg
kg-1 in the sunhemp, lablab and mucuna treated
soils, respectively. The cumulative amounts of N from the
legume residues mineralized recovered as mineral N in soil
after 16 weeks of incubation ranged from 21 - 41% (92 - 121
mg kg-1), 30 - 68% (108 - 170 mg kg-1)
and 26 - 60% (93 - 147 mg kg-1) of the initial
added N contained in the residues in the soils with 62, 20
and 12% clay contents, respectively. Less than 50% of the
initial added N was mineralized in the high clay content
soil. Mineralization rate constant, k, was
significantly correlated to the residue N content, net
mineralized N, C/N ratio and Lignin/N ratio. Results from
this study indicated that all the three legumes could
contribute significant amounts of N for uptake by plants,
with sunhemp tending to release N at a faster rate, followed
by lablab and then mucuna. High clay content in soil slowed
down N mineralization.
Key words:
Green manure legumes, incubation, decomposition, N release,
soil type. |
