Cropping system and antecedent carbon level effects on soil organic matter and nitrogen dynamics
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Date
2019
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Punjab Agricultural University, Ludhiana
Abstract
Land-use and agricultural management are known to impact organic matter and nitrogen (N)
dynamics in soil. Besides climatic conditions, the effect of land-use and management depends on
choice of the cropping sequence that governs the magnitude and composition of plant-derived
carbon (C) input to soil, and the soil organic C status which is central to most of the physical,
chemical and biological processes. Although the effect of cropping systems on soil organic carbon
(SOC) and N dynamics is fairly documented, yet the information on their influence on soil C and N
dynamics vis-à-vis antecedent C level is scanty. In the present study, impact of maize-wheat and
soybean-wheat cropping in reference to continuous fallow, on total and labile pools of SOC and N
dynamics in four soils of different antecedent C level was investigated. In soils of low to
intermediate C level, cropped soils lost 11.7 to 21.6% C compared to continuous fallow, however, in
a high C soil the cropped soils could maintain soil C status similar to fallow soil. However,
compared to antecedent C stocks, the average soil C stocks in the plough layer (0-15 cm) under the
three land-uses were improved (0.55 to 1.41 Mg ha-1) in soil of low antecedent C level, but depleted
(0.04 to 3.64 Mg ha-1) in soil of high antecedent C level. Compared to fallow soils, the cropped soils
had lower concentrations of water soluble (17.7 to 40.5%), hot water soluble (18.1 to 25%) and
KMnO4-oxidizable (16.5 to 29.2%) carbon. In soils of intermediate to high antecedent C level,
cropped soils being lower (7.9 to 12.4%) in very labile pool and higher in recalcitrant pool (6.4 to
29.4%), had greater stabilization of soil C than continuous fallow. While both the cropping systems
exhibited lower C mineralization (31 to 54%) than fallow in low to intermediated C levels, the two
cropping systems revealed contrasting N mineralization kinetics in soils with intermediate to high C
levels; maize-wheat exhibited higher (8.5 to 9.8%), but soybean-wheat showed lower (upto 8.1%) N
mineralization compared to fallow. Maize-wheat influenced nitrification potential only in low C soil
(19% higher than fallow) whereas soybean-wheat in intermediate C soil expressed opposite results
to that in high C soil. Compared to fallow, soybean-wheat exhibited lower (8-14%) nitrification
potential in medium C soil, but higher (17%) potential in high C soil. In conclusion, choice of a
cropping sequence in a soil must consider the antecedent soil C status in predicting the magnitude
and direction of changes in soil C and N pools.
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