ABSTRACT
Sustainable nutrient management practices have the potential to enhance carbon (C) storage capacity of agricultural soils that may help offset increasing atmospheric CO2 concentration. Nutrient management practices on long-term basis differentially influence aggregates and distribution of soil organic C (SOC) present within aggregates, which in time may affect C stabilization. The present study assessed the impact of long-term application of fertilizers for 44 years either alone or integration with farmyard manure (FYM) on bulk density, SOC and C pools, potassium permanganate oxidizable C (KMnO4), aggregate stability and distribution of C fractions within different size aggregate under maize-wheat cropping sequence. The application of 100%NPK+FYM significantly (P< 0.05) improved soil aggregation and mean weight diameter (MWD). The percent of macro-aggregates (MacroA) and meso-aggregates (MesoA) was maximum in 100%NPK+FYM followed by NPK and the minimum in the control treatment. Irrespective of aggregate classes, TOC (g kg-1 aggregate) was maximum in 100%NPK+FYM treatment with an average of 8.42 g kg-1 aggregate as compared to control (5.05 g kg-1 aggregate). If averaged across the treatments, TOC concentration in aggregates followed the order MacroA> MesoA>MicroA. Correspondingly, results for KMnO4-C were similar in different treatments and aggregate classes. Application of FYM with inorganic fertilizers (NPK) or NPK showed a significant increase in all oxidizable organic C fractions particularly recalcitrant C fraction, which reflects the stable nature of OC as compared to very labile and labile C fractions. In general, C present in mineral fraction and large-sized aggregates (MacroA) has higher recalcitrant fractions of SOC as compared to small-sized aggregates (MesoF and MicroF). The study concluded that long-term balanced and integrated nutrient management improved soil aggregation, C distribution within aggregates, and C storage capacity of soils under maize-wheat. Carbon associated with macro aggregate and a mineral fraction has more recalcitrant C fraction compared to meso and micro aggregate fractions.
ABSTRACT
Aims: The present study investigated the effect of lowland rice soils of two regions viz. new alluvial and red-laterite on aggregate characterization and their associated organic carbon (SOC). Study Design: Randomized block design (RBD). Place and Duration of Study: New alluvial soils were collected from Jangipara block of Hooghly, West Bengal and Red-laterite soils were collected from Raghunathpur block of Purulia, West Bengal during 2017-18. Methodology: For each soil types (New alluvial and Red-laterite) five locations were identified and soil samples were collected from three depths i.e. 0-10, 10-20 and 20-30 cm. The aggregate characteristics i.e. water-stable aggregates (WSAs), mean weight diameter (MWD), aggregate stability and aggregate size fractions along with the distribution of carbon in those aggregate size fractions were critically studied. Results: The aggregate size as well as the stability decreased with increasing soil depth from 0 to 30 cm in both soils. New alluvial soils showed higher aggregate stability than red-laterite soils. Mean weight diameter (MWD) values of new alluvial soils were 34, 29 and 87% more than red-laterite soils at 0-10, 10-20 and 20-30 cm depth, respectively. Presence of higher amount of clay and organic matter in new alluvial made the difference in structural coefficient. The surface soil (0-10 cm) had more coarse aggregate (Cmac A >2000μ) fraction, however, microaggregates (<250μ) were dominant in lower depths in both soils. Water stable aggregates (WSA) in surface soils of new alluvial and red-laterite were 57 and 36%, respectively and were decreased with depth. Red-laterite produced higher micro aggregates as compared to new alluvial soils. Coarse macro aggregate fractions (>2000μ) retained maximum amount of soil organic carbon in both soils however, coarse micro aggregate associated carbon (Cmic AC<250μ) was captured in lower depths. New alluvial soils yielded aggregates with higher in diameter and stability coefficient that is due to higher amount of carbon stored in aggregates. Conclusion: The abundance of macro aggregate of New alluvial soils indicates better soil physical quality than Red-laterite soil which was dominated in higher micro aggregates leads to poor in structure and susceptible to water erosion.