Influence of Cropping Sequence and Nutrient Management on Soil Organic Carbon and Nutrient Status of Typic Rhodustalfs

Influence of pigeonpea (Cajanus cajan L.) (Pigeonpea-rice-pigeonpea-rice), black-gram (Phaseolus mungo Roxb.) (Black gram-rice-finger-millet, (Eleusine coracana)-fallow) and rice (Oryza sativa L.) (Rice-rice-rice-rice) based cropping sequences with three levels of fertilizers viz. no fertilizer (control), recommended dose of NPK (RDF), and RDF + 2.5 t FYM on soil organic carbon (SOC) density and stock, available macro and micro- nutrients, soil pH, grain and straw yield was studied under split-split plot design from 2001 to 2004. Rice-based cropping sequence with RDF + FYM was more effective for enhancing SOC density (43.2%) and stock (40.6%) and in sequestering CO2 (30.32 t ha−1), while pigeonpea-based cropping sequence was more proficient in raising available nitrogen (45.8%), phosphorus (296%) and potassium (2.2%) as compared to others. Blackgram- and rice-based cropping sequences depleted available potassium by 13.0 to 18.6%, while pigeonpea-rice sequence in a cycle of four years enhanced the potassium availability by 9.9%. Latter also increased zinc availability (17.5 to 31.9%); reduced iron and manganese toxicity and maintained soil pHw, while rice-rice sequence during the period enhanced copper availability (254 to 316%). Blackgram- and rice-based cropping sequence increased soil acidity during the course of experimentation. Legume-based cropping sequence (pigeonpea and blackgram) with RDF + FYM treatments had greater affinity for nitrogen and phosphorus uptake, while rice-based cropping sequence absorbed significantly higher amount of potassium. The RDF and RDF + FYM application significantly enhanced the available nitrogen, phosphorus, and potassium over control and also raised SOC density by 27.6 to 43.2% over initial across the cropping sequences. Data revealed that pigeonpea-rice sequence with RDF + FYM was more beneficial for enhancing/maintaining soil fertility, while blackgram-rice and rice-rice sequence from 2001–04 produced higher grain yield at the cost of declining soil fertility.