Influence of Crops and Different Production Systems on Soil Carbon Fractions and Carbon Sequestration in Rainfed Areas of Semiarid Tropics in India

Organic agriculture’s economic benefits and widespread adoption are well documented, but its impact on soil C dynamics in rainfed regions of semiarid tropics is less understood. The use of organic amendments in organic farming not only supply nutrients but also have the potential to contribute to soil carbon sequestration. Carbon storage and various soil organic pools are affected differently by various crops and production systems. A study was conducted with three crops (sunflower, pigeonpea, and greengram) under three production systems (control, organic and integrated) to assess the effect on soil C stocks, carbon sequestration potential, and crop yield. After seven years of experiment, pigeonpea (Cajanus cajan L.) cultivation improved soil bulk density, porosity and water holding capacity compared to greengram [Vigna radiata (L) Wilczek] and sunflower (Helianthus annuus L.). Furthermore, plots under pigeonpea cultivation being on par with greengram had 15.6% higher total C (113.52 Mg C ha−1), 14% higher easily oxidizable organic C (17.5 Mg C ha−1) and C sequestration rate of 1.22 Mg C ha−1 yr−1 compared to sunflower. Among the three production systems, plots under organic management had significantly lower bulk density and higher water holding capacity and porosity at all of the profile depths compared to integrated production system and control. Similarly, organic production system being on par with integrated production system improved the easily oxidizable, oxidizable and weakly oxidizable organic C fractions at different soil depths compared to control. The C sequestration rate ranged from 0.21 to 0.85 Mg C ha−1 yr−1 in organic production systems compared to negligible rate (0.01–0.04 Mg ha−1 yr−1) in the plots under control. On average, integrated production system being on par with organic management recorded significantly higher pigeonpea equivalent seed yield (886 kg ha−1) compared to control (792 kg ha−1). These results suggest the potential of organic production system in improving soil properties, C sequestration, and crop yields in semiarid rainfed areas