Effects of 42-year long-term fertilizer management on soil phosphorus availability, fractionation,adsorption–desorption isotherm and plant uptake in flooded tropical rice

Soil phosphorus(P) fractionation, adsorption, and desorption isotherm, and rice yield and P uptake were investigated in flooded tropical rice(Oryza sativa L.) following 42-year fertilizer and manure application. The treatments included low-input [unfertilized control without N, P, or K(C0N0)], farmyard manure(FYM)(C1N0), NP(C0NP), NPK(C0NPK), FYM + NP(C1NP), and high-input treatment, FYM + NPK(C1NPK). Grain yield was increased significantly by 74%over the control under the combined application of FYM + NPK. However, under low- and high-input treatments, yield as well as P uptake was maintained at constant levels for 35 years.During the same period, high yield levels and P uptake were maintained under the C0 NP, C0 NPK,and C1 NPK treatments. These are unique characteristics of a tropical flooded ecosystem, which is a self-sustaining system for rice production. The Fe–P fraction was highest compared to the Ca–P and Al–P fractions after 42 years of fertilizer application and was significantly higher under FYM + NPK treatment. The P adsorption capacity of soil was highest under the low-input treatment and lowest under long-term balanced fertilization(FYM + NPK). In contrast, P desorption capacity was highest under NPK and lowest in the control treatment. Long-term balanced fertilization in the form of FYM + NPK for 42 years lowered the bonding energy and adsorption capacity for P in soil but increased its desorption potential, increasing P availability to the plant and leading to higher P uptake and yield maintenance.

Life cycle greenhouse gas emissions from five contrasting rice production systems in the tropics

Carbon footprint (CF) quantification of major rice production systems (RPSs) is a prerequisite for developing strategies for climate change mitigation in agriculture. Total life cycle greenhouse gas emissions (LC-GHGs) from rice production to consumption might provide precise CFs for RPSs. Therefore, we assessed three segments (pre-farm, on-farm, and post-farm) of LC-GHGs under five major contrasting RPSs, i.e., aerobic rice (AR), shallow lowland rice(SLR), system of rice intensification (SRI), deep water rice (DWR), and zero-tilled direct-seeded rice (ZTR), in India to determine the corresponding CFs.Carbon footprint was the lowest for ZTR, while LC-GHGs were the lowest for AR. Therefore, AR is an adequate option for short-term reduction of GHG emissions. However, ZTR might be promoted by incentives as a long-term strategy. Among segmental LC-GHGs, on-farm GHG emissions contributed less than the other two segmental GHG emissions. The post-farm (i.e., farm gate to consumption) segment contributed the largest proportion (54%–69%) of total LC-GHGs, followed by pre-farm (i.e., cradle to farm) segment (21%–27%) and on-farm operation (11%–23%). These findings suggest that post-farm components that contribute to maximum GHG emissions must be scientifically tackled with proactive policy initiatives. However, the data of this segment are limited and scattered. Therefore, real-time assessment of GHG emissions during post-farm operation and input transportation from cradle to farm requires more precise quantification. Although CF in SRI was higher, this system had the potential to achieve higher yields and better soil carbon storage. Therefore,SRI may be encouraged from the perspectives of food security and long-term sustainability by reducing GHG emissions by three to four times.