Quantification of the impacts of organic and inorganic sources of nitrogen on nitrate leaching, water use efficiency, crop growth and carbon sequestration under rice-wheat cropping system

Pakistan is predominantly an arid country but it has one of the best and extensive irrigation systems in the world. Wheat (Triticum aestivum L.) and rice (Oryza sativa L.) are the major grain crops in the country. Soil health directly controls the growth and development of such crops. Integrated use of plant nutrients aims at combined use of inorganic and organic sources of plant nutrients with an objective to improve efficiency of applied nutrients, reduce environmental hazards and improve crop productivity. Organic materials markedly increase soil productivity by providing essential plant nutrients and by improving the physical properties of soil. The selected crops (rice and wheat) were grown in rotation up to maturity to study the effect of organic manures and mineral fertilizer on carbon sequestration and nitrate leaching. There were one pot study and two field studies. The Completely Randomized Design (CRD) with three replications was used in pot trials while Randomized Complete Block Design (RCBD) with three replications in field trials. The NPK and three organic sources (Farm manure, Poultry litter and Press mud) were applied as basal dose in all studies. Soil samples from 0-5, 5-15, 15-30, 30-60 and 60-100 cm depth were taken before sowing and after harvesting of each crop and analyzed for soil physicochemical properties. Agronomic parameters of rice (total biomass, plant height, grain yield, straw yield, number of tillers meter-2 , number of grains per panicles and 1000-grain weight) and wheat (total biomass, plant height, grain yield, straw yield, number of tillers m-2 and 1000grain weight) was recorded. The treatment 75N25PLT (75% N from chemical fertilizer+ 25% N from poultry litter) was best in case of yield and yield contributing parameters of rice and wheat. The maximum carbon sequestration rate was observed in treatment 100PMD (100 % RD of N through press mud) that was 1.77 Mg ha-1 year-1. It was observed that the hydraulic conductivity and infiltration rate had positive correlation with carbon sequestration rate. The soil hydraulic conductivity was 97 % correlated with carbon sequestration rate while infiltration rate was 95 % correlated with it. It was observed that the field saturated hydraulic conductivity and infiltration rate increased with increasing soil organic carbon. The data showed that the carbon sequestration rate was negatively correlated with soil strength with R2 0.92. So the soil strength decreased with increasing soil carbon