Effect of organic and inorganic sources of nutrition on nitrogen and potassium dynamics in soil

Nitrogen and potassium dynamics in soils is largely affected by the changes in organic matter content of soil. Use of high analysis fertilizers only, has lead to the depletion of organic matter content of soils and the deficiency of nitrogen has become widespread. Similarly, increase in soil K depletion has also been observed in India. The present study entitled “Effect of organic and inorganic sources of nutrition on nitrogen and potassium dynamics in soil” comprised of laboratory incubation study and field experiment. Field experiment is in progress on a sandy loam soil at Punjab Agricultural University Farm on basmati-wheat cropping sequence since rabi 2006-07 to study the effect of fertilizer management practices on crop yield and soil properties. The fertilizer treatments consisted of inorganic fertilizers, organic manures and integrated nutrient management (INM). Soil samples were collected from 0-15 and 15-30 cm soil layers from different treatments after five cycles of cropping. The results showed that soil organic carbon (SOC), mineral nitrogen and total nitrogen content in surface soil (0-15 cm) ranged from 0.33 to 0.56 g 100 g -1 , 29.2 to 65.3 and 200 to 967 mg kg -1 , respectively. Soil organic carbon, mineral and total N content decreased in the sub-surface layer (15-30 cm) in all treatments. Water soluble, exchangeable, available, non-exchangeable, lattice and total K content in surface soil ranged from 35.0 to 104.2, 58.3 to 150.8, 23.3 to 48.3, 580 to 948, 10453 to 14245 and 11033 to 15087 mg kg -1 , respectively. Water soluble and available K content of the surface soil was higher than subsurface layer. However, non-exchangeable, lattice and total K content were higher in sub-surface soil layer in all treatment plots. Different forms of K, except non-exchangeable, were significantly higher in 400 kg N ha -1 from RSC treatment whereas non-exchangeable K was significantly higher in plots receiving 400 kg N ha -1 from FYM. Soil organic carbon, mineral and total nitrogen and different forms of potassium were higher in plots receiving organic manures (farm yard manure, FYM, vermicompost, VC and rice straw compost, RSC), than integrated nutrient INM and recommended fertilizer (RF) treatment. A significant decrease in soil pH and EC was observed in organic treatments plots over the other treatments at both the soil depths. Wheat grain yield, straw yield and nutrient uptake were significantly higher in INM2 (recommended fertilizer plus 200 kg N ha -1 from FYM) treatment than all other treatments. Ammonical, nitrate, mineral and cumulative nitrogen mineralized were higher in soils receiving organic manures than INM, RF and control treatment soils at all the temperatures (15, 25 and 35 o C) of incubation. Mineral N accumulation was highest at 35 o C in all the treatments and decreased with decrease in temperature of incubation. Nitrogen mineralization potential was higher in soils receiving organic manures while the nitrogen mineralization rate was highest in soil where the use of integrated nutrient management was made. Therefore, the combined use of organic manures along with chemical fertilizers can ensure the sustainable crop yields to meet the food requirements of ever increasing population besides maintaining the soil health.