Influence of inorganic and organic sources of nutrition and crop rotation on yield of groundnut and castor

A field experiment was conducted for five years to study the effect of crop rotation with a legume and judicious use of organic and inorganic fertilizers for minimizing the dependency on inorganic fertilizer under rainfed conditions. The experiment waslaid out with three sets of experiments consisting of annual rotation of groundnut-groundnut, castor-castor and groundnut-castor. Different nitrogen management treatments were imposed on castor in castor-castor rotation and groundnut-castor rotation. The nitrogen management treatments include different combinations of organic manures (compost and glyricidia loppings) and inorganic fertilizer (urea). The results revealed that legume effect of groundnut on castor was observed in all the years. Growth, yield attributes and yield of castor were significantly higher when the complete dose of nitrogen was applied either through inorganic fertilizer or with a different combination of organic and inorganic forms than control in castor-castor rotation. Highest seed yield of castor in castor-castor rotationwas recorded when 100% N was applied as urea in first four years of experimentation. The response of castor to urea was higher during high rainfall years. Advantage of organic manures was observed after 4 years and highest seed yield of castor was recorded during fifth year where nitrogen was supplied as 50% N as glyricidia loppings + 50% N as inorganic and which was at par with 100% N as compost but significantly superior than 100% N as urea in castor-castor rotation. Residual effect of N applied to castor was not observed on pod yield of groundnut except in one year out of five years.