Effect of Bio-Organic Additives and Mineral Nitrogen Fertilizer Rates on Nitrogen, Phosphorus and Potassium Uptake by Sorghum with Aid of 15N Stable Isotope

Abstract

A pot experiment was conducted in the green house to evaluate the response of sorghum crop grown on newly reclaimed sand soil to different organic additives in combination with biofertilizer Azotobacter chroococcum and different rates of mineral-N. Straw and root dry weight was stimulated by bacterial inoculation combined with high rate of mineral fertilizer (40 mg N pot-1). Nitrogen uptake by straw and root was gradually increased with increasing fertilizer-N rates. Similar enhancement effect of organic fertilizers and bacterial inoculation was also recognized with high N rate. P uptake by plants was positively enhanced by nitrogen fertilizer application, compost and chicken manure additives. Reversibly, bacterial inoculation has no positive effect on P uptake by either straw or root. Potassium uptake was not varied as affected by organic additives. But, to some extent, it was enhanced by increasing the nitrogen fertilizer rates. Generally, bacterial inoculation has no positive effect on K uptake by either straw or root. Chicken manure was the best in releasing mineralized N (Ndforg) to inoculated plants, followed by leucaena residue then compost. In case of the un-inoculated plants, the release of N from chicken manure surpasses those of compost whereas leucaena residues came to the next. N derived from mineral fertilizer was significantly affected by mineral fertilizer rates and to some extent by organic types. Increases of %Ndff in the uninoculated plants confirmed its dependence mainly on N gained from mineral fertilizer rather than other sources like those derived from organic additives or soil.