Estimates of Dry Matter Yield and Nitrogen Uptake in Sorghum Grown on Saline and Non-Saline Soils Manured with Dhaincha Plant Residues

Abstract

A pot experiment was conducted to determine the effects of manuring with three types of plant residues (roots, shoots and roots plus shoots) of dhaincha (Sesbania aculeata Pers.) on growth of sorghum (Sorghum bicolor L.) grown on saline and non-saline soils. The objectives of this experiment were (1) to determine the effects of adding different plant residues of dhaincha on dry matter yield and nitrogen (N) uptake of sorghum; (2) to estimate the percentages and amounts of N derived from various N sources; (3) to estimate N recoveries from sesbania residues; (4) to make comparison between the direct and indirect 15N tracer techniques for estimating sorghum N uptake from sesbania residues; and (5) to test feasibility of using the non-isotopic technique (N-difference) for estimating N derived from plant residues. For measuring N uptake from various sources, two isotopic dilution techniques were utilized by adding to these soils either 15N-labelled inorganic N fertilizer (indirect method) or 15N-labelled sesbania leaves (direct method). For the indirect method, both soils manured with each type of sesbania residue, received four split applications of 15N-labelled ammonium sulfate. Results indicated that each type of sesbania residue, applied as green manure, resulted in significant increases in both dry matter yield and N uptake of sorghum as compared with the unmanured control. In addition, sesbania residues decreased the harmful effect of salinity on plant growth. Percentages of N derived from residues (%Ndfr) in sorghum grown in non-saline soil ranged between 3.9 and 33%, whereas in saline soil the observed values ranged between 4.9 and 19.8%. The N recoveries in sorghum grown in non-saline soil were 61, 45 and 37% of the total amount contained in sesbania root, shoot and root plus shoot, whereas the values in sorghum grown in saline soils were 48, 14.8 and 15.7%, respectively. The beneficial effects of sesbania residues are attributed not only to the additional N availability to the plants, but also to its effects on the enhancement of soil N uptake. Percentages and amounts of Ndfr calculated using the indirect method were not significantly different from those obtained by the direct method indicating that the indirect method used herein is feasible and simple for measuring N release from organic residues. The findings suggest that the use of Sesbania aculeata residues, particularly the shoots, as green manure, can provide a substantial portion of total N in sorghum. Moreover, the use of sesbania green manure in saline soils, as a bio-reclaiming material, can be a promising approach for enhancing plant growth on a sustainable basis.