Growth, Nitrogen and Phosphorus Uptake of Sorghum Plants as Affected by Green Manuring with Pea or Faba Bean Shell Pod Wastes Using 15N

Abstract

Background: During the freezing or canning preparation process of green grain leguminous, large amounts of shell pods are considered as agricultural organic wastes, which may be used as Green Manure (GM) for plant growth enhancement. Objective: Evaluation of the effectiveness of soil amended with shell pod wastes of pea (PGM) or faba bean (FGM) as GM on growth, nitrogen and phosphorus uptake in sorghum plants. Methods: Determination of the impact of adding four rates of nitrogen (0, 50, 100, and 150 kg N ha-1) in the form of pea (PGM) or faba bean (FGM) shell pod wastes as GM on the performance of sorghum using the indirect 15N isotopic dilution technique. Results: Sorghum plants responded positively and differently to the soil amendments with either GMs used, particularly, the PGM. In comparison with the control (N0), soil amendment with an equivalent rate of 3.5 t ha-1 of PGM (PGM100) or with 6.5 t ha-1 of FGM (FGM150) almost doubled dry weight, N and P uptake in different plant parts of sorghum. Regardless of the GM used, estimated values of %Ndfgm in sorghum plants ranged from 35% to 55% indicating that the use of pod shells as GM provided substantial portions and amounts of N requirements for sorghum. Moreover, nitrogen recoveries of added GM (%NUEgm) ranged from 29 to 45% indicating that N in both of GM forms were used effectively. Accordingly, equivalent amounts to 17 - 48 kg N ha-1 of inorganic fertilizer may be saved. The beneficial effect of incorporating pod shells in soil on sorghum N was mainly attributed to their N availability, besides to their effects on the improvement of soil N uptake, particularly when using PGM. Conclusion: The agricultural by-products of faba bean and pea pod shells could be used as GM for sorghum growth improvement by enhancing N and P uptake from soil and from the organic source.