Effects of Green Manures and Zinc Fertilizer Sources on DTPA-Extractable Zinc in Soil and Zinc Content in Basmati Rice Plants at Different Growth Stages

Rice is very sensitive to low zinc (Zn) supply in submerged paddy soils and Zn deficiency is one of the major limiting factors in determining rice production in India. A field experiment was conducted during the summer-rainy seasons of 2009 and 2010 at the research farm of the Indian Agricultural Research Institute, New Delhi, to determine the effects of summer green manure crops and Zn fertilizers on diethylenetriaminepentaacetic acid (DTPA)-extractable (available) Zn concentration in soil and total Zn content in Basmati rice cultivar Pusa Basmati 1 at periodic intervals. Summer green manure crops included Sesbania aculeata (Dhaincha), Crotalaria juncea (Sunhemp), and Vigna unguiculata (Cowpea) and the Zn fertilizers used were ethylenediaminetetraacetic acid (EDTA)-chelated Zn, ZnSO4 center dot 7H(2)O, ZnSO4 center dot H2O, ZnO, and ZnSO4 center dot 7H(2)O + ZnO. Beneficial effects of summer green manure crops and Zn fertilizers on DTPA-extractable Zn concentration in soil and total Zn content in dry matter of Basmati rice at periodic intervals were observed, with significant increases in all the determined parameters, in comparison with those in the control (no Zn application or summer fallow). The rate of increase varied among summer green manure crops and Zn fertilizers during both years. Among the summer green manures, incorporation of S. aculeata led to a significant increase in mean Zn content in Basmati rice grain and straw when compared with C. juncea, V. unguiculata, and summer fallow treatments. Among the Zn fertilizers, significant increases in Zn content in Basmati rice dry matter and DTPA-extractable Zn concentration in soil during various growth stages of the plant were recorded with EDTA-chelated Zn application, followed by the application of ZnSO4 center dot 7H(2)O, ZnSO4 center dot H2O, ZnSO4 center dot 7H(2)O + ZnO, ZnO, and no Zn. The highest mean Zn content in Basmati rice grain and straw was recorded with EDTA-chelated Zn application in 2009 and 2010, respectively. The application of ZnSO4 center dot 7H(2)O was the second best treatment after EDTA-chelated Zn; however, it was statistically inferior to EDTA-chelated Zn. The lowest values were recorded with the control (no Zn application) during both years of study. The amount of Zn concentration in soil was found to be significantly positively correlated with the Zn content in Basmati rice dry matter during both years. Significantly higher levels of residual fertility in soil after the harvest of Basmati rice were observed with application of EDTA-chelated Zn and incorporation of S. aculeata when compared with those of other Zn sources and summer green manures.