Effect of Sesbania,Azolla and rice straw incorporation on the kinetics of NH4, K,Fe, Mn,Zn and P in some flooded rice soils |
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Authors: | S Nagarajah H U Neue M C R Alberto |
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Institution: | (1) Department of Soils, The International Rice Research Institute, P. O. Box 933, Manila, Philippines;(2) Present address: Division of Agricultural Chemistry, Central Agricultural Research Institute, Gannoruwa, Peradeniya, Sri Lanka |
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Abstract: | In a greenhouse study, with and without rice plants, of five flooded Philippine rice soils whose organic C (OC) content varied
from 0.5 to 3.6%, incorporation ofSesbania rostrata, Azolla microphylla and rice straw affected the kinetics of soil solution NH
4
+
−N, K+, Fe2+, Mn2+, Zn2+, and P. Sesbania and Azolla increased NH
4
+
−N concentration above the control treatment, whereas rice straw depressed it. In all soils Azolla released less NH
4
+
−N than Sesbania. The apparent net N release depended on the soil and ranged from 44–81% for Sesbania and 27–52% for Azolla.
These effects persisted throughout the growth of IR36. Soil solution and exchangeable NH
4
+
−N increased initially but levelled off between 30 to 80 days and between 20 to 40 days after flooding (DF), respectively.
With rice, soil solution NH
4
+
−N concentration, reached a peak at 15–40 DF and declined to very low levels (<4mg L−1). In the 3 soils of low OC content nitrogen derived from green manure ranged from 34–53% and the apparent revovery of added
green manure N varied from 29–67%. Almost all N released from both Azolla and Sesbania were recovered in the rice plant in
all soils except Concepcion with only 77%. The concentration of K+, Fe2+, Mn2+ and P in the soil solution were higher with rice straw than Sesbania and Azolla in all soils except Hanggan which showed
no change in Fe2+ and Mn2+ but increased K+ and P. In general, rice straw, Sesbania and Azolla decreased Zn2+ concentration in all soils. |
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Keywords: | Azolla flooded soil green manure N recovery kinetics of NH4 K Fe Mn Zn P N immobilization N release Sesbania rostrata soil solution NH 4 + − N |
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