Tracing in cropped and uncropped soil treated with enriched potassium nitrated and labeled clover residues

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Anne Kamau Muriuki
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Anne Kamau Muriuki
In southeastern USA, legumes are used as green manure to meet crop N requirements by a following crop, but recovery is usually lower than from conventional fertilizers. We conducted a laboratory study to see how well we could account for N applied to soil as ins-labeled KN03 (F), and clover residues (el). Samples of a Typic Kanhapludult soil were incubated with lSN (50 ug n g'ldry soil) from these materials under aerobic conditions. Microbial biomass N, inorganic N, organic N, and potentially mineralizable N (by anaerobic incubation) were monitored for 26wk. Ammonia volatilization from decomposing legume residues was monitored for 12 wk. Inorganic N (NH/, N02' and N03') accumulated and increased in the order Fuel>control (e). Organic N concentration did not differ among treatments. At the end of 26 wk, applied N recovered in soil inorganic N was F: 66%, Cl, 40%; in soil organic N, F: 18% and Cl: 50%; and in microbial biomass N, F: 0.75% and el: 1.5%. Addition of clover residues (e: N ratio =9:1), resulted in rapid initial mineralization, but K1SN03 addition resulted initially in immobilization. Microbial biomass N did not differ among treatments, but recovery of applied N in microbial biomass was significantly greater (P<0.05) in Cl than F throughout incubation. We assumed that applied N not found in the measured N pools was denitrified: F, 16% and el, 10%. The anaerobic incubation-extraction procedure underestimated the size of potentially mineralizable N pool by a factor of 3 in e1 and 4 in e (P<0.05).