Seasonal changes in soil ammonium and nitrate in relation to crop production
2002
Paibool Wivutvongvana(Chiang Mai University, Chiang Mai (Thailand). Faculty of Agriculture. Dept. of Soil Science and Conservation) E-mail:[email protected] | Suchart Jiraporncharoen(Chiang Mai University, Chiang Mai (Thailand). Faculty of Agriculture. Dept. of Soil Science and Conservation) E-mail:[email protected]
Twelve on farm experiments (sites) were conducted throughout the Thai Family Research Project area in four provinces (three sites per province) during 2001 growing season. Upland rainfed corns (Zea mays L.) were planted on Typic Calciustolls soil in Lopburi, whereas lowland paddy rices (Oryza sativa L.) were grown on Typic Tropaquepts in Chachoengsao and on Aeric Paleaquults in Buriram and Sisaket. The main purpose was to investigate seasonal changes in soil exchangeable NH4+ and NO3- in relation to farmers conventional practices of fertilization (F) and a control modified treatment (C). The amount of fertilizer in the C was approximately half of the F plot. Except only one site of corn, monthly concentrations of exchangeable NH4+ and NO3- at two soil depths (0-20 and 50-70 cm) were not significantly different between the C and F treatments. For corn, soil NH4+ varied slightly during the growing period whereas concentrations of NH4+ in paddy soil increased considerably depending upon soil fertility after planting (soil submergence) and then decreased gradually until rice harvest. Concentrations of nitrate, particularly under flooded rice soil depleted rapidly after flooding. In addition to soil fertility and cultivation practices, seasonal changes in soil NH4+ and NO3- concentrations were closely related to plant uptake (hence planting date, moisture availability and plant growth performance). Considering the very low concentrations of NH4+ and NO3- in the flooded water as well as in both the upper and lower soil depths, the application methods and fertilizer rate used in the present investigation were unlikely to have any adverse effect on the environment.
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