Abstract
In order to monitor spatial inorganic N concentrations in soils over time, collected soil samples are composited and thoroughly mixed. The sticky characteristic of Vertisol when wet makes it difficult to thoroughly mix wet samples. There is the need for appropriate drying of Vertisol samples to facilitate thorough mixing and storage to retain mineral N content reflective of field status. We determined the effects of drying method, storage period and C:N ratio on inorganic N contents of tropical Vertisols. The treatments comprised of three soils with different C:N ratios, five drying methods inclusive of a check (method 1), and five storage periods including a check (period 1). Storage temperature was -10°C. In method 1, field-fresh soil samples were kept at -10°C and later used for mineral N extraction using 0.5 M K2SO4. Period 1 involved storing soil samples for two days from sampling date before mineral N extraction. Ammonium-N and NO3 -N were determined using colorimetric method. Method 1 x period 1, for each soil, resulted in NH4+-N and NO3--N contents significantly different from other treatments indicating that extraction for mineral N should be done on field moist soil not later than two days after sampling. Key words: Drying method, mineral nitrogen, storage period, soil preparation, Vertisols
Highlights
Nitrogen (N) is the plant nutrient element most limiting to crop performance in the majority of soils in the tropics (Bekunda et al, 2007)
In order to monitor the net effects of N dynamics in soils over time, composite soil sample is collected at time intervals, covering the entire period during which the N changes are to be determined
The sticky characteristic of Vertisol when wet makes it difficult to thoroughly mix wet composite samples to obtain a representative sample of an area, determination of inorganic N content of Vertisols over a period of time would require some adequate drying of samples to facilitate thorough mixing and storage, but both the drying temperature and the length of storage period have effects on soil extractable nutrients (Houba and Novozamsky, 1998; Magesan et al, 2002; Gray and Mclaren, 2003)
Summary
Nitrogen (N) is the plant nutrient element most limiting to crop performance in the majority of soils in the tropics (Bekunda et al, 2007). In order to monitor the net effects of N dynamics (that is, inorganic N concentrations) in soils over time, composite soil sample is collected at time intervals, covering the entire period during which the N changes are to be determined. The sticky characteristic of Vertisol when wet makes it difficult to thoroughly mix wet composite samples to obtain a representative sample of an area, determination of inorganic N content of Vertisols over a period of time would require some adequate drying of samples to facilitate thorough mixing and storage, but both the drying temperature and the length of storage period have effects on soil extractable nutrients (Houba and Novozamsky, 1998; Magesan et al, 2002; Gray and Mclaren, 2003). We determined the effects of drying method, storage period and C:N ratio on inorganic N contents of tropical Vertisols
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