Seasonal variations in nitrogen transformations in some soils from two different agro-ecological zones in Morogoro

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University of Dar es Salaam
Seasonal variations of various forms of nitrogen in soils representing two different agro-ecological zones in Morogoro Region (Melela and Tandai) were studied by sampling soils at different seasons. These soils were analyzed for Total N, available N, and organic N fractions (Total, ammonium, amino acid, hexosamine, hydroxylamine, identified). Available N varied widely with season and constituted only a small portion (less than 4%) of total n. the pattern and magnitude of seasonal variations were different in the two zones studied and appeared to be related to soil moisture. Acid hydrolysis studies revealed that Total hydrolysable-n, unhydrolyzable-N and ammonium, amino acid, hexosamine, hydroxymine, identified and unidentified N fractions, expressed as percentages of Total soil N, varied with season, but the variations were different for different fractions. Throughout the experiment period, amino acid-N accounted for the largest portion of the identified-N fraction whereas hydroxymine-N constituted the smallest proportion. The findings of the present study suggest that any chemical method of assessing the availability of N to crops based on the determination of only one form of N will prove unsatisfactory. It is suggested that while formulating N management programmes for Melela and Tandai, various forms of n and their patterns of seasonal variations be put into consideration. Studies on N gains and losses from soil leading to the drawing up of Nitrogen Balance Sheets for the different agro-ecological zones, and the different cropping systems, and studies on the nature of the readily mineralizable forms of organic N are suggested as areas of further research which would be useful in formulating sound N management programmes.
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Soils, Nitrogen content, Nitrogen, Agricultural research, Morogoro, Tanzania (region)
Byabachwezi, J.M (1985) Seasonal variations in nitrogen transformations in some soils from two different agro-ecological zones in Morogoro, masters dissertation. University of Dar es Salaam. Available at (