Saturday, 15 July 2006

Relationship between Various Soil Organic Matter Pools with Nitrogen Uptake by Wheat.

A.P. Gupta, Dept of Soil Science, CCS Haryana Agricultural Univ, C-432, Nirman Vihar, Vikas Marg, Delhi, 110 092, India and Ranjan Laik, Dept of Soil Science, Rajendra Agricultural Univ, Pusa, Samastipur, Bihar, India.

Long-term fertility experiments may develop considerable amount of mineralisable nutrients, which also contribute to the nutrition of a crop. The main sources of the mineralisable nutrients are the labile soil organic matter pools, which decompose within a few weeks or months and contribute to plant nutrition. It is all the more important to know the role of labile soil organic matter pools in supplying nutrients to a crop. The three labile forms, which were considered for the present study, are Dissolved Organic Carbon (DOC), Microbial Biomass Carbon (MBC) and Light Fraction Carbon (LFC). A long-term field experiment was selected which has been running at the research farm of Department of Soil Science, CCS Haryana Agricultural University since October 1967 to study the contribution of various labile pools of SOM to wheat nutrition. The soil was classified as Coarse Loamy Typic Ustochrept. The cropping sequence followed since the inception of the experiment is pearl millet-wheat. The experiment consisted of 3 doses of FYM at 15, 30 and 45 Mg ha-1 applied in three modes i.e. in summer to pearl millet, in winter to wheat and in both summer and winter seasons. One FYM control was also maintained. These ten treatments were assigned in main plots and each main plot was divided into three subplots receiving N at 0, 60 and 120 Kg N ha-1. The experiment was replicated four times. Soil samples were collected from plots receiving N at 0 and 120 kg ha-1. Nitrogen uptake increased with increasing application of FYM and fertilizer N. All the three labile forms of soil organic matter had a significant relationship with the nitrogen uptake of wheat. The R2 values for the relationships between Dissolved Organic Nitrogen (DON), Microbial Biomass Nitrogen (MBN), and Light Fraction Carbon (LFC) with nitrogen uptake were 0.63, 0.58 and 0.72 respectively. The values show the strength of the labile fractions to supply nitrogen during the wheat growth period. The maximum values of DON, MBN and LFC obtained from the quadratic equations for maximum nitrogen uptake were 91.67 mg L-1, 43 mg kg-1 and 0.3% respectively. These results indicate that the DOC, MBC and LFC contribute to the nutrition of wheat crop because of their quick mineralization during the wheat growth.

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