| Pak. J. Bot., 39(5): 1751-1761, 2007. | Back to Contents | ||||
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Updated: 09-07-09 | ||||
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SEASONAL CHANGES IN SOIL MICROBIAL BIOMASS NITROGEN UNDER AN IRRIGATED WHEAT-MAIZE CROPPING SYSTEM TARIQ MAHMOOD*, REHMAT ALI, FAQIR HUSSAIN, KAUSER ABDULLA MALIK AND GHULAM RASUL TAHIR
Abstract: Seasonal changes in soil microbial
biomass nitrogen (Nmic) were followed under an irrigated
wheat-maize cropping system receiving urea and/or farmyard manure (FYM)
at 0–200 kg N ha–1 year–1 for the past ten
years. The Nmic was maximum (109–218 kg N ha–1)
at the wheat stem elongation stage and minimum (80–148 kg N ha–1)
at the wheat tillering stage. Fertilizer application significantly
increased the Nmic, indicating that the belowground processes
were limited by N availability. Averaged across sampling dates, the Nmic
ranged from 93 kg N ha−1 (in unfertilized) to 176 kg N ha–1
(in FYM applied at 32 t ha–1 year–1), whereas the
annual Nmic flux ranged from 57 kg N ha–1 (in
unfertilized) to 118 kg N ha–1 (in FYM applied at 16 t ha–1
year–1). Crop dry matter and N yields increased due to
fertilizer application. At an equivalent N application rate, urea
applied alone produced maximum yields, followed by urea combined with
FYM, whereas FYM applied alone yielded minimum. The size and flux of Nmic
were poor indicators of the crop N availability, whereas the soil
mineralizable N determined by alkaline permanganate method at the crop
sowing stage was significantly correlated with the soil mineral N, and
with the crop dry-matter and N yields.
Nuclear
Institute for Agriculture & Biology, Jhang Road, Faisalabad-38000,
Pakistan
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