Pak. J. Bot., 37(1): 105-117, 2005. | Back to Contents | ||||
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Updated: 09-07-09 | ||||
SEASONAL CHANGES IN SOIL MICROBIAL BIOMASS CARBON UNDER A WHEAT-MAIZE CROPPING SYSTEM RECEIVING UREA AND FARMYARD MANURE IN DIFFERENT COMBINATIONS TARIQ MAHMOOD*, REHMAT ALI, FAQIR HUSSAIN AND GHULAM RASUL TAHIR
Abstract: Seasonal changes in carbon (C) availability and soil microbial biomass
carbon (Cmic) were studied under an irrigated wheat-maize system receiving
urea at 50 or 100 kg N ha-1 year-1 in combination with 8 or 16 t ha-1
year-1of farmyard manure (FYM). Treatment effects on Cmic were not
visible during the wheat growing season, whereas fertilizer application
significantly increased Cmic during the maize growing season. In unfertilized
soil, Cmic was similar under two crops, whereas fertilized soils showed
11-56% higher Cmic under maize than under wheat. Under both crops, C
availability, as assessed by aerobically mineralizable C (AMC) and total
organic C, was generally higher in fertilized soils than in the unfertilized.
Fertilized soils showed much higher AMC under wheat than under maize;
the stimulatory effect being much more pronounced due to increasing
application rate of FYM than that of urea. In fertilized soils, but
not in the unfertilized, specific respiratory activity (SRA) of soil
microbial biomass was twice higher under wheat as compared to that under
maize. Results suggested that the soil microflora under wheat was probably
dominated by 'r-strategists', which respired more C as CO2 than that
incorporated into microbial biomass. In contrast, 'k-strategists' dominated
under maize, incorporating relatively more C into their biomass than
that respired as CO2. Fertilizer application significantly increased
Cmic turnover rate; while increasing the FYM application rate further
increased the turnover rate, the increasing urea level had no effect.
The overall high Cmic turnover rate, particularly in fertilized soils
(1.69-2.29 year-1) indicated that nutrient cycling through soil microbial
biomass may be substantial under agro-climatic conditions prevailing
in this region.
Nuclear Institute for Agriculture & Biology, P.O. Box 128, Jhang
Road, 38000 Faisalabad, Pakistan. |
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