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Articles by M.H. Sajjad
Total Records ( 3 ) for M.H. Sajjad
  F. Azam , M.H. Sajjad , A. Lodhi and R.M. Qureshi
  Experiments were conducted under greenhouse conditions to study I) the dynamics over time of mineral N, mineralizable N and humus N during decomposition in soil of leguminous and non-leguminous plant material and ii) the impact of these changes on growth and N nutrition of wheat fertilized with 15N-labelled ammonium sulphate. Finely ground straw of wheat, maize and sesbania was allowed to decompose in soil for 0, 2, 4 and 8 weeks. Sub-samples of soil were analyzed for the content of mineral N, mineralizable N and humus N. The bulk soil was sown to wheat and the plants harvested at maturity. Nitrogen as 15N-labelled ammonium sulphate was applied in two split doses of 40 and 60 mg kg-1 soil. Accumulation of mineral N in soil during 8 weeks of residue decomposition was found to depend on the chemistry of plant residues, more mineral N being released in soil amended with plant residues with narrow C/N ratio i.e., maize and sesbania. These residues also contributed more to humus N and maintained a higher content of potentially mineralizable N. Wheat straw not only caused a net immobilization of N during 8 weeks of aerobic incubation but a substantially higher loss of NO3¯+NO2¯ -N during subsequent incubation under submerged conditions. The loss of NO3¯+NO2¯ -N was more where residues were given less time for decomposition. Plant residues applied immediately before sowing wheat or those allowed shorter period of decomposition had a negative effect on plant growth. Of the three residue types, wheat straw caused a higher reduction in plant growth. This was attributed mainly to significantly reduced availability to plants of soil-N, while uptake of fertilizer N was affected almost similarly by the three types of residues. Residues of maize and sesbania had a positive effect on grain yield and total biomass of wheat. As a whole, ca 30% of the fertilizer N applied was taken up by the plants and >40% was unaccounted in the soil-plant system, fertilizer N remaining in soil being <30% of the applied. Relatively higher proportion of the applied N remained in amended than unamended soil after crop harvest.
  M.H. Sajjad , F. Azam and A. Lodhi
  Laboratory and greenhouse experiments were conducted to study the changes in mineral N, humus N and plant available N during following decomposition of plant residues (wheat straw, maize straw and sesbania straw) for different time periods. Accumulation of mineral N in soil was found to depend on the chemistry of plant residues, more mineral N being released in soil amended with plant residues with narrow C/N ratio i.e., maize and sesbania. These residues also contributed more to humus N and maintained a higher content of potentially mineralizable N. Wheat straw not only caused a net immobilization of N during 8 weeks of aerobic but a substantially higher loss of NO3 +NO2 -N during anaerobic incubation. The loss of N under these conditions appeared to depend on the length of time the residues were allowed to decompose in the soil, more losses being recorded for residues at early stages of decomposition. Undecomposed or partially decomposed plant residues had a negative effect on plant (wheat) growth; the effect was positively related to N uptake by plants. The negative effect was eliminated by increasing the time of residue decomposition to 8 weeks at which point maize and sesbania had a positive effect on grain yield and total biomass of wheat. Since N availability could be the main yield determining factor, sufficient time for residue decomposition will be required to achieve net N mineralization and thus improved plant growth especially for plant residues with a wide C/N ratio. However, the N released during aerobic incubation (or during land preparation prior to planting) may indeed be lost at first irrigation from the soil-plant system depending upon the content of easily oxidizable organic C.
  F. Azam and M.H. Sajjad
  External heating of soil samples following addition of dichromate is a commonly used method for the determination of organic carbon (C). We have successfully standardized microwave oven as a source of external heating for reliable and quick determination of organic C in soil samples by colorimetric method. Ten soils varying in C content were collected from agricultural fields differing in physico-chemical and other characteristics. The method involves: I) addition of 8 mL of conc. H2SO4 and 5 mL of 2N K2Cr2O7 solution to soil samples containing ca 5 mg C and placed in 100 mL glass beakers, ii) heating the treated samples in a microwave oven with rotating plate, iii) dilution of the contents of the beaker to 50 mL with distilled water, iv) determination of optical density of the samples at 590 nm, v) calculations for C content against a glucose standard (5 mg C mL-1 solution; 1.25 g glucose 100-1 mL) treated like the samples. The newly developed method gives values of C lower than those obtained with the conventional colorimetric method and Walkley-Black method. However, almost perfect correlations existed between the values obtained by the three methods. Regression equations thus developed can conveniently be used for the accurate measurement of organic C in soil samples. Time of heating in microwave oven that varied from 45 to 120 sec did not have a significant bearing on the amount of C determined. Hence, heating for 60 sec can conveniently be adopted for routine analysis. The proposed method is not only quick but highly economical in terms of energy used in heating the samples.
 
 
 
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