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Articles by M.H. Sajjad
Total Records ( 3 ) for M.H. Sajjad
  M.H. Sajjad , H.N. Bhatti , A. Lodhi and F. Azam
  Soil samples amended with powdered plant material of wheat, maize, and sesbania were incubated for 8 weeks at moisture content of 60% of the maximum water holding capacity and 22-26oC for 8 weeks. At 0, 2, 4 and 8 weeks of incubation, portions of soil were analyzed for I) total C and its distribution in humic and fulvic acid fractions and ii) optical properties of humic acid. Humus fractions were extracted with both sodium hydroxide (NaOH) and sodium pyrophosphate (Na4P2O7). Higher amounts of humus C were extracted with NaOH than with Na4P2O7; the treatment differences were more obvious in former. Organic amendment resulted in higher amounts of humic and fulvic acid; more humus C being found in soil amended with maize and wheat. More N was determined in humic acid compared with fulvic acid following the extraction of soil with NaOH. Nature of organic amendment and the extractant used had a significant effect on C/N ratio of humic compounds. Optical density of the humic acid fraction decreased at the increasing wavelength and was correlated significantly with the C content of humic acid. Duration of incubation and nature of amendment had a significant effect on the polymerization and maturity of the humic acid fraction.
  M.H. Sajjad , A. Lodhi and F. Azam
  An incubation experiment was conducted under laboratory conditions to study the changes in some soil enzymes during the decomposition of plant residues. Soil samples amended with powdered plant material of wheat, maize and sesbania were incubated for 8 weeks at moisture content of 60% of the maximum water holding capacity and 22-26°C for 8 weeks. At 0, 2, 4 and 8 weeks of incubation, portions of soil were analyzed for total C and activity of different enzymes. Maximum dehydrogenase and invertase activity was observed for sesbania and minimum in unamended soil, however there was no consistent trends with incubation intervals. Cellulase activity was not affected strongly by organic amendments, however it increased with time in amended than unamended soils. The differences between different treatments were non significant for urease.
  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.
 
 
 
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