Browsing by Author "P.B. Jha"

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Dynamics of viable nitrifier community and nutrient availability in dry tropical forest habitat as affected by cultivation and soil texture
(Kluwer Academic Publishers, 1996) P.B. Jha; J.S. Singh; A.K. Kashyap
Seasonal dynamics of N-mineralization and the size of the viable community of nitrifying bacteria were studied for a forest site and an adjoining cropland site. The forest site was dominated by Boswellia serrata and Acacia catechu in the tree layer, and by Nyctanthes arbortristis and Zizyphus glaberrima in the shrub layer. Crop sequence on the cropland site was Oryza sativa/Lens culinaris. The soil type in both the sites was ultisol (USDA). The cropland soil had significantly higher bulk density, and clay content but lower organic C, total N and total P than forest soil. The soil moisture content, numbers of ammonia- and nitrite oxidizing bacteria and N- mineralization rates were highest in the wet season and lowest in the dry season, while the size of mineral N and P pools showed a reverse trend in both sites. The numbers of free-living cells of ammonia- and nitrite oxidizing bacteria were significantly related with each other as well as with the soil moisture content and N-mineralization rates. In N-mineralization, NO3/- was the dominating form in the forest site during rainy season, while in other seasons in this site and in all the seasons in the cropland site, NH4/+ -N was predominant. The N-mineralization rate and the number of viable nitrifying cells were consistently higher for the forest soil compared to the clay-rich cropland soil. The combination of low soil organic matter and high clay content suppressed the number of free-living cells of nitrifying bacteria and N-mineralization rates in the cropland site.
Effect of fertilizer and organic matter inputs on nitrifier populations and N-mineralization rates in a dry tropical region, India
(1996) P.B. Jha; A.K. Kashyap; J.S. Singh
The study was conducted in a dryland farm, which was under Oryza sativa (rainy season)/Lens esculenta (winter seasons) crop rotation, to assess the size of viable community of ammonia- and nitrite-oxidizing bacteria and N-mineralization, as affected by season and inputs of chemical fertilizer and organic matter. Six treatments with three replicates were established in completely randomized block design. The treatments were: control, chemical fertilizer, wheat straw (WS), WS + fertilizer, farmyard manure (FYM) and FYM + fertilizer. The effects of treatments and seasons on NH+4-N, NO-3-N and PO-4-P pools were significant, but treatment X season interaction was not significant. The mineral N pools had a dry season maximum, while N-mineralization and nitrification rates were highest during rainy season and lowest during summer season. Differences in N-mineralization and nitrification rates due to treatments were significant. The N-mineralization rates were greatest in fertilizer and fertilizer + WS (or FYM) treatments and the nitrification rate was highest in the fertilizer treated soil. Analysis of pooled data of all treatments showed that N-mineralization rate was positively related with soil moisture and inversely with the size of mineral N pools. The numbers of viable cells of ammonia- and nitrite-oxidizing bacteria were related significantly to each other, and were highest during the rainy season and lowest in the summer season. The effect of treatments, except for the fertilizer-alone treatment, on the most probable number counts of the nitrifying bacteria was not statistically significant.