Abstract
Medium-term changes in the labile nutrient pool of microbial biomass carbon (MBC) and nitrogen (MBN) resulting from organic manure application in rice (Oryza sativa L.)-based triple cropping systems have been poorly studied. Therefore, the effects of organic materials on the soil physico-chemical properties and microbial biomass in rice fields were investigated at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh, from April 2010 to December 2012. Five treatments (control, cow dung, poultry manure, rice straw, and chemical fertilizer) were laid out in a randomized complete block design with four replications. The organic residues (2 t C ha-1) were applied 7 days before transplanting and were combined with inorganic fertilizers, following integrated plant nutrition systems. This paper presents the results from the last of the five consecutive rice growing seasons. All of the organic residues increased the pH, and organic C, N, P, and K contents of the soil. However, poultry manure was more efficient in increasing soil fertility than cow dung and rice straw, resulting in a significant increase in P from 22 mg·kg-1 to 63 mg·kg-1 at crop harvest. All of the organic residues also increased the soil water holding capacity and decreased bulk density. Furthermore, poultry manure resulted in significantly higher microbial biomass C (432 mg·kg-1; P < 0.05) and N (31.60 mg·kg-1; P < 0.05) levels in the soil at crop harvest, followed by cow dung and rice straw. These findings indicate that the regular application of organic residues and manures will help to enhance soil fertility and production sustainability.
Highlights
The soil microbial biomass (SMB) indicates the ecological and biological quality and fertility of the soil, and is affected by organic/inorganic fertilizer application [1]
These findings indicate that the regular application of organic residues and manures will help to enhance soil fertility and production sustainability
The SMB is involved in soil biogeochemical processes in soil-water-plant systems [1] [2], driving the nutrient cycle in agro-ecosystems, and playing a vital role in soil nutrient transformations and acting as a labile nutrient pool that is available to plants [3] [4]
Summary
The soil microbial biomass (SMB) indicates the ecological and biological quality and fertility of the soil, and is affected by organic/inorganic fertilizer application [1]. SOC may take a very long time to increase [5] [6] and observation of SOC changes alone may not explain the effect of organic matter on nutrient availability via microbiological activities. Soil microbial biomass, which measures changes in both SOC and total soil nitrogen (TSN), can be used as a management indicator for soil fertility and crop productivity [7]. The effects of the various influencing factors, such as climatic and edaphic factors, fertilizer use, and crop establishment practices, on SMB are difficult to quantify due to their interactions; and estimation of the spatial and temporal distribution of SMB on the basis of limited field observations are even more difficult [4] [8]
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