Effect of wheat residue enriched with Streptomyces and urea on available phosphorus and some soil microbial characteristics in laboratory conditions

Soil as a living system is one of the factors affecting the balance of the ecosystem and many processes, especially on a small scale, take place in it. Soil microorganisms play an important role in maintaining soil quality through decomposition of organic material and nutrient cycling. The use of microorganisms in ecosystems whose biological community stability has been severely compromised due to high consumption of fertilizers, salinity and chemical toxins, is to improve the efficiency of nutrient consumption and biological control of pests and diseases. Soil organic matter increases soil microbial activity. On the other hand, enrichment of organic matter with microorganisms increases their nutrients release. To understand the vital role of soil microorganisms in the release and storage of energy and nutrients in the soil, in recent years, increased attentions has been paid to the estimation of microbial biomass in the soil. Therefore, the aim of this study was to investigate the effect of urea, Streptomyces inoculation and wheat straw on available phosphorus, microbial respiration, microbial biomass C, metabolic coefficient and microbial biomass turnover time.

This study was conducted under controlled laboratory conditions. A factorial experiment with two levels of urea (0 and 1.6 g/100g wheat straw), two levels of Streptomyces sp. (0 and 5%) and wheat straw treatments (0 and 1%, w/w) was conducted using a completely randomized design with three replications. Wheat straw was treated with the urea fertilizer and Streptomyces sp. inoculum firstly and the treated straw was then thoroughly mixed with the soil. The mixtures were incubated at 25±2 ° C for 90 days. Microbial biomass C and available phosphorus were measured monthly for three months and microbial respiration was measured weekly. To revive the microbial population, the containers were pre-incubated at room temperature for two weeks and soil moisture was adjusted to about 70% of the field capacity.

Streptomyces inoculation, addition of wheat straw and urea increased available phosphorus concentration, respiration and soil microbial biomass C. In this experiment, the amount of respiration and microbial biomass C with the simultaneous addition of Streptomyces, wheat straw and urea to the soil was the highest and the effect of Streptomyces inoculation on wheat straw on the studied parameters was more than the two other factors. The lowest amount of microbial respiration, microbial biomass C and phosphorus was in control soil (without urea, Streptomyces and wheat straw). Addition of wheat straw to the soil increased microbial respiration and microbial biomass C by providing the required substrate. Also, the use of wheat straw and urea led to an increase in soil available phosphorus.

The results of this study showed that in carbon-restricted soils, the use of plant residues enriched with Streptomyces and urea increased microbial respiration and microbial biomass carbon in the soil. Also, wheat plant residues addition to the soil increased the soil available phosphorus. Treatment of soil with Streptomyces also increased soil available phosphorus, which was more perceptible in the plant residues enriched with Streptomyces. The results show that the simultaneous application of plant residues, urea and Streptomyces, has increased soil microbial activity. Therefore, in carbon-restricted soils, increasing the level of organic matter and its enrichment can lead to increased microbial activity and biological potentials in the soil.Keywords: Microbial biomass C, Microbial respiration, Plant residue, Streptomyces, Urea