Effect of Different Management of Wheat and Sugar Beet Residues on Some Chemical and Biological Properties of Soil

Excessive application of chemical fertilizers can lead to poor soil and groundwater quality and severe nutritional disturbances on the land and environmental damage. In recent years, increasing concern about the production of healthy food and the emphasis on maintaining fertility and soil quality have led to more attention to maintaining and increasing soil organic matter through appropriate management practices. Management of crop residues can play pivotal role in improving soil productivity and quality as well as crop yield through its effects on soil physical, chemical and biological properties. Soil quality, generally, indicates the ability of the soil to function as an ecosystem by preserving fertility, environmental quality and enhancing the health of plants and creatures which is always under the influence of management operations. Hence, soil quality assessment methods allow quantitative biological, chemical and physical responses of soil to be compared to different management practices. Soil quality assessment is a very complicated process due to the different soil properties in different management conditions. To investigate the effect of various managements of wheat and sugar beet residues on some chemical and biological properties of soil, two distinct experiments were carried out in a completely randomized design with three replications. Treatments of first experiment included control (CW), wheat residues retained on soil surface (W), wheat residues incorporated into soil with plowing (PW), wheat residues incorporated into soil with plowing plus urea fertilizer (PFW), wheat residues burnt (BW) and wheat residues burnt is followed by incorporating into soil with plowing (PBW). Treatments of second experiment were including control (CS), sugar beet residues retained on soil surface (S), sugar beet residues incorporated into soil with plowing (PS) and sugar beet residues incorporated into soil with plowing plus urea fertilizer (PFS). In W and S treatments, the remained plants were distributed uniformly throughout the plot. In PW and PS treatments, the remained plants were mixed with soil by plowing to a depth of 30 cm. In PFW and PFS treatments, plant residues with urea fertilizer (4 tons per hectare) were added to soil surface and then plowed. In BW treatment, wheat plant residues were distributed uniformly in plot and then the burning was performed manually. In BPW treatment, plant residues were mixed with soil after burning by plowing. After applying the experimental treatments, all plots were irrigated in the same way. Irrigation intervals were applied to the plots similar to the adjacent plots and were irrigated regularly during the experiment period. After 6 months of application of the treatments, sampling of the treatments was carried out using a systematic method, consisting of plowing depth (0 to 25 centimeters of soil). Results showed that various managements of wheat and sugar beet residues caused significant changes in studied chemical (except pH) and biological properties. All management methods, except retention of residues on soil surface (C and S treatments), increased organic carbon, total nitrogen, available phosphorus and potassium compared with the control treatment. Generally, in both crop residues, the greatest content of organic carbon, total nitrogen and available potassium were related to incorporating residues into soil with plowing plus urea fertilizer (PFW and PFS treatments). Also, the highest content of available phosphorus was related to PBW and PFS treatments in wheat and sugar beet residues management, respectively. In the case of basal microbial respiration and microbial biomass carbon, the most effective managements were residues incorporation into soil with plowing (PW and PS treatments) and then residues incorporation into soil with plowing plus urea fertilizer (PFW and PFS treatments). In this study, although residues burning (BW and PBW treatments) improved nutrient content, microbial respiration and microbial biomass carbon compared with the control treatment, they were less effective than PW and PFW treatments. According to the results, in both wheat and sugar beet residues, the most appropriate managements to improve the soil quality indicators were to incorporate the residues into soil with plowing plus urea fertilizer, as well as only incorporating the residues into soil with plowing. The results showed that the use of a minimum set of properties affecting soil quality or MDS can determine the soil quality with reasonable accuracy and cost and time less in the studied soil.