Short-Term Effects of Mushroom Substrate Compost on Penetration Resistance, Aggregate Size Distribution and Their Stability in Soils with Different Textures

Adding organic matter to the soil is an important method to solve the problem of compaction and consequently penetration resistance and fertility reduction. Mushroom substrate compost (MSC) has many properties that are required for growing organic crops and environmental management. Considering that the ingredients of mushroom substrate compost (including heavy soil, light soil, root soil, wheat straw and stubble, limestone and chicken manure) are different from other types of organic materials, it is necessary to carry out new research to investigate its effect on the physico-chemical properties of the soil. Although different textures behave differently but, the effect of MSC on the penetration resistance and aggregates size distribution in different soils, has not been studied, so far. Therefore, the purpose of this study was to investigate the short-term effect of MSC on the penetration resistance, mean weight diameter of aggregates, aggregates size distribution and organic matter content in three soil types.

A factorial experiment was conducted in a completely randomized design with three replications. Factors consist Soil texture at three levels (sandy loam, loam and clay) was the first factor, and MSC at three levels (0, 3 and 6% W/W) was the second factor. After treatment of the soils, samples were then incubated for 120 days, and they were saturated and dried with urban water, regularly, once a month (saturated from above), during this period. At the end of the incubation period, disturbed and undisturbed soil samples were taken by 5 cm in diameter and 4.5 cm in height steal cylinders. The penetration resistance was measured by a micro-penetrometer on the core samples at the matric suction of 0.3 bar. Organic matter, mean weight diameter of aggregates and aggregates size distribution were measured.

The results showed that the use of 6% level mushroom substrate compost in the sandy loam soil caused a decrease in the penetration resistance compared to the level of 3% and the control, due to the interaction between the compounds in the compost and the creation of stable soil aggregates. Also, the results showed that highest amount of organic matter and mean weight diameter of aggregates at 6% level of MSC was found in loam texture. Also, the order of the mass of aggregates in classes 4-8 and 2-4 mm, was in loam> sandy loam> clay, with significant differences between the textures. Application of MSC at 3 and 6% levels in the loam texture significantly increased the mass of aggregates of 0.25 – 0.5 and 0.5-1 mm in comparison with control. These aggregates did not show significant differences in sandy loam and clay soils at different application levels of the MSC Organic matter, mean weight diameter of aggregates, mass of aggregates of 0.5 to 1, and 0.25 to 0.5 mm increased in the range of 27 to 66%, 16 to 34.5%, 4 to 117.5% and 4 to 170%, respectively, by increasing MSC application levels at different soils. Conclusion This compost is different from other modifiers and can have different effective mechanisms in different textures. The simultaneous addition of lime, clay and organic matter (through compost) to soils with different textures causes cation exchange reactions in the soil. Lime as one of the main additives that has the ability to improve the behavior of fine-grained soils has been noticed for a long time. In this way, in clay and loam soils, the interaction between lime and clay with organic matter plays an important role as soil accumulation factors by forming cationic bridges. The use of lime and gypsum directly improve soil resistance. Therefore, the use of mushroom substrate compost in agricultural lands is useful for improving the soil structure.