The changing the biological properties of a forest soil after converting to the paddy field and determining the most sensitive properties to land use change

The evaluation of biologic parameters of soil quality plays an important role in assessing the land management and sustainability of agricultural systems. For this purpose, the biological properties of soil quality, which are sensitive to farming are measured and investigated. The aim of the present study is to evaluate the biological changes forest soil quality after converting to the paddy field and determining the most sensitive properties to disturbance of an ecosystem and the creating a minimum set of data from these parameters using the factor analysis method.

The present study was performed in Poplar research station in Gilan Province. The soil sample collection was done in both natural forest and closest paddy field from five different depth (0-20, 20-40, 40-60, 60-80, and 80-100 cm). The data were analyzed as a factorial test in a completely randomized design with three replications. The factors including the type of land use in two levels and soil depth in five levels were studies in three replications. Therefore, the statistic population of the present study was 10 treatments (5 × 2 =10) with three replications (totally 30 test units). In the study, the microbial respiration, the mineralization percentage of carbon, the microbial biomass carbon, microbial fraction, and the metabolic coefficient of the samples were measured and the sensitivity index to each feature was calculated. The data were analyzed using SAS software. Mean comparison of parameters of Duncan’s test and factor analysis using principal component analysis method were performed.

The results of the study showed that any land use changes from forest to paddy field led to increasing the mineralization percentage of carbon and the metabolic coefficient by 28 and 21% respectively. However, microbial biomass C (61%), microbial respiration (31%), and basal respiration (49%) were reduced. Sensitivity index (SI) indicated that microbial biomass is more sensitive than other parameters to land use. The use of principal component analysis (PCA) showed that two factors could explain more than 70% of the variance in microbial biomass and carbon mineralization percentage and more than 60% of the variance in the amount of carbon mineralization, basal respiration, and a metabolic fraction (quotient). These parameters represent the maximum communality estimation, and the microbial fraction showed the minimum relative importance among the estimates of the total communality values.

The change in land use from forests to the paddy fields had an adverse effect on the biological parameters of soil quality, which led to reducing the soil health and carbon sequestration potential in soil. Therefore, cultivation in these lands exacerbates soil degradation and stopping the process results in longer recovery and resilience time.