Variations of Soil Fertility Following the Oak Deforestation in Miankooh Region, Shahrekord

Land-use change has been extensively considered by farmers as an easily available approach with the aim of finding new resources for producing more agricultural products. Deforestation, the most common type of land-use change, has led to the extensive parts of productive lands in different parts of the world being highly degraded. Rainfed farming can be listed as one of the most important substitutes for the forests which have been destroyed. In this scenario, as time goes on, the productivity of the land might be decreased due to the problems arising out of inappropriate land management strategies or inexorable climate changes, leading to the lands being abandoned. Given the prevalence of this issue in the Southwest part of Iran, the present study aimed to monitor the changes of selected soil fertility properties following the oak deforestation in the Miankooh region, Southwest Shahrekord City.  

The study area is located in 31° 44′ N and 50° 34′ E, 150 kilometers far from Shahrekord City, Southwest Iran. The area has a semi-arid climate with an annual average temperature and rainfall of 16.3 °C and 439.5 mm, respectively. This area is naturally covered with semi-dense oak forests, considerable parts of which have been partly destroyed and then assigned to rainfed wheat by local farmers. A substantial loss in crop yield in recent decades, mainly due to the decreased precipitation, has persuaded the young farmers to abandon the less productive lands. Aimed at assessing the impact of land-use change on soil fertility, a total of 30 surface soil samples (0–25 cm) were collected from the lands under wheat cultivation, semi-dense oak forest, and abandoned lands. The soil samples were air-dried and sieved through a 2-mm sieve and then analyzed for soil pH, organic matter content (OM), total nitrogen (N), available phosphorus (P), and exchangeable potassium (K) using standard methods. The data was statistically analyzed applying the Duncan test at the probability level of 5%, one-way ANOVA, and the multivariate approach of the Hotelling test.

The studied soils contained a fairly high content of clay and can be classified as alkaline soils, possibly due to their relatively high content of calcium carbonates. A high soil buffering capacity caused by the accumulation of calcium carbonates in surface layers would have contributed to enabling the studied soil to undergo different uses without any significant changes in soil pH. Following the land-use change from oak forest to rainfed wheat and then to abandoned (uncultivated) lands, soil organic matter and total nitrogen decreased from 2.33% and 0.11% to 1.0% and 0.05%, respectively. This observation may be arisen out of the fact that the soils under wheat cultivation receive a relatively deep plowing almost every year, which can substantially reduce the percentage of soil total N or OM by mixing the rich surface layer of the soil with the less enriched subsurface layer. As far as the abandoned soil is considered, receiving the negligible inputs of organic matter caused a further decrease in soil total N and OM. The investigated soils benefited from acceptable amounts of available P so that the insignificant fall in their P contents due to land-use change may not affect their fertility potential. When it comes to K, unlike soil OM and N, it significantly rose from 615.0 mg/kg in forest lands to 633.4 in the soils under wheat cultivation. It appears that the addition of manure to surface soil by local farmers has provided a good source of this important nutrient. Applying the multivariate approach of the Hotelling test aimed at simultaneous comparing of different land-use types according to all of the studied soil properties, it was observed that the three types of land use investigated could be considered as different units.

Even though deforestation generally leads to soil degradation, some soil fertility properties might remain unchanged or even be improved based on the management strategies applied. In fact, applying purposeful and appropriate techniques in the field may be helpful to alleviate the unavoidable consequences of land-use change. Compared to substituting the semi-dense oak forests with rainfed farming, abandoning the croplands may result in more problematic soils. The pretty fast degradation of the crucial soil fertility properties caused by land-use change gives a serious warning about the possibility of further destruction of soils in the area studied, which may make them entirely unsuitable for any kind of agricultural use. Considering the complexity of soil environment, comparing the soils under different land use in terms of each individual soil property may not necessarily lead to reliable results. Accordingly, multivariate approaches, like the Hotelling test, maybe more consistent with the complex nature of the soil.