Changes in attributes of soils subjected to fallow in desertification hotspot

ABSTRACT Soils in semi-arid regions have been degraded by overgrazing, which reduces the production capacity and, in certain situations, leads to desertification. An alternative to recover degraded areas is the fallow period, which works through the resilience of the soil itself, increasing the supply of organic matter and improving soil physical properties. Thus, the objective of this study was to test the hypothesis that 14-year grazing exclusion improves soil physical and chemical attributes in degraded areas under desertification. The study was conducted in Irauçuba, Ceará State, Brazil. The experimental design was completely randomized, in a 4 x 2 factorial scheme corresponding to four areas and two managements (overgrazing and fallow), with four replicates, plus an area with native vegetation (reference), with characteristics of secondary vegetation. Fallow led to improvements in soil physical and chemical attributes after 14 years; however, in comparison to the study conducted in the same area with a 7-year fallow period, there were few alterations. Organic carbon content was higher in fallow areas than in overgrazing areas, and the fraction in highest proportion was the mineral-associated organic carbon.摘要 半干旱地区土壤因过度放牧发生退化，不仅降低土壤生产能力，在特定情况下甚至会引发荒漠化。恢复退化区域的有效途径之一是实施休耕期管理，其借助土壤自身的恢复力提升有机质供给量，并改善土壤物理性状。据此，本研究旨在验证下述假说：14年禁牧可改善荒漠化退化区域的土壤理化属性。本研究于巴西塞阿拉州艾劳苏巴（Irauçuba）开展。试验采用完全随机设计，设置4×2析因试验方案，涵盖4个样区与2种管理模式（过度放牧与休耕），设置4次重复；另设置一处带有次生植被特征的原生植被区域作为参照样地。14年休耕后，土壤理化属性得到改善；但与该区域此前开展的7年休耕研究相比，本次研究仅观测到少量变化。休耕样区的有机碳含量高于过度放牧样区，其中占比最高的有机碳组分是矿质结合态有机碳。