A four year study in a desert land area on the effect of irrigated, cultivated land and abandoned cropland on soil biological, chemical and physical properties

Desert lands occupy vast areas in northwest China and have been undergoing intensive changes in land use. As land uses are considered key drivers of biogeochemical cycles in desert lands, we questioned what effects these changes are having on the biological, physical and chemical properties of the soil. We examined five different land use schemes: (1) natural desert land; (2) abandoned land that was formerly cultivated; (3) barley cultivated land; (4) alfalfa (Medicago sativa) cultivated land; and (5) Astragalus adsurgens cultivated land. The three cultivated lands were irrigated and received fertilizer. Measurements were made after 4 years of annual planting and harvesting or 4 years of cropland abandonment. In previous studies, equivocal results have been reported when examining the effect of land cultivation and land abandonment on soil properties. In the present study, total soil carbon, nitrogen and phosphorus contents increased significantly in the cultivated lands; whereas, they declined in the abandoned cropland when compared to the natural desert land. We concluded that the increase in these parameters in the cultivated fields was most likely due to the irrigation practice, which enhanced the growth of microorganisms and of plants and increased carbon sequestration. The decrease in the abandoned field was most likely due, at least in part, to the relatively short period between the land abandonment and measurements. More time was required for vegetation regrowth and increased carbon sequestration. It is recommended to consider the costs and benefits of carbon sequestration when planning agricultural management practices like growing annual crops and legume forage.