Evolution of Soil Structure and Fertility After Conversion of Native Sandy Desert Soil to Irrigated Cropland in Arid Region, China

Abstract

Assessment of soil quality and its direction of change with time is a primary indicator of sustainable agricultural land management. In this study, the temporal changes in soil physical and chemical properties were determined after conversion of native desert soils to irrigated croplands in a marginal oasis of the arid region, northwest China. Soil samples were collected from seven closely located farm fields that had been cultivated for 3, 5, 10, 14, 23, 30, and 40 years after agricultural cultivation, from adjacent remnant uncultivated sandy land (0 year), and from farm fields in an old oasis cultivated for more than 50 years. All the soils in the study were Psamments that derived from the deposition of aeolian sand. After cultivation, significant changes in particle size distribution and aggregate size distribution and stability in the 0-to 20-cm surface soil only occurred in soils cultivated for more than 10 years, showing a consistently increasing pattern with increasing duration of cultivation. The result indicated that soil did not contain enough coarse aggregates to control wind erosion, suggesting the need to maintain residues on the soil surface to aid wind erosion control for these newly cultivated sandy soils. As cultivation time increased, soil organic carbon (SOC), total and available N and P, cation exchange capacity, and CaCO 3 concentrations all increased. Soil organic carbon and total N concentrations increased by 6.4 times and 5.9 times, respectively, after 40 years of continuous cropping. The increased silt and clay content caused by irrigation with silt-laden river water plays an important role in the aggregate formation and SOC and nutrient accumulation and retention. The results also indicated that the evolution of desert soil toward the sustainable agricultural soil requires at least 50 years. The absolute amounts of soil aggregate, SOC, and nutrients are still low after 40 years of cropping and were insufficient to support sustaining crop production. Therefore, improved land management such as conservation tillage and crop and grass rotation is imperative to accelerate soil structure and fertility improvement and maintain long-term productivity of the farmlands.

Cultivation effects on the carbon and nitrogen dynamics at depth in oasis farmlands of the Southern Tarim Basin, China

“…However, the obvious increase occurred at 0-20-, 20-40-and 40-200-cm depths in 80-and 100-year farmlands. The sequestration of SOC and TN in the topsoil was also observed in other oasis farmlands in northwest China (Su et al 2010;Li et al 2010;Xu et al 2011), but was contrary to the result observed by Lobe et al (2001) who found that prolonged arable cropping leads to severe SOC loss in dry regions with sandy soils in the South African Highveld, and reached equilibrium after 34 years, but the loss continued if the cropping was prolonged even after almost 100 years. Generally, ecosystem C sequestration is determined by the law of mass conservation and the availability of key nutrient elements, such as N or P (Hessen et al 2004;Kirkby et al 2011).…”

“…In addition, Su et al (2010) and Li et al (2013) observed that the potential for soil carbon storage and fertility improvement in the process of desert soil cultivation were controlled to a large extent by silt and clay contents. In the present study, the irrigation water from the Cele river contains much silt and clay with 4.23~5.45 g SOC kg −1 and 0.25~0.37 g N kg −1 during flood season (Shi and Gong 1995).…”

“…The decrease of SOC sequestration in 30-year farmland and the increase in 100-year farmland were suggestive of this issue. Similarly, Su et al (2010) suggested that the evolution of desert soil toward sustainable agricultural soil requires at least 50 years. This has important implications for sustainable land management in the area.…”

Multi-scale variability of soil carbon and nitrogen in the middle reaches of the Heihe River basin, northwestern China

“…The fertilizer type and fertilization rate also contribute considerably to soil C and TN levels in cropland. According to the conventional cultivation custom, approximately 516 kg N ha −1 and 86 kg P 2 O 5 ha −1 are applied during the maize growing season, including one base fertilization of urea and di-ammonium phosphate and three topdressings of urea later in Gaotai (Li et al, 2009 , 60-90 kg K 2 O ha −1 and 3-6 t ha −1 farmyard manure in cropland of Linze each year (Su et al, 2010b and 21 g N kg −1 are applied each year (Su et al, 2006). Application of organic manure combined with mineral fertilizers has been shown to be effective in increasing both TN and the labile and recalcitrant pools of topsoil OC under conventional management (Su et al, 2006;Yang et al, 2007;Zhou et al, 2013).…”

“…Li et al (2009) found that crop rotations increased SOC and TN densities by 30-65% and 61-64%, respectively, in the 0-30 cm soil during the 10 years of cultivation after the desert was transformed into irrigated cropland. The SOC and TN contents in the topsoil of sand-fixing shrubs, irrigated cropland and shelter forest increased with time after the reclamation of desert land (Su et al, 2007(Su et al, , 2010a(Su et al, , 2010b. Su et al (2009) reported that SOC and TN accumulated at rates of 0.4 Mg C ha −1 year −1…”