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Cropping systems in semiarid regions have frequently relied on continuous tillage and irrigation, but declining groundwater resources have prompted a greater focus on conservation practices to improve soil health and water storage. We compared soil health responses from cotton production systems in semiarid, coarse-textured soils with different crop management strategies under high or low irrigation levels. Management systems included continuous cotton with conventional tillage (CCCT) compared to no-till cotton with a rye cover crop (NTCR) and no-till cotton with a wheat-fallow rotation (NTCW), including high or low irrigation zones within each system. Samples were collected annually from two bulk soil depths (0–10 cm and 10–20 cm) and root-associated soils 7 years after systems were established and continued for 2 years. We found that cropping system, but not irrigation level, altered soil microbial communities and other soil health indicators. Despite variation between study years and sampling zones, the conservation systems had greater soil microbial community size via ester-linked fatty acid methyl ester (EL-FAME or FAME) analysis, extracellular enzyme activities, and soil organic matter than the CCCT system. The NTCW system also had greater arbuscular mycorrhizal fungi FAME abundance. Our study suggests that no-till and conservation strategies such as cover cropping and rotation can improve biological soil health indicators in these sandy semiarid soils even with limited irrigation. [ABSTRACT FROM AUTHOR]

Soil microbial communities in Chihuahuan Desert grasslands generally experience highly variable spatiotemporal rainfall patterns. Changes in precipitation regimes can affect belowground ecosystem processes such as decomposition and nutrient cycling by altering soil microbial community structure and function. The objective of this study was to determine if increased seasonal precipitation frequency and magnitude over a 7-year period would generate a persistent shift in microbial community characteristics and soil nutrient availability. We supplemented natural rainfall with large events (one/winter and three/summer) to simulate increased precipitation based on climate model predictions for this region. We observed a 2-year delay in microbial responses to supplemental precipitation treatments. In years 3-5, higher microbial biomass, arbuscular mycorrhizae abundance, and soil enzyme C and P acquisition activities were observed in the supplemental water plots even during extended drought periods. In years 5-7, available soil P was consistently lower in the watered plots compared to control plots. Shifts in soil P corresponded to higher fungal abundances, microbial C utilization activity, and soil pH. This study demonstrated that 25% shifts in seasonal rainfall can significantly influence soil microbial and nutrient properties, which in turn may have long-term effects on nutrient cycling and plant P uptake in this desert grassland.

Soil C and N have long been recognized as important indicators of soil productivity. The current low levels of soil C and N of cropland soils have led to interest in sequestering C with reduced tillage cropping systems and the Conservation Reserve Program (CRP). Our objective was to assess agroecosystem effects on soft C and N pools in the Southern High Plains. The agroecosystems included three cotton (Gossypium hirsutum L.) cropping systems, CRP land, and native rangeland (NR). We sampled 0- to 5-, 5- to 10-, 10- to 15-, and 15- to 30-cm soil depths at 12 farm sites in five counties in West Texas. Total soil C and N, particulate organic matter (POM) C and N, natural abundance of carbon-13 isotope ([delta][sup.13]C) of POM and of whole soil, potentially mineralizable C and N, water-extractable carbon (WEC), and extractable ammonium (N[H.sup.+.sub.4]) and nitrate (N[O.sup.-.sub.3]) were determined. Total C and N in the 0- to 30-cm soil profile were 34 Mg C [ha.sup.-1] and 2.5 Mg N [ha.sup.-1] for NR, and 23 Mg C [ha.sup.-1] and 1.9 Mg N [ha.sup.-1] for cropland systems, respectively. Total soil C and N in CRP land were greater in cropland soils only in the 0- to 5-cm layer, and were 24 Mg C [ha.sup.-1] and 2.1 Mg N [ha.sup.-1] in 0 to 30 cm. Labile C and N pools were positively correlated with each other and with total soil C and N. Low soft test P may have limited C and N sequestration in CRP land and NR. Improved management practices are needed to sequester C and N in CRP and conservation-tillage cotton systems in the Southern High Plains.