Seasonal Changes of Soil Quality Indicators Under Different Cropping Systems in an Arid Environment.

Season and land management are arguably the most influential factors controlling soil quality in arid regions.  Selected physical, chemical and biological soil measurements were assessed for three irrigated cropping systems (continuous cotton, forage alfalfa and matured pecan orchard) near Las Cruces, NM. Soil samples were collected at 0-30 cm soil depth in replicate field treatments during fall, winter, spring and summer of 2015/2016. Soil measurements included the bulk density, available water content, wet aggregate stability, dry aggregate size distribution, soil organic matter, permanganate oxidizable carbon, electrical conductivity, soil pH, sodium adsorption ratio, available phosphorus, nitrate-N, soil extractable cations (potassium, manganese and calcium), and soil micronutrients (copper, iron, manganese and zinc). Results showed that the chemical and biological soil indicators were more affected and exhibited higher seasonal variability under different cropping systems compared to the soil physical indicators which appear to be less variable across the seasons of the year. Soil indicators that varied with season and showed an increase in winter compared to fall across crop management and soil types included bulk density (12.76%), wet aggregate stability (8.60 %) and soil organic matter (35.93 %) respectively. On the contrary, soil indicators that increased in fall compared to winter included permanganate oxidizable carbon (16.50 %), nitrate-N (141.77 %), potassium (16.14 %) and copper (44.94 %) respectively. This study highlights the variations in soil quality indicators that can occur when comparing measurements taken during the different seasons of the year.