Abstract
Improving the soil quality in arid agro-ecosystems requires a greater understanding of how the time-of-sampling and management affect the soil measurements. We evaluated the selected soil quality indicators on samples collected at a 0–0.15 m depth, and at various sampling dates of the year, corresponding to the fall of 2015, winter of 2015/2016, spring of 2016, and the summer of 2016. The three crop management systems sampled included alfalfa (Medicago sativa), upland cotton (Gossypium hirsutum), and pecan (Carya illinoinensis). The soil properties measured included the wet aggregate stability (WAS), mean weight diameter of dry aggregates (MWD), dry aggregates greater than 2 mm (AGG >2 mm), dry aggregates less than 0.25 mm (AGG <0.25 mm), available water capacity (AWC), soil organic matter (SOM), permanganate oxidizable carbon (POXC), soil bulk density (BD), soil electrical conductivity (EC), pH, nitrate-nitrogen (NO3-N), extractable potassium (K), extractable phosphorus (P), calcium (Ca), magnesium (Mg), sodium adsorption ratio (SAR), and micronutrients (zinc, iron, copper, and manganese). Out of the 21 soil measurements, 15 varied significantly with the time-of-sampling within a year, although there were no consistent trends in variability. However, only a few measurements differed significantly with the crop management practices tested. Wet aggregate stability, MWD, AWC, and BD were significantly higher in the summer, while POXC and SOM were significantly higher in the fall and winter, respectively. Soil quality indicators such as NO3-N, K, and P decreased significantly during the spring. This study shows that the seasonal variability of the soil measurements can be significant in the arid agro-ecosystems, with the magnitude of variation depending on the measurement type. The soil managers in the region need to account for this variability, in order to be able to assess the changes in the soil quality. Also, because of the variability that can occur across the different sampling dates within a year, it is advisable to sample during the same period every year, for a consistent interpretation of the directional changes of the soil quality indicators.
Highlights
Soil quality is a crucial component in assessing land sustainability practices in ecosystems [1].The concept of soil quality is rapidly developing and it involves the study of soil responses to management practices, as well as its resilience to natural forces
The soil organic matter (SOM) and permanganate oxidizable carbon (POXC), which are indicators of the soil organic carbon, were the highest in winter and fall, and may have accumulated because of a low soil temperature, lack of soil disturbance that would expose the organic matter to oxidation, and lower microbial activity resulting in less consumption of soil organic products for energy
This pattern agrees with the study conducted by Garcia-montiel et al [29], who indicated that the temporal dynamics in the soil water content follow seasonal cycles of precipitation, and that the water uptake is critical for a short period near the beginning of the rainy season
Summary
Soil quality is a crucial component in assessing land sustainability practices in ecosystems [1]. The concept of soil quality is rapidly developing and it involves the study of soil responses to management practices, as well as its resilience to natural forces. Agriculture 2018, 8, 124 as “the ability of soil to function as a vital living system, within ecosystems and land-use boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health.”. The enhancement and preservation of the soil quality in arid and semi-arid regions is critical for sustaining land productivity under different land uses and management [5]. Seasonal variability in the soil functions and conditions are due to factors such as climate pattern, land use, cropping sequences, and farming systems [6]. Arid and semi-arid regions are characterized by low precipitation rates of 100–250 and 250–500 mm year−1 , respectively, and the development and formation of soils in these regions is affected by water shortage, daily temperature variations, deflations by wind, and reduced microbial activities [7]
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