Cover cropping is commonly acknowledged to promote soil health in agriculture. However, contradictory findings on the benefits of cover crops for soil health, crop productivity, economic and ecological factors, as well as the influence of inherent soil parameters on such benefits exist in the scientific literature. Here, we critically assessed evidence of cover crop benefits through a systematic review of the published literature. To access relevant papers, we searched the literature for cover crops and soil health indicators using Scopus (1996-2020), ScienceDirect (1996-2020) and Google scholar (1970-1996) with specific keywords and combinations. Only English research papers including experimental plots and control groups were considered. We analyzed 102 unique peer-reviewed papers and 1494 corresponding unique plots encompassing various cover crops, soil textures, climates, management systems and experimental duration (1-3 years, 4-6 years, 7-10 years and over 10 years). Strong evidence suggests that cover crops can enhance soil structure and promote soil health by improving soil physical and chemical properties, including saturated hydraulic conductivity (mean net change of 105.6 %), total organic carbon (10.1 %), and total nitrogen (20.2 %). On the other hand, cover crops exhibit weak effects on properties like bulk density and microporosity with fairly low values of net change. In most cases, cover crops increase the soil carbon content, including microbial biomass carbon (19.5 %) and particulate organic carbon (49.5 %). In this systematic review, we found limited studies on the effect of cover crops on soil health as influenced by soil texture, regional climate, rainfall and duration of the cover crop practices. The paucity of long-term regional systematic research of soil physics, chemistry and biology makes it difficult to forecast future implications of cover crops on soil health indicators.

Soil water repellency can substantially alter hydrologic processes, particularly the ability of soils to infiltrate water. Water repellency often changes through time, making it difficult to simulate infiltration behaviors of water‐repellent soils using standard models. Here, we propose a simple rate‐based correction term that starts with a value of zero at the beginning of the infiltration process (t = 0) and asymptotically approaches 1 as time increases, thus simulating decreasing soil water repellency through time. The correction term can be used with any infiltration model. For this study, we selected a simple two‐term infiltration equation and then, using two data sets of infiltration measurements conducted in soils with varying water repellency, compared model error with versus without the added term. The correction substantially reduced model error, particularly in more repellent soils. At the same time, the rate constant parameter introduced in the new model may be useful to better understand dynamics of soil water repellency and to provide more consistent interpretations of hydraulic properties in water‐repellent soils.

Biochar is purported to provide agricultural benefits when added to the soil, through changes in saturated hydraulic conductivity (K_sat) and increased nutrient retention through chemical or physical means. Despite increased interest and investigation, there remains uncertainty regarding the ability of biochar to deliver these agronomic benefits due to differences in biochar feedstock, production method, production temperature, and soil texture. In this project, a suite of experiments was carried out using biochars of diverse feedstocks and production temperatures, in order to determine the biochar parameters which may optimize agricultural benefits. Sorption experiments were performed with seven distinct biochars to determine sorption efficiencies for ammonium and nitrate. Only one biochar effectively retained nitrate, while all biochars bound ammonium. The three biochars with the highest binding capacities (produced from almond shell at 500 and 800 ^∘C (AS500 and AS800) and softwood at 500 ^∘C (SW500)) were chosen for column experiments. Biochars were amended to a sandy loam and a silt loam at 0 % and 2 % ($w/w$ ), and K_sat was measured. Biochars reduced K_sat in both soils by 64 %–80 %, with the exception of AS800, which increased K_sat by 98 % in the silt loam. Breakthrough curves for nitrate and ammonium, as well as leachate nutrient concentration, were also measured in the sandy loam columns. All biochars significantly decreased the quantity of ammonium in the leachate, by 22 % to 78 %, and slowed its movement through the soil profile. Ammonium retention was linked to high cation exchange capacity and a high oxygen-to-carbon ratio, indicating that the primary control of ammonium retention in biochar-amended soils is the chemical affinity between biochar surfaces and ammonium. Biochars had little to no effect on the timing of nitrate release, and only SW500 decreased total quantity, by 27 % to 36 %. The ability of biochar to retain nitrate may be linked to high micropore specific surface area, suggesting a physical entrapment rather than a chemical binding. Together, this work sheds new light on the combined chemical and physical means by which biochar may alter soils to impact nutrient leaching and hydraulic conductivity for agricultural production.

Low-cost, accurate soil water sensors combined with wireless communication in an internet of things (IoT) framework can be harnessed to enhance the benefits of precision irrigation. However, the accuracy of low-cost sensors (e.g., based on resistivity or capacitance) can be affected by many factors, including salinity, temperature, and soil structure. Recent developments in wireless sensor networks offer new possibilities for field-scale monitoring of soil water content (SWC) at high spatiotemporal scales, but to install many sensors in the network, the cost of the sensors must be low, and the mechanism of operation needs to be robust, simple, and consume low energy for the technology to be practically relevant. This study evaluated the performance of a resistivity–capacitance-based wireless sensor (Sensoterra BV, 1018LE Amsterdam, Netherlands) under different salinity levels, temperature, and soil types in a laboratory. The sensors were evaluated in glass beads, Oso Flaco sand, Columbia loam, and Yolo clay loam soils. A nonlinear relationship was exhibited between the sensor measured resistance ($\Omega$) and volumetric soil water content (θ). The $\Omega$–$\theta$ relationship differed by soil type and was affected by soil solution salinity. The sensor was extremely sensitive at higher water contents with high uncertainty, and insensitive at low soil water content accompanied by low uncertainty. The soil solution salinity effects on the $\Omega$–$\theta$ relationship were found to be reduced from sand to sandy loam to clay loam. In clay soils, surface electrical conductivity (EC_s) of soil particles had a more dominant effect on sensor performance compared to the effect of solution electrical conductivity (EC_w). The effect of temperature on sensor performance was minimal, but sensor-to-sensor variability was substantial. The relationship between bulk electrical conductivity (EC_b) and volumetric soil water content was also characterized in this study. The results of this study reveal that if the sensor is properly calibrated, this low-cost wireless soil water sensor has the potential of improving soil water monitoring for precision irrigation and other applications at high spatiotemporal scales, due to the ease of integration into IoT frameworks.

Soil texture can affect soil temperature, soil moisture, the protection of organic material against microbial degradation, and other soil properties. All these factors potentially influence net nitrogen (N) mineralization. The objective of this analysis is to investigate the relationship between soil texture and net N mineralization using different approaches, including a 10‐week laboratory incubation of undisturbed soil cores from 47 sites in California, modeling, and a meta‐regression analysis of 461 datasets from 20 studies. In the laboratory incubation as well as in the meta‐analysis, total soil N increased significantly with increasing clay content. Net N mineralization expressed in mg kg ⁻¹ soil did not change significantly with increasing clay content, but significantly decreased when expressed as a proportion of total soil N. These results are most likely explained by physical and chemical protection of organic molecules by clay minerals. Protection in turn led to the observed increase in total soil N over time. Based on the incubation and measured bulk densities, net N mineralization in the top 15 cm of the soil profile was 30% higher in a sandy loam compared to a clay soil. Model simulations indicated that texture‐related differences in soil temperature and moisture have only a small effect on net N mineralization in irrigated agricultural fields under Mediterranean conditions.