Amidst intensifying global agricultural water demand, optimizing management practices and understanding the role of soil amendments, particularly biochar (BC), in modulating soil water dynamics are critical. Here, we review the potential impacts of BC on soil water dynamics, elucidate mechanistic underpinnings, and identify critical research gaps and prospective avenues. In general, BC modifies soil structure, hydraulic properties, surface albedo, and heat fluxes, which influence soil water storage, energy balance, and irrigation paradigms. Depending on soil texture and BC properties, BC demonstrates a greater reduction in bulk density and saturated hydraulic conductivity in coarse-textured soils compared to fine-textured soils. BC application generally increases water holding capacity (WHC) while exhibiting no consistent impact on soil water infiltration. Increased WHC of soils results from increased porosity, surface area, and soil aggregation. Increased porosity arises from a confluence of factors, encompassing new pores formation, reorganization of pores, increased soil aggregation, dilution effects of BC, reduced soil compaction, and biotic interactions, including increased population of burrowing invertebrates. BC tends to increase plant-available water in coarser soils, attributed to its hydrophilic nature, augmented specific surface area, and enhanced overall porosity. However, BC may induce soil water repellency, contingent upon variables such as feedstock composition, pyrolysis temperature, and specific soil attributes. While BC exhibits transformative potential in enhancing soil hydraulic properties, scalability concerns and economic viability pose challenges to its widespread agricultural application. Overall, BC offers promising avenues for sustainable water management. However, it is imperative to explore large-scale applications and conduct long-term field studies across different management, climate, and soil types to fully understand how different types of BC impact soil water dynamics. Graphical Abstract

While fertilizers are vital for food production, their environmental and health impacts require continual advancement. This study explored new micronized sulfur-containing nitrogen fertilizers (UREA-ES) that offer potential benefits compared to traditional options. The objective was to understand the transformation and loss pathways of UREA-ES, such as 40-0-0-13 (UREA-ES40) and 11-0-0-75 (UREA-ES11) in two different soils. This study evaluated the transformation and loss pathways of nitrogen (N) from the above fertilizers with and without urease (UI) and nitrification (NI) inhibitors in comparison to urea. Results of the study showed that the UREA-ES fertilizers had lower and delayed ammonia (NH₃) volatilization compared to urea treatment (UREA). The use of UI with UREA-ES fertilizers reduced NH₃ volatilization losses more effectively than UI with UREA, indicating potential synergies between UI and sulfur (S). The hydrolysis of UREA-ES fertilizers was slowed down by the UI under both acidic and alkaline conditions, similar to UREA fertilizer. The coating of UREA-ES fertilizers with UI + NI significantly delayed NH₄ ⁺ nitrification. Coating UREA-ES fertilizers with UI or UI + NI delayed nitrate leaching losses, indicating prolonged N availability in the soil. These results were corroborated by a greenhouse sorghum study where UREA-ES fertilizers with UI or UI + NI led to higher total N uptake and higher grain yield than UREA fertilizer with UI or UI + NI. UREA-ES fertilizers also resulted in higher total S uptake by sorghum, indicating improved S nutrition. Overall, the study revealed UREA-ES fertilizers had significantly improved total N uptake by sorghum and had significantly higher grain yields, especially at lower N application rates due to decreased N losses. Both UI and NI showed potential benefits for UREA-ES fertilizers compared to traditional UREA, including reduced NH₃ volatilization losses, delayed nitrate formation, and enhanced N uptake by plants, resulting in increased grain yields, especially at the lower N application rate (75 kg N ha⁻¹).

High soil moisture due to frequent excessive precipitation can lead to reductions in maize grain yields and increased nitrogen (N) loss. The traditional methods of computing N status in crops are destructive and time-consuming, especially in waterlogged fields. Therefore, in this study, we used unmanned aerial vehicle (UAV) remote sensing to evaluate the status of maize under different N rates and excessive soil moisture conditions. The experiment was performed using a split plot design with four replications, with soil moisture conditions as main plots and different N rates as sub-plots. The artificial intelligence SciPy (version 1.5.2) optimization algorithm and spherical function were used to estimate the economically optimum N rate under the different treatments. The computed EONR for CRS 2022 was 157 kg N ha⁻¹ for both treatments, with the maximum net return to N of USD 1203 ha⁻¹. In 2023, the analysis suggested a lower maximum attainable yield in excessive water conditions, with EONR pushed up to 197 kg N ha⁻¹ as compared to 185 kg N ha⁻¹ in the control treatment, resulting in a lower maximum net return to N of USD 884 ha⁻¹ as compared to USD 1019 ha⁻¹ in the control treatment. This study reveals a slight reduction of the fraction of NDRE at EONR to maximum NDRE under excessive water conditions, highlighting the need for addressing such abiotic stress circumstances when arriving at an N rate recommendation based on an N-rich strip concept. This study confirms the importance of sensing technology for N monitoring in maize, particularly in supporting decision making in nutrient management under adverse weather conditions.

Alfalfa (Medicago sativa L.) requires a large amount of potassium (K) for maintaining forage yield and stand persistence. Therefore, soil inherently low in K levels must be supplemented with K fertilizers. Although several commercial K fertilizers are available on the market, choosing an appropriate K-supplementing source for a particular soil can be crucial in boosting alfalfa yield and nutritive value. A two-year study was conducted in an arid southern New Mexico location near Tularosa to evaluate the efficacy of three K commercial fertilizer sources in improving alfalfa yield and nutritive value in a moderately low potassium (84 ppm) soil. Nine K treatments or combinations and a no-K control were tested in a randomized complete-block design with four replications. Overall, supplementation of 160 kg ha⁻¹ of K₂O in all treatments resulted in a significant increase in alfalfa seasonal forage yield and nutritive value compared to the control. Sulfate of potash combined with ammonium sulfate (AS) produced greater seasonal yield compared to other fertilizers (muriate of potash and potassium nitrate) or combinations with gypsum (p < 0.05). This treatment combination also showed greater crude protein, neutral detergent fiber, tissue Fe and S, and soil residual sulfate-S and nitrate-N. A positive correlation between sulfur abundance and nitrogen availability in alfalfa production was evident in the study. Addition of AS to all three K fertilizers yielded better seasonal forage yield than K fertilizers alone or K fertilizers in combination with gypsum. Adding gypsum to the K-fertilizers appeared to have negative effect on the seasonal forage yield. Future research should evaluate various combinations of the levels of K and S to determine the most reasonable balance.