**Preface to "Agroecological Approaches for Soil Health and Water Management"**

Soils provide the foundation for food production, soil water and nutrient cycling, and soil biological activities. With land use and land cover changes over the last century, soil fertility depletion, greenhouse gas emissions, irrigational water scarcity, and water pollution have threatened agricultural productivity and sustainability. An improved understanding of biochemical pathways of soil organic matter and nutrient cycling, and microbial community involved in regulating soil health and soil processes associated with water flow and retention in soil profile helps design better agricultural systems and ultimately support plant growth and productivity. This book, Agroecological Approaches in Soil and Water Management, presents a collection of original research and review papers studying physical, chemical, and biological processes in soils and discusses multiple ecosystem services, including carbon sequestration, nutrients and water cycling, greenhouse gas emissions, and agro-environmental sustainability. The 15 chapters in this book cover various topics related to soil organic matter and nutrient cycling, soil water dynamics, and related hydrological processes across multiple soils, climate, and management. Several chapters highlight the impacts of land use, landscape position, and land-cover change on soil health and plant productivity. It also has chapters on greenhouse gas emissions as affected by agricultural management, roles of soil amendments like biochar and micronutrients. Novel water management strategies, including the use of coalbed methane co-produced water, biodegradable hydrogels, and livestock-integrated cropping to improve soil health are also discussed. The book further incorporates modeling studies on yield and greenhouse gas emissions and presents a review of sustainable agricultural and water management practices.

Soil microbial communities are sensitive to adopting sustainable management practices. Chapter 1 (Coller et al., 2021) investigates the response of soil living communities to change in farming practices from integrated pest management to organic orchard management in northeastern Italy. This study highlights agricultural strategy that could impact the edaphic community within the first few years of land management transition. While fungi responded quickly to the changes, bacteria and microarthropods had lesser impacts from management and higher from abiotic factors. Landscape positions also affect soil properties, and crop production. Chapter 2 (Sun et al., 2011) presents the effects of landscape positions and types on soil properties and the chlorophyll content of citrus. Soil nutrient content was higher in the footslope and terraces and lower in the upperand mid-slope positions. However, citrus chlorophyll content was higher in the middle and upper landscape position compared to the footslope. Chapter 3 (Ojha et al., 2021) studied the effect of different landscape positions (ridge, midslope, and valley) on total soil carbon (TC), total nitrogen (TN), and carbon-nitrogen (CN) ratio, and soil pH in a mountainous district in central Nepal. The isotopic signature of the natural abundance δ13C and δ15N were used to identify the source of C and N. Valley soil had higher TN, CN, and soil pH values than the ridge and midslope soils. Further, the valleys had more positive δ15N signatures than ridge and midslope, indicating higher inorganic and organic N fertilizer inputs compared to other landscape positions. Therefore, Chapters 2 and 3 suggest the possibility of improving soil quality and agricultural sustainability through targeted land management measures. In line with this study, Khokhar et al. (2021) in Chapter 4 reported the effect of land slopes and maize and cowpea strip-intercropping on productivity and soil erosion in the Shivalik foothills in northwest India. Results indicated significantly higher maize and cowpea yield on a 1% and 2% slope than on steeper slopes. Runoff, soil, and nutrient losses were lower on 1% and 2% slopes than on 3% slopes. The study suggested the adoption of a strip-intercropping system with a 4.8 m maize strips and 1.2 m cowpea strips resulted in 24% more yield over sole maize and cowpea, increased net return, and reduced runoff and soil loss by 10.9%, and 8.3%, respectively, than sole maize crop.

The impact of changes in land management on soil and environmental quality depend on land-use history. Ren et al. (2020), in Chapter 5, reported an increase in soil N2O emissions following forestland conversion to cropland in a subtropical Southwest China. The conversion leads to an increase in the annual cumulative N2O flux by 76–491%. N2O emissions from croplands with tillage and fertilization were 94% and 235% higher than those from croplands with tillage and no fertilization, in the short-term and long-term, respectively. The relative contribution of fertilizer and tillage was different. Fertilization increased N2O emissions by 63% and 84% in the short-term and long-term, while tillage contributed to 37% and 16% increased emissions in the short-term and long-term. Chief factors affecting N2O emissions were soil NO<sup>3</sup> , NH<sup>4</sup> <sup>+</sup> availability, and water-filled pore spaces. Tillage disturbs soil structure and increases soil aeration to facilitate soil organic N mineralization. Further, mineral N fertilization will lead to an increase in soil NO<sup>3</sup> and NH<sup>4</sup> <sup>+</sup> availability. Chapter 6 (Mahmud et al., 2021) reviews different pathways of N losses such as ammonia volatilization (NH3), nitrous oxide (N2O) emissions, and nitrate leaching (NO3), and suggests potential mitigation strategies such as fertilizer placement, best management practices, livestock management, use of carbon-rich sources, growth-promoting microbial consortia, organic farming, crop diversification, genetic improvements, and site-specific nutrient management for improving agricultural sustainability. The role of livestock on soil health is discussed in Chapter 7 (Dahal et al., 2021). This chapter highlights complex interrelationships between different soil health indicators in pasture lands with inorganic or broiler litter fertilization history. Results discerned a strong positive relationship of active carbon (POXC) with N and potentially mineralizable N, indicating the ability of active carbon fraction to influence nitrogen cycling dynamics. Information on POXC appears highly valuable in determining optimum nitrogen fertilizer recommendations for sustainably managing grazing systems and improving soil health properties.

Biochar has been increasingly considered an ecological tool for soil health and water management. Ayaz et al. (2021) reviewed the implications of using biochar as a soil amendment on soil health and crop productivity in Chapter 8 and suggested improvements in soil physical, chemical, hydrological, and microbial properties with biochar application, the magnitude of impact varying with biochar type, climate, and soil management. Chapter 9 (Yu et al., 2021) studies the effect of corn straw biochar application on soil and water losses during the spring thawing period in northeast China. Biochar application at rates 6 and 12 kg m–2 increased soil saturated water content by 24.17 and 42.91% and field capacity by 32.44 and 51.30%, respectively. An increase in biochar application rate was translated into decreased runoff and soil erosion. Biochar application can reduce soil and water losses in sloping farmlands.

Another ecological approach to soil and water management is discussed in Chapter 10 (Cechm ˇ ankov ´ a et al., 2021). This chapter evaluated the impact of a novel, biodegradable hydrogel on ´ soil chemical and hydrological properties. The hydrogel had a positive effect on soil water-holding capacity and the availability of nutrients under controlled settings. For example, 3% whey-based hydrogel application increased the available level of phosphorus and potassium by up to 50 and 84%, respectively. While the gel appears to be promising for soil amendment, field experiments and studies on plant health and growth attributes may prove beneficial. These innovations are more important in water-limited environments. Chapter 11 (Poudyal and Zheljazkov, 2021) studies another innovative approach for water management using coalbed methane co-produced water (CBMW). This study evaluated various blending ratios of CBMW with fresh water on the yield and quality of alfalfa and oat forages. While irrigating forages with different levels of blending increased soil pH and sodium adsorption ratio, there was no significant effect on the nutritive value of both forages. Long-term studies are needed to fully understand the soil and agronomic effects of CBMW and biodegradable hydrogel.

Soil organic matter, major nutrients, and key physical and chemical properties are often emphasized while discussing soil health in agroecosystems. However, Chapter 12 (Thapa et al., 2021) reviews the effects of micronutrients on soil health and soybean production in the Midwest USA. The studies reported inconsistent soil health and yield response; several factors like climate, soil pH, cultivar, irrigation, soil organic matter, and application type (foliar vs. band) influenced plant and soil response to micronutrients. More long-term field studies are necessary to understand better the management of micronutrients for soil health and productivity.

Biogeochemical and process-based models provide a broader perspective on sustainability and resilience. Chapter 13 (Jiang et al., 2021) discusses soil organic carbon and rice yield in Kunshan, China, under variable water and carbon management using a modified Denitrification Decomposition (DNDC) model. The authors used four future climate scenarios (RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5) to understand soil organic carbon under climate change scenarios. Climate scenarios significantly affected rice yield but not soil carbon. For example, rice yield decreased by 18.41%, 38.59%, 65.11%, and 65.62% for all RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5 scenarios, respectively the 2090s. There was a minimal effect of irrigation and conventional fertilizer application on soil carbon irrespective of RCP scenarios. However, controlled irrigation with straw returning appears to increase both SOC and rice yield in long-term simulation. Chapter 14 (Hang et al., 2021) uses the carbon footprint method to calculate greenhouse gas emissions in a circular farm's planting and breeding system modules. Further, a multi-objective linear programming model is used in determining the optimal structure and scale of growing crops and raising farm animals in circular agriculture in relation to economic and environmental impacts and farm waste utilization. Results showed that greenhouse gas emissions occurred primarily from manure management in the livestock industry. After optimization, agriculture income increased by 64%, and greenhouse gas emissions increased by only 12.3%. Indeed, carbon reduction measures must rely on measures for optimizing the management of manure and adjusting feed structures within the circular agricultural framework.

Finally, the benefits and trade-offs of different sustainable practices, namely conservation agriculture, crop diversification, organic farming, and agroforestry, adopted in Europe and North Africa, are discussed in Chapter 15 (Choden and Ghaley, 2021). While adoption of such practices could increase crop yield, soil and water conservation, and sustainable food production to ensure food security, it largely depends on local conditions and their effectiveness for farmers. As such, investment in crop-system modeling is deemed necessary.

The chapters are primarily compiled to help and motivate students, researchers, scientists, land managers, and policymakers in environmental science, soil science, agronomy, hydrology, and water resources. The book will be useful for anyone interested in soil health and water management across the globe. The editors acknowledge and thank the authors, reviewers, and editorial assistants for their help, support, contribution, and enthusiasm. Any error in facts, data, and interpretation remains the sole responsibility of the authors.
