Biochar effects on soil properties and sweet corn production under deficit irrigation in a semi-arid environment

Date
2022-12
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Abstract

Water scarcity is a major challenge for agriculture. Considering the growing food demands of the increasing population, a major part of agricultural research is engaged in improving the water use efficiency (WUE) of irrigated agriculture and conserving water without yield penalties. Deficit irrigation (DI) is a direct water conservation approach of decreasing water application to improve WUE. The DI has been extensively researched in several crop species, including vegetables. Owing to the shallow root systems and sale of vegetable produce on a fresh weight basis, vegetable crops are relatively more sensitive to moisture stress than field crops. In this context, additional drought-adaptive strategies in combination with DI can be used to sustain vegetable productivity and quality. Biochar, a high-carbon coproduct of pyrolysis of organic matter, is suggested as a soil amendment to mitigate drought stress and is being explored as additional practice with DI to minimize the yield losses due to water deficits. In Chapter 1, we reviewed the effects of biochar application on the growth, yield, physiology, and WUE of different vegetable crops under DI regimes to determine the potential of biochar and DI used in combination to sustain vegetable productivity in water-limited areas. A review of 134 DI reports of vegetable crops revealed significant reductions in yield under all DI levels in 52% of cases and yields statistically similar to those of full irrigation [100% ETc (crop evapotranspiration) in most cases] under small water deficits in 44% of cases, thereby raising concerns about the sustainability of vegetable production under DI. The addition of biochar under DI has helped to compensate for yield losses of vegetables and further enhanced WUE. However, field studies investigating long-term soil-biochar interactions that strongly conclude the impact of biochar under moisture-stress conditions are lacking. The extent of water stress effects on varies with crop species, genotype, soil characteristics, and climatic conditions. In Chapter 2, we evaluated the effect of DI on eight vegetables to provide a quantitative estimate of yield and water productivity (WP) responses under variable soil textures, climates, and production systems (open-field and greenhouse). This meta-analyses study analyzed 425 yield and 388 WP comparisons of different DI levels to full irrigation (FI), extracted from 185 published studies representing 30 countries. Moving from the highest (>80%FI) to the lowest (<35%FI) irrigation level, the overall yield decline was 6.9 to 51.1% compared to FI, respectively. The WP gains ranged from 8.1 to 30.1%, with 35-50%FI recording the highest benefits. Soil texture affected the yield significantly only under the least irrigation class (<35%FI), wherein sandy clay and loam recorded the highest (82.1%) and the lowest (26.9%) yield decline, respectively. Among the climates, the temperate climate was overall the most advantageous with the least yield penalty (21.9%) and the highest WP gain (21.78%) across various DI levels. The DI application under the greenhouse caused lesser yield reduction compared to the open field. The WP gains due to DI were also higher for the greenhouse (18.4%) than open-field (13.6%). Consideration of yield penalties and the cost of saved irrigation water is crucial while devising the reduced irrigation amounts to the crops. The yield reductions under low to moderate water deficits (>65%FI) accompanied by gains in WP may be justifiable in the light of anticipated water restrictions. Chapter 3: Texas High Plains of the US is water-stressed like many arid and semi-arid regions of the world. A two-year (2019 and 2020) open-field study evaluated the effect of two types of biochar amendments (hardwood and softwood) and three irrigation rates [100%, 70%, 40% crop evapotranspiration (ETc) replacement] on physiology, plant growth, and yield of sweet corn in semi-arid West Texas. The chlorophyll content (ChlSPAD) in 40% ETc dropped significantly compared to 100% ETc and 70% ETc during the reproductive phase. Although water stress under 40% ETc decreased photosynthesis (Pn) to limit transpiration (E) by stomatal closure, it improved intrinsic water use efficiency (iWUE). The above-mentioned gas exchange parameters were comparable between 100% ETc and 70% ETc. Both biochar treatments increased ChlSPAD content over non-amended plots, however, their effect on gas exchange parameters was non-significant. All growth and yield-related parameters were comparable between 100% ETc and 70% ETc, but significantly greater than 40% ETc, except water productivity (WP). Both deficit irrigation treatments improved WP over full irrigation in 2019, but in 2020 WP gains were observed only under 70% ETc. Hardwood biochar decreased soil bulk density and increased soil porosity, but it had a marginal effect on water retention characteristics. These results suggest that 70% ETc can be used as an alternative to full irrigation to save water with a minimal yield penalty for sweet corn production in the West Texas region. Hardwood biochar application improved the vegetative biomass significantly but yield marginally during the first two years of application. A long-term study is required to test the effect of biochar under deficit irrigation beyond two years. Chapter 4: Root modifications can play a vital role in crop adjustments to soil water deficit. It is important to understand root growth and soil water depletion patterns to develop effective cropping systems, especially in semi-arid regions like Texas High Plains (THP). This study evaluated root growth, soil water depletion, and water use efficiency (WUE) of sweet corn under three deficit irrigation treatments [100%, 70%, and 40% crop evapotranspiration (ETc)] and biochar application (hardwood and softwood). The results revealed no interaction between irrigation and biochar treatments for almost all measured parameters. The 70% ETc treatment increased the root length density (RLD) over 100% ETc during 2019, while no differences were observed among irrigation treatments in 2020. Both deficit irrigations (70% and 40% ETc) increased soil water depletion compared to 100% ETc, the highest being in 40% ETc. The 70% ETc maintained a similar yield and increased WUE by 21% compared to 100% ETc across two years. However, 40% ETc resulted in a significant decline in yield and WUE in 2020. The hardwood biochar increased RLD over no biochar treatment without affecting the soil water status and WUE. Long-term studies are needed to investigate biochar effects beyond two years of application. In case of limited water availability, 70% ETc can be recommended as an alternative to 100% ETc in the THP of the US. Chapter 5: Soil amendment using biochar has been suggested as a strategy to improve long-term productivity by increasing nutrient availability, stimulating microbial activity, and improving soil water retention. Studying how biochar addition changes soil properties can also help us understand the underlying mechanisms by which it affects plant growth or productivity. This study evaluated the effect of two types of biochar (hardwood and softwood) on soil carbon (C), nitrogen (N), micronutrients, microbial abundance, and community structure under deficit irrigation rates [100%, 70%, 40% crop evapotranspiration (ETc) replacement]. Hardwood biochar increased total C by 14% in 2019 and 127% in 2020. In 2019, biochar had no effect on total N while hardwood biochar increased total N by 13% in 2020. Softwood biochar did not affect total C or total N. Inorganic nitrogen remained unaffected by biochar treatments. Biochar treatments had no effect on soil micronutrients. Differences in micronutrients among irrigation treatments can be due to differential uptake. Biochar could not alter the microbial abundance and community structure during the first year of application. However, water deficit under 40% ETc treatment increased the abundance of Gram-positive, Gram-negative, and Actinobacteria. Analyses of 2020 FAMEs data may help understand the abrupt change in total C under hardwood biochar treatment 2020. Long-term studies are required to test the longevity of biochar effect of soil beyond 2 years.


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Keywords
Water holding capacity, Water scarcity, Water depletion, Root distribution, Evapotranspiration, Water productivity, Crop physiology, Photosynthesis
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