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Biochar is a carbon-rich product obtained by biomass pyrolysis and is considered as a means of carbon sequestration. However, there is limited knowledge regarding responses of soil respiration and C-cycle enzyme activities to BC in a calcareous soil. In this study, different biochar AS, TS, PP, CS were applied to the soil at different rates (0.5, 1.0, and 1.5%) The highest increase in soil organic C content was observed in the TS treatment, while the AS treatment caused a slight increase of soil organic C. The highest MBC content was recorded in AS treatment and the lowest was observed in TS. The highest CO2-C emission was recorded in the TS treatment. In contrast, the lowest CO2-C emission was observed in the PP treatment due to its high recalcitrant C content and was attributed to a positive priming effect, stabilizing BC mineralization to improve the soil. The highest β-galactosidase enzyme activity was observed in the CS treatment and the lowest activity was observed in AS. The highest change in β-glycosidase enzyme activity was observed of PP treatment and the lowest was in AS biochar application. Thus, TS treatment is recommended to increase the organic C content of soils, and the PP biochar can be used to reduce CO2-C emission. The TS, PP, and CS can be applied to increase enzyme activities. The study clearly shows that the addition of BC to arid soils may have a high potential to improve soil enzyme activities and subsequent carbon sequestration and biochemical cycles. [ABSTRACT FROM AUTHOR]

Soil phosphorus (P) loss risk and environmental impact can be assessed by different soil test indicators such as soil P storage capacity (SPSC), a site-specific and reliable measurement of soil P status. In this study, the changing trends of soil P saturation ratio (PSR) and SPSC in red soil (equivalent to Ultisol) were discussed after 10 consecutive additions of P solution with 20 mg P L−1, and the relationships between Olsen-P, CaCl2-P, and PSR, SPSC also were evaluated. Results showed that the soil PSR was increased to 0.22 at the end of P addition, and the accumulated P was high to 1625 mg kg−1. The threshold PSR of the red soil was determined to be 0.10, and the SPSC significantly decreased from 242.0 mg kg−1 to −382.1 mg kg−1 with the increase of P addition times. When SPSC = 0, the accumulated P in red soil was 487.7 mg kg−1. Therefore, there existed four stages for the soil P management in red soil according to the changes of SPSC and Olsen-P: short supply stage of soil P (SPSC>88 mg kg−1 and Olsen-P ≤ 20 mg kg−1), stable supply stage of soil P (68 mg kg−1< SPSC≤88 mg kg−1 and 20 mg kg−1< Olsen-P ≤ 40 mg kg−1); over supply stage of soil P (0< SPSC≤68 mg kg−1 and 40 mg kg−1< Olsen-P ≤ 108 mg kg−1), and the high loss risk stage of soil P (SPSC≤0 and Olsen-P > 108 mg kg−1). In the last stage, P fertilization must be stopped and environmental protection measures must be taken immediately. [ABSTRACT FROM AUTHOR]

Information on the effects of phosphorus (P) and sulfur (S) applications on crop response and soil-P status of two-row malt barley (Hordeum vulgare L.) under high-input conditions are limited in alkaline soils despite widespread fertilizer-P and -S use. A field study was conducted during the 2015 and 2016 growing seasons where the barley cultivars (ABI-Voyager and Moravian 69) were grown at five rates of P (0, 37, 73, 110, and 147 kg P ha−1) and three rates of S (0, 112, 224 kg S ha−1). ABI-Voyager had significantly greater biological yield (17,023 kg ha−1) and grain yield (7433 kg ha−1) but a lower (44%) harvest index (HI) than Moravian 69 (15,037 kg ha−1, 7168 kg ha−1 and 49%, respectively). Grain yield increased with rate of P-application until 37 kg P ha−1 where the maximum calculated yield was obtained at 98 kg P ha−1 by a quadratic model. Sulfur application had no significant effect on any of the measured crop or soil parameters. Olsen P increased linearly with greater fertilizer-P applications, indicating grain-P removal was not sufficient to reduce or retain STP concentrations at initial levels when P was applied. Crop-P uptake and soil-P response to fertilizer P applications are important, as remaining soil P is available for subsequent crop usage and may have potential negative environmental impacts. Thus, cultivar selection and appropriate fertilizer-P and S management will ensure optimal agronomic and economic returns while minimizing potentially negative environmental impacts for two-row malt barley produced in the western United States. [ABSTRACT FROM AUTHOR]