Abstract Response of soil respiration (CO 2 emission) to simulated nitrogen (N) deposition in a mature tropical forest in southern China was studied from October 2005 to September 2006. The objective was to test the hypothesis that N addition would reduce soil respiration in N saturated tropical forests. Static chamber and gas chromatography techniques were used to quantify the soil respiration, following four‐levels of N treatments (Control, no N addition; Low‐N, 5 g N m −2 yr −1 ; Medium‐N, 10 g N m −2 yr −1 ; and High‐N, 15 g N m −2 yr −1 experimental inputs), which had been applied for 26 months before and continued throughout the respiration measurement period. Results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates found in the warm and wet growing season (April–September) and the lowest rates in the dry dormant season (December–February). Soil respiration rates showed a significant positive exponential relationship with soil temperature, whereas soil moisture only affect soil respiration at dry conditions in the dormant season. Annual accumulative soil respiration was 601±30 g CO 2 ‐C m −2 yr −1 in the Controls. Annual mean soil respiration rate in the Control, Low‐N and Medium‐N treatments (69±3, 72±3 and 63±1 mg CO 2 ‐C m −2 h −1 , respectively) did not differ significantly, whereas it was 14% lower in the High‐N treatment (58±3 mg CO 2 ‐C m −2 h −1 ) compared with the Control treatment, also the temperature sensitivity of respiration, Q 10 was reduced from 2.6 in the Control with 2.2 in the High‐N treatment. The decrease in soil respiration occurred in the warm and wet growing season and were correlated with a decrease in soil microbial activities and in fine root biomass in the N‐treated plots. Our results suggest that response of soil respiration to atmospheric N deposition in tropical forests is a decline, but it may vary depending on the rate of N deposition.
Abstract In order to validate whether optimizing irrigation and fertilization can improve degraded saline soil and increase wheat production, a 4‐year wheat field experiment on saline soil in the Yellow River Delta of China was conducted from October 2013 to June 2017. Eight optimizing treatments including two irrigation applcations of 90 (I90) and 135 (I135) mm/time, four irrigation times: at pre‐sowing, wintering, jointing, filling stages, and two fertilizer rates 225 kg N hm −2 ‐75 P 2 O 5 hm −2 ‐150 K 2 O hm −2 (F312), 225 kg N hm −2 ‐150 P 2 O 5 hm −2 ‐75 K 2 O hm −2 (F321) with two basal/topdressing ratios 1:1 (A11) and 1:2 (A12) were designed compared with no‐irrigation and fertilization (CK) and farmer mode (CM). The optimizing treatment combined I135 with F321 and A12 was the optimal practice for wheat production on degraded saline soil in this region. This treatment significantly decreased topsoil salinity on average by 21.97%, increased wheat grain yield, topsoil total N, available P and K, respectively, by an average of 0.74‐, 0.75‐, 1.13‐ and 0.78‐times, improved water utilization efficiency, water productive efficiency, nitrogen utilization efficiency, phosphorus utilization efficiency, respectively, by average of 1.26‐, 8.13‐, 0.32‐, 0.43‐times compared with the CM. These results demonstrate that the optimization of irrigation and fertilization can be extensively applied as a feasible and effective strategy to improve degraded saline soil, maintain soil nutrients, maximize crop yield, and enhance efficiency in other similar degraded saline soil areas of the world.
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