Search

The phosphorus (P) forms in long‐term fertilization determine the fate and transport of P in soil. However, the fate of various pools of organic P of added P in the long‐term measured with sequential chemical fractionation is not well‐understood. Four soil physical aggregates (>250, 125–250, 63–125 and <63 μm) from 0‐ to 20‐cm depth after 35 years of long‐term fertilization treatments including control (CK), nitrogen and phosphorus fertilizer (NP) and NP combined with farmyard manure (NPM) under continuous winter wheat were separated using settling tube apparatus. Results showed that the application of long‐term P fertilization had no apparent effects on promoting the mass proportion of soil aggregates except for >250 μm, where the NP and NPM treatments significantly increased the mass proportion by 60% and 70% over CK, respectively. Compared with CK, P fertilizer (NP and NPM) treatments significantly increased organic P (Po) contents in each size aggregate. In particular, mean labile Po increased by 35% and 246%, moderately labile Po by 125% and 161%, nonlabile Po by 105% and 170% and total Po (TPo) by 101% and 178%, respectively, under NP and NPM treatments, respectively. There was a significant correlation between soil organic carbon (SOC) and Po fractions. SOC was exponentially positively correlated with labile Po but linearly positively correlated with moderately labile Po, nonlabile Po and TPo fractions among soil aggregates. A reduced C:Po ratio (<100) in soil aggregates among treatment indicates a large amount of available P accumulated in soils, and soil P loss risk in the study site is still high. Our results show that the Po pool measured by sequential chemical fractionation may represent an important, yet often overlooked, source of P in agriculture ecosystems. According to the result, long‐term mineral P fertilizer combined with organic amendments better sustains soil structural stability in large aggregates, contributing more Po availability in the moderately labile P followed by labile P in soil aggregates. [ABSTRACT FROM AUTHOR]

A 2-year field study was conducted to measure nitrous oxide (N2O) and methane (CH4) in a rain-fed spring maize cropland in the Loess Plateau, P. R. China, and to determine the effects of optimized nitrogen (N) fertilization practices on urea-derived N2O emission factor (EF), grain yield, net greenhouse gas (NGHG) emission, and net greenhouse gas intensity (NGHGI). Five treatments were considered, including control (CK), conventional N fertilization (Con), optimal N fertilization (Opt), optimal N fertilization plus nitrification inhibitor (Opt + DCD), and optimal N fertilization with slow release urea (Opt + SR). Soil acted as a small sink for atmospheric CH4. Nitrogen fertilization and heavy rainfall events (>40 mm) were the main factors controlling N2O emissions. The annual mean EF ranged from 0.12 to 0.55%. Compared to conventional N fertilizer, nitrification inhibitor decreased the annual cumulative N2O, NGHG, and NGHGI emissions by 45, 52, and 48%, respectively, without decreasing grain yield. In conclusion, nitrification inhibitor addition was the most effective practice to reduce N2O emissions in the rain-fed regions of Loess Plateau. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilization has a considerable effect on food production and carbon cycling in agro-ecosystems. However, the impacts of N fertilization rates on the temperature sensitivity of soil respiration (Q10) were controversial. Five N rates (N0, N45, N90, N135, and N180) were applied to a continuous winter wheat (Triticum aestivum L.) crop on the semi-arid Loess Plateau, and the in situ soil respiration was monitored during five consecutive years from 2008 to 2013. During the growing season, the mean soil respiration rates increased with increasing N fertilization rates, peaking at 1.53 μmol m−2s−1 in the N135 treatment. A similar dynamic pattern was observed during the non-growing season, yet on average with 7.3% greater soil respiration rates than the growing season. In general for all the N fertilization treatments, the mean Q10 value during the non-growing season was significantly greater than that during the growing season. As N fertilization rates increased, the Q10 values did not change significantly in the growing season but significantly decreased in the non-growing season. Overall, N fertilization markedly influenced soil respirations and Q10 values, in particular posing distinct effects on the Q10 values between the growing and non-growing seasons. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen (N) and precipitation are the main limiting factors in food production under rain-fed cropping systems in arid and semiarid regions. A long-term field experiment was conducted from 1984 to 2009 in the Changwu State Key Agro-Ecological Experimental Station of the Loess Plateau, China, to study interactions between precipitation and N fertilization. Winter wheat (Triticum aestivum L.) was grown with N fertilization at 0, 45, 90, 135, and 180kgNha−1. With 25-year N fertilization, soil organic carbon and total N were increased by 18% and 26%, respectively. Mean yields and precipitation use efficiency (PUE) levels with N fertilization were increased by onefold to twofold compared with unfertilized soils. Generally, during the period of 1984–2009, grain yields with 45–`180kgN ha−1 increased at the rate of 38–49kgha−1 year−1 (p <0.05), whereas PUE increased at the rate of 0.071–0.088kgmm−1 year−1. These increases over time are largely attributable to improvements in soil organic carbon and total N. Variations in yield were proportionally reduced by N fertilization, but heavily depended on the fluctuation of precipitation. Grain yields with 45–180kgN ha−1 decreased by approximately 10%–45% (p <0.05) in the dry years (drought index<−0.35) compared with the normal years, whereas significant increases were not detected in the wet years (drought index>0.35). Grain yields with 90–180kgN ha−1 were positively correlated (p <0.05) with fallow season precipitation, but insignificantly correlated with growing season precipitation. The optimum N fertilization rates in the dry, normal and wet years increased following an increasing sequence of 45, 135 and 180kgNha−1. These results have significant implications for optimizing N fertilization and maximizing yield and PUE in rain-fed cropping systems in arid and semiarid regions. [Copyright &y& Elsevier]

Aims: Concerns over food security and global climate change require an improved understanding of how to achieve optimal crop yields whilst minimizing net greenhouse gas emissions from agriculture. In the semi-arid Loess Plateau region of China, as elsewhere, fertilizer nitrogen (N) inputs are necessary to increase yields and improve local food security. Methods: In a dryland annual cropping system, we evaluated the effects of N fertilizers on crop yield, its long-term impact on soil organic carbon (SOC) concentrations and stock sizes, and the distribution of carbon (C) within various aggregate-size fractions. A current version (RothC) of the Rothamsted model for the turnover of organic C in soil was used to simulate changes in SOC. Five N application rates [0 (N0), 45 (N45), 90 (N90), 135 (N135), and 180 (N180) kg N ha] were applied to plots for 25 years (1984-2009) on a loam soil (Cumulic Haplustoll) at the Changwu State Key Agro-Ecological Experimental Station, Shaanxi, China. Results: Crop yield varied with year, but increased over time in the fertilized plots. Average annual grain yields were 1.15, 2.46, 3.11, 3.49, and 3.55 Mg ha with the increasing N application rates, respectively. Long-term N fertilizer application increased significantly ( P = 0.041) SOC concentrations and stocks in the 0-20 cm horizon. Each kilogram of fertilizer N applied increased SOC by 0.51 kg in the top soil from 1984 to 2009. Using RothC, the calculated annual inputs of plant C (in roots, stubble, root exudates, etc.) to the soil were 0.61, 0.74, 0.78, 0.86, and 0.97 Mg C ha year in N0, N45, N90, N135 and N180 treatments, respectively. The modeled turnover time of SOC (excluding inert organic C) in the continuous wheat cropping system was 26 years. The SOC accumulation rate was calculated to be 40.0, 48.0, 68.0, and 100.0 kg C ha year for the N45, N90, N135 and N180 treatments over 25 years, respectively. As aboveground biomass was removed, the increases in SOC stocks with higher N application are attributed to increased inputs of root biomass and root exudates. Increasing N application rates significantly improved C concentrations in the macroaggregate fractions (>1 mm). Conclusions: Applying N fertilizer is a sustainable practice, especially in carbon sequestration and crop productivity, for the semiarid Loess Plateau region. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilization has been repeatedly reported to strongly influence soil properties and crop growth. However, there is little information about the combined effects of soils and crops on soil CO 2 fluxes under N fertilization. In this study, in situ soil respiration, soil physicochemical properties, microbial communities and crop properties were measured for eight years (2008 to 2016) on the Loess Plateau. Five rates of N fertilization were applied to different plots to compare the soil respiration rate and its temperature sensitivity (Q 10). Nitrogen fertilization significantly increased mean annual cumulative soil respiration (R cum) by 25%–44%. R cum had a positive correlation with grain yield, and the carbon emission efficiency (grain yield produced per unit of carbon emission) under N-fertilized plots was 1.62–2.52 times that of unfertilized plots. R cum also had a positive correlation with root biomass and the root N concentration but showed a negative correlation with the root C/N ratio. The Q 10 values under N-fertilized plots decreased by half at a diurnal scale, but had a smaller reduction (i.e. , 0.04–0.09) at an annual scale compared to unfertilized plots. The decreased Q 10 values under N-fertilized plots also resulted from the lower aromaticity of dissolved carbon (SUVA 254) (7.40 vs. 10.53 L mg C−1 m−1). In addition, the altered R cum and Q 10 values were affected by the varied bacteria community derived from N fertilization, which was related to Acidobacteria , Chloroflexi , Proteobacteria and Bacteroidetes. Therefore, N fertilizer applications regulate the combined effects of soil and crop parameters on soil respiration and the Q 10 value. This study suggests that, due to the lower carbon emission efficiency and higher SOC concentration under N-fertilized plots, N fertilizer applications may be used to sustain crop yields and increasing SOC storage while minimizing carbon emission impacts to the environment on the Loess Plateau. • Nitrogen fertilizer application increased soil respiration rate (SR) but decreased Q 10. • Variation in SR and Q 10 was resulted from altered photosynthetic rate, C/N, SUVA 254 , and bacteria community. • Nitrogen fertilizer application increased carbon emission efficiency. [ABSTRACT FROM AUTHOR]

Temperature sensitivity of soil respiration ( Q 10 ) is an important parameter when modeling the effects of global warming on terrestrial ecosystem carbon release. Widely applied chemical fertilizers can significantly affect soil productivity and carbon cycling in agroecosystems. However, little is known about how Q 10 responds to chemical fertilization under different levels of initial soil fertility. On the Chinese Loess Plateau, changes in soil respiration rates and Q 10 were investigated in soils of two fertility levels: low fertility (L) and high fertility (H). For each soil fertility level, there was one control plot and one chemical fertilized plot (+NP), which in total formed four treatments: L, L + NP, H and H + NP. All the treatments were replicated for three times on a continuous winter wheat cropping system. Respiration rates of surface soil in each treatment were in situ monitored from October 2010 through September 2015. Our results showed that after NP fertilization, soil respiration rates were increased by 46% in low fertility soil, yet only by 14% in high fertility soil ( P  < 0.05). The Q 10 after NP fertilization was significantly decreased by 6.9% in low fertility soil, but was unchanged in the high fertility soil. The Q 10 variation might be attributed to the different response of microbial respiration Q 10 in the two soils. The decreased Q 10 with NP fertilization in the low fertility soil was possibly due to N-induced increase of substrate quality for soil microbes and increased activities of both cellobiohydrolase and polyphenol oxidase. In the high fertility soil, the unchanged Q 10 with NP fertilization may be the integrated result of less affected substrate quality and neutral response of polyphenol oxidase activity. Overall, our results suggested that the effects of NP fertilization on soil respiration and its temperature sensitivity varied with soil initial fertility levels, and therefore must be properly accounted for when estimating potential effects of local agricultural management to regional agroecosystems under future climate conditions. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) fertilization has the potential to alter soil respiration temperature sensitivity ( Q 10 ) by changing soil biochemical and crop physiological process. A four-year field experiment was conducted to determine how Q 10 responded to these biochemical and physiological changes in rain-fed agro-ecosystems on the semi-arid Loess Plateau. Soil respiration, as well as biotic and abiotic factors were measured in winter wheat ( Triticum aestivum L.), with three fertilization treatments: (no fertilization (CK), 160 kg N hm − 1 (N), and 160 kg N ha − 1 with 39 kg P ha − 1 (N + P). Mean annual soil respiration rate (calculated by averaging the four years) in the N treatment and N + P treatment was 18% and 48% higher than that in the CK treatment, respectively; and it was increased by 26% (14%–48%) in the N + P treatment as compared with that in the N treatment. The decrease of Q 10 in the N and N + P treatments against the CK treatment was not stable for each year, ranging from 0.01 to 0.28. The maximum decrease of Q 10 in the N and N + P treatments was 10% and 15% in 2014–2015, while in other years the decrease of Q 10 was numerical but not significant. Soil microbial biomass carbon (SMBC) was increased by 10% and 50%, dissolved organic carbon (DOC) was increased by 6% and 21%, and photosynthesis rate was increased ranging from 6% to 33% with N and N + P fertilization. The relative abundance of Acidobacteria, Actinobacteria and Chloroflexi were significantly higher by 32.9%–54.1% in N addition soils (N and N + P) compared to CK treatment, whereas additional P application into soils increased the relative abundance of the family Micrococcaceae, Nocardioidaceae and Chitinophagaceae. Soil respiration was positively related to SMBC, DOC and photosynthesis rate ( p < 0.05). However, variation in Q 10 may be related to the increase of soil mineral N content and variation of the relative abundance of soil microbial community in our study. Nitrogen and additional phosphorus fertilization regimes affect soil respiration and temperature sensitivity differently. [ABSTRACT FROM AUTHOR]

Temperature sensitivity of soil respiration ( Q 10 ) is an important mechanism for the possible feedback between global carbon cycle and climate system. Knowledge of how crop types and nitrogen (N) fertilization affect Q 10 is critical for estimating soil respiration and carbon cycling in agro-ecosystem. A two-year field experiment was conducted with cold-resistant (winter wheat; Triticum aestivum L.) and thermophilic (spring maize; Zea mays L.) crops at two N fertilization levels (no fertilization (CK) and 160 kg N hm −1 ) from October 2013 to September 2015 in semi-arid Loess Plateau. Annual mean soil respiration and Q 10 in maize were 20% (1.85 vs. 1.54 μmol m −2 s −1 ) and 36% (2.49 vs . 1.83) higher than that in wheat. Nitrogen fertilization resulted in a 35% increase in annual mean soil respiration (1.95 vs. 1.44 μmol m −2 s −1 ) and a 11% decrease in Q 10 (2.05 vs . 2.28) compared with the CK treatment. Soil respiration was positively related to root biomass, whereas no significant relationship was found between root biomass and Q 10 . Therefore, it can be concluded that soil respiration and temperature sensitivity of soil respiration are significantly influenced by crop types and N fertilization regimes, which should be considered in calculating carbon budget in agro-ecosystem using carbon models. [ABSTRACT FROM AUTHOR]