[Characteristics and influencing factors of soil nitrification potential in coastal salinized farmland]. / æ»¨æµ·ç›æ¸å†œç”°åœŸå£¤ç¡åŒ–åŠ¿ç‰¹å¾åŠå ¶å½±å“å› ç´ .

Understanding the nitrification capacity of coastal saline farmland soils and its main drivers is of great significance to regulate soil nitrification and improve the utilization efficiency of nitrogen fertilization in farmland. Using a combination of field investigations and laboratory analyses, we examined farmland soil nitrification potential and soil physical, chemical, and biological properties in the coastal muddy tidal flat saline soil area (Dongying and Dongtai). We established the correlation between soil properties and soil nitrification potential with multiple stepwise regression analyses and structural equation modeling (SEM). The results showed that soil pH value was relatively stable and other soil properties and soil nitrification potential varied in coastal saline farmland. The soil nitrification potential ranged from 0.04 to 10.42 mg·kg-1·d-1 and decreased with the increases of soil salinization level. Soil nitrification potential had the strongest correlation with soil organic matter, cation exchange capacity, and Cl-, with the correlation coefficient being 0.409, 0.397 and -0.337, respectively. The results of multiple stepwise regression analysis showed that Na+, silt, cation exchange capacity, and CO32-+HCO3- were the main influencing factors of soil nitrification potential. The results from the SEM analysis suggested that Na+, silt, cation exchange capacity, and CO32-+HCO3- directly affected soil nitrification potential, and soil organic matter, clay, Cl- and SO42- had indirect effects. In all, soil Na+ and cation exchange capacity were the two main factors affecting nitrification. Adjusting soil NaCl content and cation exchange capacity was an effective means of regulating soil nitrification.

Biochar Addition Inhibits Nitrification by Shifting Community Structure of Ammonia-Oxidizing Microorganisms in Salt-Affected Irrigation-Silting Soil.

Biochar has been widely recognized as an effective and eco-friendly ameliorant for saline soils, but information about the mechanism of how biochar influences nitrification in salt-affected agroecosystem remains fragmented. An incubation experiment was performed on the salt-affected soil collected from a three-consecutive-year experiment at biochar application gradients of 7.5 t⋅ha-1, 15 t⋅ha-1 and 30⋅t ha-1 and under nitrogen (N) fertilization. Responses of the nitrification rate (NR), numbers of ammonia monooxygenase (amoA) gene copies, and community structures of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to biochar application were investigated. The results indicated that, under N fertilization, the NR and numbers of amoA-AOB and amoA-AOA gene copies negatively responded to biochar addition. Biochar application increased the community diversity of AOB but decreased that of AOA. Biochar addition and N fertilization shifted the AOB community from Nitrosospira-dominated to Nitrosospira and Nitrosomonas-dominated, and altered the AOA community from Nitrososphaera-dominated to Nitrososphaera and Nitrosopumilus-dominated. The relative abundance of Nitrosospira, Nitrosomonas and Nitrosopumilus decreased, and that of Nitrosovibrio and Nitrososphaera increased with biochar application rate. Soil SOC, pH and NO3--N explained 87.1% of the variation in the AOB community, and 78.1% of the variation in the AOA community was explanatory by soil pH and SOC. The SOC and NO3--N influenced NR through Nitrosovibrio, Nitrosomonas, Norank_c_environmental_samples_p_Crenarchaeota and amoA-AOB and amoA-AOA gene abundance. Therefore, biochar addition inhibited nitrification in salt-affected irrigation-silting soil by shifting the community structures of AOB and AOA and reducing the relative abundance of dominant functional ammonia-oxidizers, such as Nitrosospira, Nitrosomonas and Nitrosopumilus.

[Influencing mechanism of soil salinization on nitrogen transformation processes and efficiency improving methods for high efficient utilization of nitrogen in salinized farmland]. / ç›æ¸åŒ–å¯¹å†œç”°æ°®ç´ è½¬åŒ–è¿‡ç¨‹çš„å½±å“æœºåˆ¶å’Œå¢žæ•ˆè°ƒæŽ§é€”å¾„.

Based upon the review of the status of nitrogen use efficiency in salinized farmland in China, we summarized the effect of salinization on key processes of nitrogen transformation in farmland soil, analyzed the microbial mechanism underlying nitrogen transformation, and summed up the main ways for high efficient utilization of nitrogen in salinized farmland. Salinization had thre-shold effects on mineralization, nitrification, and denitrification of nitrogen from farmland soil, with the influence varying greatly in different scopes. Salinity and secondary barriers had different effects on microorganisms, with threshold in their effects. The most widely used methods for nitrogen synergism regulation in salinized farmland include soil conditioner, biomass material, growing salt-tole-rant plants, optimizing the ratio of different nitrogen forms, and biological inhibitor. We proposed current research shortcomings and future research directions of nitrogen cycle processes in salinized farmland. This study was of great significance for reducing nitrogen loss, enhancing utilization of nutrient from fertilizers, and controlling agricultural non-point source pollution in salinized farmland.

Biochar and fulvic acid amendments mitigate negative effects of coastal saline soil and improve crop yields in a three year field trial.

China with large area of land planted with crops are suffering secondary salinization in coastal area for the lack of fresh water and saltwater intrusion to the groundwater. The purpose of this study was to investigate the effects of biochar (BC) and fulvic acid (FA) on the amelioration of coastal saline soil and their impact on crop yields under maize-barley rotation system. A three year field experiment was conducted in a saline soil on a farm in coastal area of east Jiangsu Province, China. A maize-barley rotation system had been carried out for ten years with local conventional management before the experiment. The saline soil was amended with BC at rates of 0, 7.5 t ha-1 (BC1), 15 t ha-1 (BC2) and 30 t ha-1 (BC3) alone or combined with fulvic acid (1.5 t ha-1) compared with control. Fertilizers were applied under normal planting strategies. The BC was added only once during the four growing seasons, and the FA was applied before each sowing. Soil salinity changed significantly during the three year field experiment. This was mainly due to the great quantity of rain during the period of maize cultivation. Although Na+, Cl- and SO42- in BC and /or FA treatments significantly decreased, the pH value increased up to 9.0 as the CO32- + HCO3-content increased. Total organic carbon (TOC) and phosphorus (TP) responded positively to biochar addition rate. BC applied with appropriate rate at 15 t ha-1 (BC2) in combination with FA showed optimal effects on soil salinity amelioration, soil physics properties regulation, soil nutrition improvement and crop yields increase. The TOC and TP was 5.2 g kg-1 and 507 mg kg-1 in BC2 + FA treatment, which were lower than BC3 and BC3 + FA treatments. However, the highest total grain yield was obtained in the BC2 + FA treatment, and the total yield was increased by 62.9% over the CK. This study emphasizes that using combined organic amendment of BC with FA for profitable and sustainable use of salt-affected soils would be practicable.

[Characteristics of soil salinity profiles and their electromagnetic response under various vegetation types in coastal saline area].

Aiming at the intrinsic relationships between vegetation type and soil salinity in coastal saline area, and by using electromagnetic induction EM38 and field sampling method, the characteristics of soil salinity profiles under various vegetation types in typical coastal saline region of the Yellow River Delta were analyzed, and the electromagnetic response characters of the salinity profiles were compared. The results showed that across the study area, soil salinity exhibited the characteristics of top enrichment and strong spatial variation. The horizontal electromagnetic conductivity EM(h) responded well to soil salinity at upper layers, and the response of vertical electromagnetic conductivity EM(v) to soil salinity at deeper layers was superior to that of EM(h). Soil salinity profiles were classified into inverted, normal, and uniform types. The vegetation types of inverted salinity profiles were mainly bare land and Suaeda salsa, while those of normal and uniform salinity profiles were cotton and weed, respectively. The sequence of top enrichment intensity was bare land > S. salsa land > weed land > cotton land. With the change of vegetation type of cotton-weed-S. salsa-bare land, the EM(v)/EM(h) value of salinity profiles decreased gradually. Nonparametric test results showed that there was a significant correlation between vegetation type and electromagnetic response characters, and the distribution characters of EM(v)/EM(h) under various vegetation types varied significantly.