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Low soil aeration often causes hypoxia stress in the root zone, deteriorating the normal metabolic activities and growth of crops. Micro-nano oxygenation technology can be expected to serve as the potential type of irrigation water oxygenation. But it is still lacking in the oxygenation effect and the change of dissolved oxygen concentration after entering the soil. In this study, a series of indoor simulation experiments were carried out to clarify the effect of micro-nano oxygenated water addition on the dissolved oxygen dissipation in soil. Three kinds of oxygen concentration gradient water [CK: Tap water (8-9 mg/L), O1:15 mg/L, O2:20 mg/L] were prepared to supersaturate the soil moisture in the air-dried and pre-cultivated soil using the micro-nano oxygenation. The oxygen micro-electrode was used to monitor the changes in dissolved oxygen concentration in the soil in real-time. The experiment was also performed on the treatments with the glucose and ammonium sulfate as the carbon and nitrogen substrates in the irrigation water under the different dissolved oxygen content. The variation soil dissolved oxygen dissipation was then determined in each treatment. The results show that: 1) A two-stage law was found in the rapid decline stage, followed by the slow decline stage, according to the increase of soil dissolved oxygen concentration with time. The dissipation of soil-dissolved oxygen was dominated by gas diffusion in the rapid decline stage. The dissipation curve conformed to a logarithmic function. In the slow decline stage, the consumption of soil-dissolved oxygen was mainly microbial consumption, where the dissipation curve conformed to the Logistic or linear function. 2) In the rapid decline stage of the air-dried soil test, the higher the oxygen concentration was, the longer the high oxygen state in the soil was maintained, and the higher the dissolved oxygen consumption rate was, compared with the conventional water treatment. The retention time of dissolved oxygen in the O1 and O2 treatment was prolonged by 40.11%, and 189.62%, respectively, while, the maximum consumption rate of dissolved oxygen increased by 301.53%, and 545.8%, respectively. The rapid decline stage of the pre-cultured soil test also showed a similar law to the air-dried soil test. Compared with the conventional water treatment, the dissolved oxygen dissipation time of O1 and O2 treatment was prolonged by 445.16%, and 2 741.94%, respectively, whereas, the maximum consumption rate of dissolved oxygen increased by 643.78%.and 404.32%, respectively; 3) In the slow decline stage of the air-dried soil test, the maximum consumption rates of O1 and O2 increased by 80%, and 75%, respectively, compared with the conventional. In the slow decline stage of the pre-cultured soil experiment, the overall consumption rate of dissolved oxygen in the pre-cultured soil increased by 3-4 times, compared with the air-dried soil. It infers that the consumption time was shortened several times accordingly. The treatments of CK, O1, and O2 were all carried out the oxygen consumption at a constant rate of about 0.06 mg/(L·min-1). 4) On the whole, the substrate was the key limiting factor of dissolved oxygen consumption. Specifically, the dissolved oxygen consumption rate increased by 2-3 times, whereas the dissipation time shortened by 2-3 times. In summary, there was a rapid and then slow decline stage in the change of soil dissolved oxygen content with time after the application of micro-nano oxygenated water. An overall downward trend with first fast and then slow can be expected to effectively enhance the oxygen concentration in the soil for a long period of time. The existence time of available oxygen in the soil can provide a better oxygen environment in the crop roots and soil microorganisms. Keywords: soils; [ABSTRACT FROM AUTHOR]

Rice is the largest grain crop in China, and its unique flooded paddy soil provides necessary condition for the occurrence of denitrification.However, the problems of nitrogen utilization decline and greenhouse gas emissions caused by denitrification have gained increasing concern.As a biological process driven by microorganisms, denitrification is affected by many factors such as soil pH and organic carbon sources.To reveal the effect of exogenous organic carbon on the functional activity and potential of denitrifying microorganisms in paddy soils with different pH values, this study added glucose to two paddy soils with different initial pH values and analyzed the abundance of key functional genes（nirK/S,nosZ） for denitrification at DNA and RNA levels.The results showed that the glucose reduced soil pH,the degree of which rose with the increase of the glucose concentration.The added glucose also enhanced soil denitrification, which was observed only in alkaline paddy soil.The responses of number and expression of nirK and nirS genes to glucose addition were significantly different between the two soils with different pH values, and the response degree of nirK gene was relatively higher.In acidic paddy soil, the number and expression of nosZ gene decreased with the increase of carbon source concentration; while in alkaline paddy soil, low concentration glucose significantly stimulated the number and expression of nosZ gene, but high concentration glucose caused soil acidification, which then inhibited the number and expression of nosZ gene.This study shows that exogenous organic carbon source affects the function and activity of denitrifying microorganisms in paddy soil from aspects of carbon source supply and soil acidification, which in turn influences the occurrence of denitrification and subsequent nitrous oxide emission. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is one of the macroelements necessary for plant growth, second only to nitrogen (N) in importance. Most studies have shown that phosphorus is easily adsorbed by soil particles or forms insoluble precipitates with some substances in the soil (Fe, Al, and Ca), leading to the less biological availability of phosphorus. A large amount of phosphorus fertilizer is also applied to the soil for the needs of crops in practice. As such, the content of total phosphorus and Olsen-P in farmland soil has continued to rise in recent years in China. For instance, the average available phosphorus content in farmland soil was ranging from only 7.4 to 24.7 mg/kg from the 1980s to 2007. Excessive application of phosphorus fertilizer has posed a great threat to the physical and chemical properties of soil structure. This study aims to reveal the effect of phosphorus addition on the one-dimensional vertical infiltration characteristics of soil water. A series of soil infiltration experiments of adding phosphorus with water (CK, P1, P2, P3, P4) and cultivating soil infiltration experiments with phosphorus (ICK, IP1, IP2, IP3, IP4) were carried out. Five P gradients were set for each experiment, which were 0, 0.075, 0.15, 0.225, 0.3 g/kg. The results showed that: 1) Phosphorus application with water presented no significant effect on the soil infiltration during the infiltration process; 2) The water infiltration capacity was significantly enhanced after the soil was incubated with the phosphorus addition for 90 days. Compared with the control ICK, the cumulative infiltration amount of IP1, IP2, IP3, and IP4 increased by 7.82%, 8.85%, 9.82%, and 11.21%, respectively, whereas, the corresponding infiltration time decreased by 7.77%, 14.56%, 22.33%, and 27.18%, respectively. The cumulative infiltration amount and the migration speed of the wetting front increased significantly, with the increase of the phosphorus concentration. There was an excellent linear relationship between the infiltration parameters and phosphorus concentration in the fitted Kostiakov and the migration distance-time formula of the wetting front; 3) The IP3, and IP4 treatments presented a significantly larger amount of 0.25-2 mm particle size aggregates, compared with the control ICK without phosphorus. The amount increased by 35.9%, and 51.28%, respectively, indicating the addition of phosphorus significantly increased the proportion of large aggregates of 0.25-2 mm in the soil, thus changing the one-dimensional vertical infiltration characteristics of soil water. In summary, the duration of phosphorus addition in the soil was closely related to the change in soil structure. Phosphorus addition also increased the proportion of large aggregates of 0.25-2 mm in the soil, thereby enhancing the infiltration capacity of the soil. It is very necessary to consider the effect of phosphorus fertilizer on soil structure, especially in the case of excessive application of phosphorus fertilizer. Therefore, the phosphorus application can be combined with the soil infiltration capacity, in order to reveal the effect of phosphorus addition on the soil moisture and infiltration capacity. The finding can provide a theoretical basis for the rational and standardized phosphorus application. [ABSTRACT FROM AUTHOR]

Water shortage and excessive application of nitrogen fertilizer are two prominent problems in the agricultural production system globally. Finding new ways to improve the efficiency of water and nitrogen fertilizer use is of great significance to the realization of sustainable agricultural development. Oxygenated water is an efficient and non-pollution irrigation water treatment technology. The application of oxygenated water in the irrigation in agricultural production can improve the soil environmental conditions and promote crop growth. In this study, the objective was to investigate the effect of oxygenated water on soil nitrification under different water contents. The oxygenated water was produced by a rapid generation device of micro-nano bubbles, and the dissolved oxygen concentration in water was monitored to reach 20 mg/L. Silt sandy loam soil sampled from the Xinjiang cotton production area was incubated with ammonium sulfate as additional substrate under controlled conditions in the laboratory. Either ordinary water or oxygenated water was added into soil to obtain different soil moisture conditions (30%, 60%, 100% and 175% of Water Holding Capacity, WHC). During the incubation, soil samples were taken and NH4 +-N and NO3 --N contents were analyzed on day 0, 1, 2, 4, 6, 8, 12, 16 and 20. The nitrification kinetic equation and nitrification intensity were used to quantitatively evaluate the dynamic change characteristics of NH4 +-N and NO3 --N content over time. The initial consumption rate of NH4 +-N, the maximum consumption rate of NH4 +-N, the time to reach maximum consumption rate and the average production rate of NO3 --N from each treatment were analyzed and compared. The results showed that the nitrogen transformation of the studied silt sandy loam was dominated by nitrification. During incubation, the NH4 +-N added into soil was consumed, and almost depleted in all treatments except the ones with 30%WHC; The NO3 --N was produced simultaneously. For both the ordinary water and the oxygenated water treatments, with the increase of moisture content, the soil nitrification intensity first increased to the maximum at 100%WHC, and then decreased. Under different soil moisture conditions, oxygenated water treatment affected the soil nitrification intensity to varying degrees. Compared with ordinary water treatment, oxygenated water promoted nitrification most significantly under the condition of 60%WHC, the maximum consumption rate of soil NH4 +-N increased by 8.9%; the peak occurrence time was earlier, and the average generation rate of NO3 --N increased. Under the condition of 100%WHC, no significant difference was found in the consumption of NH4 +-N in the oxygenated water treatments, and only the average generation rate of NO3 --N increases by 1.58 times. Under the condition of 175%WHC, the maximum consumption rate of NH4 +-N in the soil decreased by 21.5% and the peak occurrence time lagged; and the average generation rate of NO3 --N did not change obviously. This research proposes the most suitable water condition for the promotion of soil nitrogen transformation by oxygenated water, which provides an important theoretical basis for the development of agricultural efficient water and fertilizer utilization technology. [ABSTRACT FROM AUTHOR]