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To understand the characteristics of ammonia volatilization in Losses Plateau, an experiment was conducted in a typical solar greenhouse involving four treatments. Intermittent ventilation chamber method was used to measure NH 3 volatilization over the period of tomato-watermelon rotation. The results showed that nitrogen transformation was rapid in solar greenhouse system. The peak NH 3 volatilization rate appeared one to two days after fertilization with the range from 0.26 to 2.02 kg N·hm -2 ·d -1 . The NH 3 volatilization lasted for about one week in all treatments. No significant differences were recorded in terms of cumulative NH 3 volatilization among all nitrogen fertilizer input treatments. The cumulative NH 3 losses further increased about 46.7% in two seasons under the same nitrogen application rate, however when irrigation application was decreased. The average NH 3 vola-tilization rate and cumulative NH 3 losses in watermelon season were higher compared to tomato season, which might be attributed to high temperature during watermelon season. Soil NH 4 + -N content, water filled pore space, soil temperature of 0-5 cm layer and air temperature all had extremely significant effect on NH 3 volatilization rate, while a negative correlation was observed between soil pH and NH 3 volatilization rate. Between the different cropping seasons, the rate of NH 3 losses were different, and decreased with decreases in nitrogen input, while reduced irrigation volume increased NH 3 volatilization under the same nitrogen application rate.3 volatilization under the same nitrogen application rate.

A long-term fertilizer experiment was conducted to determine the precise effects of nitrogen (N) fertilization on the yield and quality of cucumber, which were grown in greenhouse located in the coastal hilly region of East China. This work included four treatments with varying levels of chemical N application (N 1 , 800 kg·hm -2 , N 2 , 600 kg·hm -2 and N 3 , 400 kg·hm -2 , CK, no fertilization) plus ON (organic N 400 kg·hm -2 ). Results showed that a 50% reduction of N fertilization (N 3 ) produced no significant effects on yield, when compared with the local conventional practice (N 1 ). Importantly, fruit nitrate content for cucumbers with N fertilization ranged from 94.2 to 136.1 mg·kg -1 , which was acceptable according to the National Food Safety Standard of China. However, when compared with no fertilization control, N fertilization increased nitrate content by 18.1%-44.5%. Chemical N fertilization resulted in a decrease of vitamin C, soluble sugar and soluble protein contents in cucumber, and caused significant temporary changes of soil pH and other chemical and physical properties of the soil. No significant correlations were found between cucumber yields, economic benefit and soil property variables under the excessive use of N fertilizer. It was concluded that N fertilization could be reduced by half with no significant reduction of fruit yield and quality for cucumbers cultivated in greenhouse located in the coastal hilly region of East China.

Uptake of nitrogen (N) and phosphorus (P) and their purification capacity for five native submerged macrophytes were investigated in laboratory simulated hydrostatic conditions,including Hydrilla verticillata , Vallisneria natans , Ceratophyllum demersum , Myriophyllum spicatum , Potamogeton maackianus. The results indicated that the moisture contents of different submerged macrophytes were almost the same before and after the test,with the range of 89.8%-92.0%.The net accumulated biomass changed from 1.52 g·m -2 to 12.92 g·m -2 among different submerged macrophytes,and the highest net accumulated biomass of Hydrilla verticillata was 8.5 times higher than the lowest plant of Potamogeton maackianus .The N and P contents of five submerged macrophytes ranged from 26.54 to 34.44g·kg -1 and from 2.54 to 4.01g·kg -1 ,respectively,and the N and P contents of Ceratophyllum demersum were relatively high.Total N and P removal efficiency of different submerged macrophyte treatments had ranges of 63.8%-83.1% and 49.2%-70.8%,significantly higher than those of the CK treatment (39.9% and 36.9%),respectively,and the removal efficiency decreased in the order of Hydrilla verticillata > Ceratophyllum demersum > Vallisneria natans > Myriophyllum spicatum > Potamogeton maackianus .Total N and P removal efficiencies of different submerged macrophyte treatments were significantly correlated with net accumulated biomass,with correlation coefficients of 0.994( P <0.01) and 0.996( P <0.01).The contribution of direct N and P uptake to different submerged macrophytes had the ranges of 1.5%-13.3% and 2.2%-13.2%,and the synergism contribution (deducting self-purification capacity of water) of different submerged macrophytes ranged 22.5%-29.9% and 10.1%-20.6%,indicating that the synergistic effect of submerged macrophytes purification was much more significant than the direct uptake effect in the process of water purification.

Maize straws were collected from different treatments of two long-term fertilization studies, their carbon (C)/nitrogen (N) ratios were determined, and their C and N mineralization rates in soil were compared in an aerobic incubation test. The results showed that comparing with no fertilization, applying chemical fertilizers (NPK) or chemical fertilizers plus manure (MNPK) increased the N content and decreased the C/N ratio of maize straw. The amounts of mineralized and immobilized C and N of the straws from different fertilization treatments differed with incubation time. The straws from treatments NPK, MNPK, and N240 had significantly higher C mineralization rates than that from the treatment without fertilization. After incubation for 60 days, the straw from treatment NPK had the highest C mineralization rate (13.24% of added organic C), and the immobilized N from the straws of fertilized plots, especially of MNPK plot, was lesser, compared to unfertilized plots. Adding maize straw into soil increased the metabolic quotient (qCO2) of soil microorganisms, but the difference among the treatments was not significant. During incubation, the amounts of soil microbial biomass C and N from different treatments differed with time. Therefore, in agricultural practices, the differences in the nutrient contents of straw due to different fertilization should be considered when the straw was to be added into soil.

Soil samples were collected from a 17-year fertilization experiment site in southern Loess Plateau to study the effects of different fertilizations and fallowing on the characteristics of soil nitrogen mineralization, and the transformation of exogenous NO3(-) -N in sterilized and non-sterilized soil samples. The results showed that a combined application of manure and chemical NPK and long-term fallowing increased the contents of soil organic matter, total N, and mineralized N, as well as the N mineralization rate significantly, compared with the control. Applying chemical NPK increased soil inorganic N content, but had less effects on the contents of soil organic matter, total N and mineralized N, as well as the N mineralization rate. Autoclaved sterilization resulted in a significant increase of soil NH4(+) -N content, while soil NO3(-) -N content remained relatively constant whether sterilization or not, suggesting that under the conditions of our incubation, abiotic and biological factors had no significant effects on the transformation of exogenous NO3 (-) -N.

In this paper, soluble organic carbon (SOC) and nitrogen (SON) were extracted from manure, and their adsorption characteristics in Argosols and Anthrosols in Guanzhong region of Shaanxi Province were investigated. The results showed that the adsorption of SON and SOC in the two soils could be fitted by initial mass isotherm model, and the adsorbed amounts of SON and SOC had a significant linear relationship with the initial concentrations of SON and SOC added into soils. The partition coefficient, m of the initial mass isotherm model, indicated that Argosols had a higher adsorbility than Anthrosols. The average adsorption rates of SON and SOC in Anthrosols were 24.3% and 18.8%, and those in Argosols were 38.3% and 18.6%, respectively. The low adsorption rates of SON and SOC indicated their high mobility in the two soils, and more SON was adsorbed than SOC suggested the higher potential of SOC leaching from soil.