Nitrate leaching of winter wheat grown in lysimeters as affected by fertilizers and irrigation on the North China Plain

Proper application of nitrogen（N） fertilizers and irrigation management are important production practices that can reduce nitrate leaching into groundwater and improve the N use efficiency（NUE）. A lysimeter/rain shelter facility was used to study effects of the rate of N fertilization, type of N fertilizer, and irrigation level on key aspects of winter wheat production over three growing seasons（response variables were nitrate transport, N leaching, and NUE）. Results indicated that nitrate concentration in the soil profile and N leaching increased with the rate of N fertilization. At the end of the third season, nitrate concentration in the top 0–75 cm layer of soil was higher with manure treatment while urea treatments resulted in higher concentrations in the 100–200 cm layer. With normal irrigation, 3.4 to 15.3% of N from applied fertilizer was leached from the soil, yet no leaching occurred under a stress irrigation treatment. The manure treatment experienced less N leaching than the urea treatment in all cases except for the 180 kg N ha^-1 rate in 2011–2012（season 3）. In terms of grain yield（GY）, dry matter（DM） or NUE parameters, values for the manure treatment were lower than for the urea treatment in 2009–2010（season 1）, yet were otherwise higher for urea treatment in season 3. GY and crop nitrogen uptake（NU） were elevated when the rate of N fertilizer increased, while the NUE decreased; GY, DM, and NU increased with the amount of irrigation. Data indicated that reduced rates of N fertilization combined with increased manure application and proper irrigation management can lower nitrate levels in the subsoil and reduce potential N leaching into groundwater.

Use of the Nitrogen Index to assess nitrate leaching and water drainage from plastic-mulched horticultural cropping systems of Florida

Water quality in Florida is significantly impacted by nitrate(NO_(3)-N)leaching losses from agriculture in a large part of the state.Horticultural crops are planted across large areas of Florida on coarse sandy soils with low soil water retention and soil organic matter,increasing the potential for NO_(3)-N leaching.Nitrate leaching losses from the root zone of vegetable cropping systems can negatively impact groundwater.New tools such as the Nitrogen Index(N-Index)are able to quickly assess N use efficiency and losses via NO_(3)-N leaching from agricultural systems.Furthermore,the N-Index provides technical information about N losses pathways tied to agricultural management practices with a great level of confidence;this information has been used by researchers,growers and policymakers as a decision support system.However,the current version of the NIndex that has been used for different field crops has not been calibrated to be used in plastic-mulched horticultural cropping systems.The aim of this work was to calibrate and validate the N-Index for plasticmulched horticultural cropping systems of Florida.This study found that the N-Index tool accurately identified and ranked the risk of N losses in the evaluated horticultural systems.The N-Index was calibrated for Florida's plastic-mulched horticultural cropping systems using a sensitivity analysis.The adjusted N-Index was validated using compiled data of vegetables grown under plastic mulching systems during three consecutive seasons.Results from these studies suggest that the N-Index can be an easy-to-use tool capable of assessing nitrogen management practices for vegetable systems.The tool can be used to guide nutrient managers in the implementation of best nitrogen management practices that could contribute to reduced NO_(3)-N leaching losses from vegetable systems in Florida,contributing to a smaller environmental footprint and conservation of water quality.

Influences of nitrification inhibitor 3,4-dimethyl pyrazole phosphate on nitrogen and soil salt-ion leaching

An undisturbed heavy clay soil column experiment was conducted to examine the influence of the new nitrification inhibitor, 3,4- dimethylpyrazole phosphate （DMPP）, on nitrogen and soil salt-ion leaching. Regular urea was selected as the nitrogen source in the soil. The results showed that the cumulative leaching losses of soil nitrate-N under the treatment of urea with DMPP were from 57.5% to 63.3% lower than those of the treatment of urea without DMPP. The use of nitrification inhibitors as nitrate leaching retardants may be a proposal in regulations to prevent groundwater contaminant. However, there were no great difference between urea and urea with DMPP treatments on ammonium-N leaching. Moreover, the soil salt-ion leaching losses of Ca^2＋, Mg^2＋, K^＋, and Na^＋ were reduced from 26.6% to 28.8%, 21.3% to 27.8%, 33.3% to 35.5%, and 21.7% to 32.1%, respectively. So, the leaching losses of soil salt-ion were declined for nitrification inhibitor DMPP addition, being beneficial to shallow groundwater protection and growth of crop. These results indicated the possibility of ammonium or ammonium producing compounds using nitrification inhibitor DMPP to control the nitrate and nutrient cation leaching losses, minimizing the risk of nitrate pollution in shallow groundwater.

Effect of long-term fertilization on soil nitrate distribution

A thirteen years long-term field fertilizer experiment was conducted to monitor the effect of different fertilization on soil nitrate distribution. The results showed: (1) Applying relative excessive N fertilizer could result large quantities of NO3- residue and NO3- movement downward in soil profiles; amending phosphate fertilizer or organic manure with nitrogen fertilizer together could significantly improve the status of NO3- leaching downward due to the balanced uptake of nutrients by crops. ( 2) Appropriate amounts of nitrogen fertilizer which was equal or smaller than the optimal fertilization rate could not result in more NO3- leaching in Northern China. (3) Precipitation influenced the amounts and depth of soil NO3- leaching: NO3- could move to 80 cm depth or below at autumn or at the next spring when rainfall was higher during the rainy season through July to September in North China.

The characterization of soil profile distribution for nitrate leached in the paddy soil

Experiment was conducted for five successiveyears under large undisturbed monolith lysime-ters(2m×2m in square,l m in depth).Thesoil was silty clay loam texture and had a con-tent of total N 1.55 g/kg.The soil was flood-ed with penetration rate controlled at approxi-mate 3 mm per day in duration of double-riceseason and laid fallow and natural in winterand spring.Results showed that nitrate was the mainform of nitrogen in percolates.The change of

Evaluation of Pathway of Nitrogen Loss in Winter Wheat and Summer Maize Rotation System

The nitrogen loss pathway in winter wheat and summer maize rotation system was studied based on field experimental data. The results showed that nitrogen recovery rate was significantly decreased with nitrogen fertilization rate increased, while residual rate and losses rate had an increasing trend. Accumulated ammonia volatilization loss in winter wheat and summer maize rotation was 12. 8(N0), 22.0(N120), 33. 0(N240) and 64. 5 kg N ha-1 (N360) respectively and rate of ammonia volatilization loss was 3.8, 4.2 and 7.2% respectively while urea was mixed with 0 -10 cm soil or spread before irrigation. Denitrification loss with acetylene-soil core incubation method in winter wheat was lower than 1 kg N ha-1 and rate of denitrification loss was 0. 21 - 0. 26% or trace. Denitrification loss in summer maize was 1 - 14 kg N ha-1 and rate of denitrification loss was 1-5%. The total gaseous loss in winter wheat and summer maize rotation system was less than 10%, and the main nitrogen fertilizer loss way was leaching below 0 - 100 cm soil profile and accumulated in deeper soil.

Process optimization of rare earth and aluminum leaching from weathered crust elution-deposited rare earth ore with compound ammonium salts

In order to intensify the leaching process of rare earth（RE） and reduce the impurities in the leachate, ammonium chloride（NH4Cl） and ammonium nitrate（NH4NO3） were mixed as a compound leaching agent to treat the weathered crust elution-deposited RE ore. Effects of molar ratio of NH~＋_4Cl and NH_4NO_3, ammonium（NH_4） concentration, leaching agent pH and flow rate on the leaching process of RE were studied and evaluated by the chromatographic plate theory. Leaching process of the main impurity aluminium（Al） was also discussed in detail. Results showed that a higher initial ammonium concentration in a certain range could enhance the mass transfer process of RE and Al by providing a driving force to overcome the resistance of diffusion. pH almost had no effects on the mass transfer efficiency of RE and Al in the range of 4 to 8. The relationship between the flow rate and height equivalent to a theoretical plate（HETP） could fit well with the Van Deemter equation, and the flow rate at the lowest HETP was determined. The optimum conditions of column leaching for RE and Al were 1：1（molar ratio） of NH_4Cl and NH_4NO_3, 0.2 mol/L of ammonium concentration, pH 4–8 of leaching agent and 0.5 mL /min of flow rate. Under this condition, the mass transfer efficiency of RE was improved, but no change was observed for Al compared with the most widely used ammonium sulfate. Moreover, the significant difference value（around 20 mL） of retention volume at the peak concentration between RE and Al provided a possibility for their separation. It suggested the potential application of the novel compound leaching agent（NH_4Cl/NH_4NO_3）. It was found that the relative concentration of RE in the leachate could be easily obtained by monitoring the pH of leachate.

Optimizing Nitrogen Use Efficiency for No-Till Corn Production by Improving Root Growth and Capturing NO_(3)-N in Subsoil

Subsoil acidity restricts root growth and reduces crop yields in many parts of the world. More than half of the fertilizer nitrogen(N) applied in crop production is currently lost to the environment. This study aimed to investigate the effect of gypsum application on the efficiency of N fertilizer in no-till corn(Zea mays L.) production in southern Brazil. A field experiment examined the effects of surface-applied gypsum(0, 5, 10, and 15 Mg ha^(-1)) and top-dressed ammonium nitrate(NH_4NO_3)(60, 120, and 180 kg N ha^(-1)) on corn root length, N uptake, and grain yield. A greenhouse experiment was conducted using undisturbed soil columns collected from the field experiment site to evaluate NO_3-N leaching, N uptake, and root length with surface-applied gypsum(0 and 10 Mg ha^(-1)) and top-dressed NH_4NO_3(0 and 180 kg N ha^(-1)). Amelioration of subsoil acidity due to gypsum application increased corn root growth,N uptake, grain yield, and N use efficiency. Applying gypsum to the soil surface increased corn grain yield by 19%–38% and partial factor productivity of N(PFPN) by 27%–38%, depending on the N application rate. Results of the undisturbed soil column greenhouse experiment showed that improvement of N use efficiency by gypsum application was due to the higher N uptake from NO_3-N in the subsoil as a result of increased corn root length. Our results suggest that ameliorating subsoil acidity with gypsum in a no-till corn system could increase N use efficiency, improve grain yield, and reduce environmental risks due to NO_3-N leaching.

A nitrogen index for improving nutrient management within commercial Mexican dairy operations

Some intensive dairy operations in Mexico are contributing to large,negative environmental impacts,especially in regions dominated by high concentrations of animals.Excessive manure inputs plus additional nitrogen(N)fertilizer has,in some cases,resulted in background nitrate–nitrogen(NO3–N)levels in irrigation water that are so high,it is not safe for human consumption.One reason is that commercial farmers in this region are currently not using any method to rapidly calculate N budgets based on their practices,N inputs and/or crop N uptake.The Nitrogen Index,a quick tool that can be used to conduct an assessment within a few minutes,was developed for Mexico,but needed further testing under commercial field operations.We conducted studies in 2010 and 2011 and collected soil and crop information from several commercial farming operations to test the tool.The index accurately assessed(Po0.0001)residual soil nitrate after harvesting corn(Zea mays L.)and oats(Avena sativa L.);and also accurately assessed the N uptake of these crops(Po0.01).The Mexico N Index is a tool that can be used to quickly conduct N balances,show when N is being over-applied,and help reduce over-application,thus reducing N losses to the environment and improving management of dairy forage systems in Mexico.