[Effects of Fertilizer Application Strategy Adjustments on Nitrogen and Phosphorus Loss from Typical Crop Systems in Taihu Lake Region].

The intensity of crop farming fertilizer input is generally high in the Taihu Lake Region, with chemical fertilizer as the main form. Due to inappropriate fertilizer application, nitrogen and phosphorus loss have occurred, causing serious agricultural non-point source pollution. The Ministry of Agriculture and Rural Affairs of China has launched the "zero-growth action for chemical fertilizer use" and "replacement action with organic fertilizer" ("two actions" for short) campaigns since 2015. Local agricultural sectors adjusted fertilizer application strategies of crop farming to respond to the call of two actions. However, the current research is still focusing on reducing the total amount of fertilizer application and increasing the area of organic fertilizer application, which is mainly based on grain crops. The study of agricultural environment problems is still lacking, especially in vegetable, orchard, and tea systems. Therefore, a study was carried out in the typical agricultural area of Suzhou City Wuzhong District from 2019 to 2021. Based on the data of the amount of nitrogen and phosphorus removal by harvest crops and soil nitrogen and phosphorus residual in paddy, vegetable, orchard, and tea systems, the loss was estimated. The responses of nitrogen and phosphorus loss from typical crop systems to fertilizer application strategy adjustments were studied through analysis of different factors. The results showed that fertilizer application rate was the key to control nitrogen and phosphorus loss. Additionally, the suitable replacement ratio of organic fertilizer could further reduce the loss risk. It should be noted that the urgent demand for nutrients in crop growth should be considered to determine the timing of organic fertilizer application, and agricultural machinery should be used to assist organic fertilizer application to reduce labor output if possible. Fertilizer efficiency was the core of environmental friendliness and economic benefits of crop farming. Hence, improving fertilizer efficiency should be the guidance of fertilizer application strategy adjustment. Our suggestions on the adjustment of fertilizer application strategy in different crop systems in the study area are as follows:attention should be paid to the nitrogen, phosphorus, and potassium input ratio in paddy systems to further reduce nitrogen and phosphorus loss. Planting structure adjustment should be emphasized in vegetable systems to promote fertilizer efficiency. The strategy to satisfy both tea and orchard growth from a composite system perspective would help to build crop systems that meet the needs of green agricultural development.

[Effects of Warming and Fertilization on Soil Organic Carbon and Its Labile Components in Rice-wheat Rotation].

Farmland is the important soil carbon pool of terrestrial ecosystems and organic nutrient pool for crop growth. To clarify the impact of climate warming on the soil carbon pool, this study analyzed the effects of warming and fertilization on soil organic carbon and its labile components under rice-wheat rotation using a free-air temperature increase system. The variation in soil carbon pool management index (CPMI) was also evaluated. The results showed that the combined effects of warming and fertilization on soil organic carbon content and labile organic carbon components were insignificant. Warming increased the soil organic carbon (SOC) content, and the differences between warming and the ambient control in total organic carbon (TOC) and recalcitrant organic carbon (ROC) reached a statistically significant level. Compared with those under the ambient control, the contents of TOC, ROC, and labile organic carbon (LOC) subjected to warming increased by 7.72%, 7.42%, and 10.11%, respectively. The increased microbial biomass carbon (MBC) content (20.4%) and decreased particulate organic carbon (POC) content (36.51%) may have been the main reason for the variation in SOC. Warming showed no significant effect on soil dissolved organic carbon (DOC) content, whereas it markedly reduced its soluble microbial by-product components (41.89%). The results also showed that fertilization had no significant effect on soil TOC, ROC, and LOC, but it notably reduced the contents of DOC and POC and increased the MBC content. Compared with those under the control without fertilization, the contents of DOC and POC subjected to fertilization decreased by 35.44% and 28.33%, respectively, and the MBC content increased by 33.38%. Additionally, fertilization tended to increase the anthropogenic humus component (5.13%) and soluble microbial by-product component (29.41%) in dissolved organic matter and reduce the terrestrial humus component (13.33%). Warming and fertilization both tended to improve soil CPMI. Affected by SOC and LOC, the increase in soil carbon pool index and soil lability index were the main reason for the increase in soil CPMI under warming and fertilization, respectively. Overall, the results revealed that climate warming can affect the soil carbon pool by changing soil labile carbon components, which are not affected by fertilization.

[Effect of Deep Fertilization with Slow/Controlled Release Fertilizer on N Fate in Clayey Soil Wheat Field].

Clayey soil seriously affects water-holding capacity and nutrient movement. Adopting appropriate agronomic measures to optimize the distribution of soil inorganic nitrogen (SIN) and reduce the nitrogen (N) loss in this soil is the key to agricultural sustainable development. To clarify the effect of deep fertilization of slow/controlled release fertilizer with sowing on N loss in a clayey soil wheat field, two types of fertilizers, conventional fertilizer (CN) and slow/controlled release fertilizer (RCU), were selected in this study. Here, we evaluated the effects of these two fertilizer types on wheat yield, seasonal N runoff loss, ammonia volatilization, and N2O emissions in wheat fields in two typical fertilization modes (manual surface sowing and spreading (B) and belowground fertilization of slow/controlled release urea with mechanized strip sowing (D)). The temporal and spatial distribution characteristics of SIN in topsoil were also analyzed. The results showed that under the same fertilizer type, the wheat yield of D treatment was significantly higher than that of B treatment, whereas the yield of RCU was notably higher than that of CN under the same fertilization mode. D-RCU achieved the highest yield of 6.97 t·hm-2. The seasonal N losses from runoff and ammonia volatilization were higher than that from N2O emissions, and the responses of different N loss pathways to fertilizer types and fertilization methods were diverse. Fertilizer type and runoff occurrence time were the main influencing factors of N runoff loss, and N runoff loss of the RCU treatment was higher in the non-fertilization period. Unfortunately, affected by annual rainfall pattern, the seasonal N runoff loss of the RCU treatment (20.35 kg·hm-2) was significantly higher than that of the CN treatment (10.49 kg·hm-2). The late growth period was the main phase of ammonia volatilization, and the later period was jointly affected by fertilization modes and fertilizer types. The B-CN treatment induced the highest seasonal ammonia volatilization (18.15 kg·hm-2), which was significantly higher than that of the other treatments (7.31-8.38 kg·hm-2). Additionally, the D-RCU treatment (2.41 kg·hm-2) tended to reduce the N2O emissions in comparison to that in the B-CN treatment (4.02 kg·hm-2). The results also indicated that the horizontal movement of SIN was higher than the vertical movement. Deep fertilization of RCU was conducive to optimizing the spatial and temporal distribution of SIN, which was the main reason for the increase in wheat yield and the control of N loss from wheat fields. These results suggest that RCU is a suitable alternative fertilizer for increasing yield and reducing N loss in clayey soil wheat fields; D-RCU can increase the wheat yield and reduce ammonia volatilization and N2O emissions in wheat fields by optimizing the spatial and temporal distribution of SIN, and its increasing effect on N runoff loss in the non-fertilization period deserves attention.

[Effects of Wheat Straw Hydrochar and Its Modified Product on Rice Yield and Ammonia Volatilization from Paddy Fields].

Hydrochar can mitigate ammonia volatilization when applied in paddy fields due to its acidity and adsorption property. To realize the recycling of agricultural biowaste as well as the control of nutrient loss from paddy fields, a simulation soil-column experiment with wheat straw hydrochar (WHC) and water-washed hydrochar (W-WHC) was conducted to evaluate the performance of rice yield and ammonia volatilization from paddy fields. The results showed that WHC and W-WHC applied in paddy fields both increased the rice yield and the increased effect at low application rate (0.5%) was higher than that at high application rate (1.5%). In comparison with the control treatment (CKU), the rice yields achieved from low application rate treatments for WHC and W-WHC increased by 17.16% and 20.20% respectively. Except for the equal emission rate between W-WHC with low application rate and CKU treatments, hydrochar (WHC, W-WHC) addition reduced the ammonia volatilization from paddy fields when compared with the CKU. Among them, the ammonia volatilization levels from low-application WHC and high-application W-WHC treatments were significantly lower than that from the CKU treatment, reduced by 31.01% and 17.40%, respectively. Based on the analysis of ammonia volatilization during different fertilization stages, the control effect of hydrochar addition on ammonia volatilization was mainly benefited from tillering and panicle fertilizer stages. The change in the nitrogen concentration of surface water at the tillering fertilizer stage and in pH at the panicle fertilizer stage with the addition of hydrochar was the main driving factor for the reduction in ammonia volatilization. The results show that sufficient amounts of hydrochar derived from wheat straw application can increase crop yield while reducing ammonia volatilization from paddy fields. This method provides an effective route for recycling agricultural biowastes.

Effects of long-term fertilization without phosphorus on greenhouse gas emissions from paddy fields.

The strategy of few or no-phosphorus fertilization in rice season but more in wheat season can effectively increase phosphorus use efficiency and reduce phosphorus loss through runoff and leaching. It remains unknown whether the lack of phosphorus will affect greenhouse gas emission in the rice season. We monitored the CH4 and N2O emission fluxes during the growth period of rice treated with normal phosphorus application (NPK) and no-phosphorus application (NK) in two long-term experimental fields in Suzhou and Yixing. The results showed that long-term no-phosphorus application promoted CH4 and N2O emission in both fields. Compared with the NPK treatment, CH4 and N2O emissions from the NK treatment significantly increased by 57% and 25% in Suzhou experi-mental field, respectively, while those in Yixing experimental field were also significantly increased by 221% and 70%, respectively. The contents of organic acid, dissolved organic carbon and available phosphorus in soil were reduced under long-term NK treatment, and they were closely related to CH4 emission. Soil available phosphorus content was significantly negatively correlated with CH4 emission (r=-0.987). The global warming potential (GWP) was greater in NK treatment than NPK treatment in both fields. Therefore, long-term no-phosphorus application could decrease the contents of organic acid, soluble organic carbon, and available phosphorus in soils, resulting in more CH4 and N2O emission in rice field.

[Effects of Film Materials on Ammonia Volatilization Emissions from a Paddy System After Reducing Nitrogen Fertilizer Application].

Ammonia volatilization emissions constitute the main pathway of nitrogen loss from paddy systems. Present control technologies are based on reducing the amount of nitrogen fertilizer applied. However, ratio of nitrogen loss through ammonia volatilization emissions has not changed, and it has become a bottleneck for promoting nitrogen use efficiency. Therefore, in order to study the effects of film materials on ammonia volatilization emissions, a two-year field plot experiment was carried out with agricultural waste powder and amphipathic molecule materials spread on surface water after nitrogen fertilizer application in paddy system. The results showed that film materials could reduce nitrogen loss through ammonia volatilization by 19%-31% in the paddy season, and this part of nitrogen was accumulated in soil or assimilated by paddy tissue. The ammonium concentration and pH in the surface water and film materials were the major control factors of ammonia volatilization emissions with nitrogen fertilizer application. Moreover, further reductions in ammonia volatilization emissions could be achieved by film materials after reducing nitrogen fertilizer application. Differences in the effect mechanisms of the film materials provide flexible options for practical agricultural production to meet demands.

[Effects of Modified Biowaste-based Hydrochar on Rice Yield and Nitrogen Uptake].

Biochar application on farmlands is an efficient way to realize agricultural/forestry biowaste recycling in parallel with carbon sequestration. Recently, hydrochar produced by hydrothermal carbonization processes has attracted attention due to the advantages over conventional pyrolytic production (i.e., easier production process, higher carbon yield, reduced energy consumption, and lower flue gas emissions). To clarify the effects of hydrochar applied in farmlands on crop production, as well as to realize the recycling of agricultural/forestry biowaste resources, this study evaluated the effects of four types of modified-hydrochar addition on rice yield and nitrogen uptake in two typical soils and the possible influencing factors through soil-column experiments and material characterization. The results showed that sawdust hydrochar and/or straw hydrochar could increase rice yield and nitrogen uptake, as well as reduce N loss, in both treated soils after physical or biological modification, an effect that was independent of the application rate (5‰, 15‰; mass fraction). In comparison to the control, the rice yield and nitrogen uptake of hydrochar-addition treatments increased by 9.2%-20.7% and 7.7%-17.0% respectively. Sawdust hydrochar, with a wider C/N material, was conducive to improving nitrogen uptake in high fertility soils; meanwhile, the nitrogen utilization in low fertility soils was less affected by the type of hydrochar due to the limitations imposed by multiple factors. The results of material characterization showed that the surface of the hydrochar was rich in nutrients; the pore structure of hydrochar after washing or biological modification was greatly improved, the relative content of C was remarkably reduced, and the relative contents of N and O notably increased, which could affect nutrient fixation and supply. Thus, the improved pore structure and increased contents of N and O of modified hydrochars may be the key drivers for the increase in rice yield and nitrogen uptake with hydrochar addition. These results suggest that modified hydrochar is beneficial to realizing agricultural/forestry biowaste recycling and improving crop yield and nitrogen utilization, as well as reducing N loss from farmlands.

[Situation Analysis and Trend Prediction of the Prevention and Control Technologies for Planting Non-Point Source Pollution].

The contribution of crop planting to agricultural non-point source pollution should not be underestimated in China. Although many modern technologies have been developed to prevent non-point source pollution in recent decades, their impacts on pollution control in farmland are far from expectation. The application of technologies for non-point source pollution control for crop farming has been delayed due to unclear technical parameters and application effectiveness. Therefore, based on studies of the non-point source pollution control for crop farming in China and abroad that were published in the last 20 years, the present research was carried out to determine the development process of planting non-point source pollution control technologies and to illuminate the framework construction. The technologies in different fields and directions were compared by their effects on fertilizer input,yield, and pollutant emission. The development trend in the field of prevention and control technologies for planting non-point source pollution was subsequently predicted. In addition, a technical framework was developed with 3 fields (pollutant source reduction, pollutant interception in the migration process, and nutrient recycling) and 14 directions. The analysis showed that the technologies for reducing pollutants from the source have attracted the most (and increasing) concern with many research directions, and that many of the studies in this field have focused on the regulation of fertilizer application. On the contrary, there is a lack of technologies in the fields of pollutant process interception and nutrient recycling. Promoting nutrient-use efficiency, regulating nutrient transformation, and using soil supplements will be the main entry points for non-point source pollution control for crop farming. Furthermore, technologies will operate better with the help of farmland infrastructure and downstream purification systems.

[Fabrication of La-MHTC Composites for Phosphate Removal: Adsorption Behavior and Mechanism].

Lanthanum (La)-based materials have shown great potential for phosphate removal owing to the strong affinity between La and phosphate. In this study, magnetic hydrothermal biochar immobilized La(OH)3 (La-MHTC) were prepared and used as phosphate adsorbents. Hydrochar was produced by the hydrothermal carbonization process (220℃, 2 h). Magnetic La-MHTC with different La-to-Fe mass ratios were synthesized by the co-precipitation method. Subsequently, La-MHTC was applied to remove phosphate from wastewater. Results indicate that La-MHTC (with a La-to-Fe mass ratio of 2:1) exhibited excellent magnetic properties for easy recovery and high phosphate adsorption capacity up to 100.25 mg·g-1. Effective phosphate removal was obtained over a wide pH range of 3-10. The absorption isotherm and kinetics were better fitted by the Langmuir model and the pseudo second-order model, respectively, which showed a fast adsorption rate and exhibited superior La utilization efficiency. The La-MHTC has strong selectivity for phosphate in the presence of coexisting ions (Cl-, NO3-, and SO42-). The adsorption-desorption experiment suggested its excellent stability and cyclic utilization. In addition, La-MHTC was applied to treat real domestic wastewater, efficiently reducing the phosphate concentration (from 0.87 mg·L-1 to 0.05 mg·L-1). Electrostatic attraction and inner-sphere complexation between La(OH)3 and P via ligand exchange were the main mechanisms of phosphate adsorption by La-MHTC.

[Effect of Applying Hydrochar for Reduction of Ammonia Volatilization and Mechanisms in Paddy Soil].

Hydrochar, as a product of the hydrothermal carbonization of biomass, has good application prospects for the NH3 volatilization reduction in rice fields due to its rich pore structure and functional surface. In this study, hydrochar was applied as a soil conditioner to paddy soil. A soil column experiment was conducted to investigate the effect of hydrochar on NH3 volatilization throughout the growth period of rice. The experiment was conducted with three treatments:CKU (control without hydrochar); SHC (sawdust hydrochar); and W-SHC (water-washed sawdust hydrochar). The application rate of SHC and W-SHC was 0.5% (w/w). The study investigated the effects of different hydrochars on the pH and concentrations of NH4+-N in floodwater, the flux and accumulation of NH3 volatilization, and the yield-scale cumulative emission of NH3 volatilization. Results show that the SHC treatment significantly reduces cumulative emissions of NH3 volatilization and the yield-scale cumulative emissions of NH3 volatilization (P<0.05), which were 32.42% and 47.61% lower than CKU, respectively. The effect of W-SHC on ammonia volatilization reduction was slightly weaker, as the cumulative emissions of NH3 volatilization and the yield-scale cumulative emissions of NH3 volatilization decreased by 10.14% and 27.71%, respectively, compared with CKU. The NH3 volatilization reduction was possibly related to the disturbance of pH and the decrease in NH4+-N concentrations in the floodwater because of the application of hydrochar. Compared with CKU, both SHC and W-SHC treatments reduced the pH and NH4+-N concentration in the floodwater. The impacts were more obvious in the rice base fertilizer period (BF) and the first supplemental fertilizer period (SF1) than in the second supplemental fertilizer period (SF2). The soil urease activity was significantly inhibited by hydrochar (P<0.05), and the abundance of soil ammonia-oxidizing gene (AOA, AOB) also significantly increased after application of SHC (P<0.05). This resulted in the enhanced efficiency of ammonia-oxidizing, which had an effect on the reduction of the NH4+-N concentrations in the floodwater. This study provides theoretical and experimental data support for the application of hydrochar in agro-environments with regard to ammonia volatilization reduction in paddy fields.

[Effect of Two Soil Synergists on Ammonia Volatilization in Paddy Fields].

Nitrification inhibitor and biochar are commonly used as soil synergists. Among them, nitrification inhibitor can increase crop yields and N use efficiency, while biochar is a relatively new way of using biomass resources and has certain adsorption characteristics. In order to reduce nitrogen loss and environmental pollution caused by ammonia volatilization in paddy fields, a pot experiment with chemical fertilizer application (CN) as a control was conducted to study the effects of biochar (B), nitrapyrin (CP), and compound application (BCP) on pH, NH4+-N concentration dynamics in the flood water, rice yields, and ammonia volatilization from paddy fields. The results showed that the application of these two synergists had no significant effect on rice yields, and the nitrification inhibitors had a tendency to increase rice yields. The two synergists significantly increased ammonia volatilization from paddy fields, accounting for 25%-35% of the total N rate. Ammonia volatilization during periods of fertilizer application accounted for 86%-91% of the total loss, representing the main period of ammonia volatilization. Compared with the CN treatment, the CP treatment increased NH4+-N concentrations in flood water and the loss of ammonia via volatilization, which was increased by 59.18% and mainly occurred during a week after the basal fertilization(138%) and spike fertilization (48%), and non-fertilization stage (78%). Biochar had a promoting effect on ammonia volatilization with typically phased characteristics. The initial increasing effect of biochar on ammonia volatilization was higher than during the later stages, when NH4+-N concentrations and the pH of flood water showed the same trend. In addition, the coupling of nitrification inhibitor and biochar significantly increased the total loss of ammonia via volatilization loss due to the promotion effect of CP and B. The problem of increased ammonia volatilization loss caused by the application of nitrification inhibitors requires further research.

[Effects of sewage irrigation on growth of rice seedlings and soil environment with straw incorporation.] / 生活污水尾水灌溉对麦秸还田水稻幼苗及土壤环境的影响.

The effects of sewage irrigation on the growth of rice seedlings and soil environment under wheat straw returning were examined with a pot experiment. Root morphology, root activity, tiller number, plant height, dry matter accumulation of rice seedling, soil ferrous ions content, organic acid content and enzyme activity were measured. The results showed that sewage irrigation significantly increased the number of tillers and root activity at 41 days after transplanting under no N fertilizer application. Under the same N input level, sewage irrigation combined with N fertilizer promoted the growth of rice seedlings and root, and increased the root length, root surface area, root volume, root activity, tiller number and dry matter accumulation. Sewage irrigation significantly reduced the contents of soil ferrous ions and organic acid, while significantly increased the activities of soil urease and catalase. These results indicated that the combination of sewage irrigation and N fertilizer could effectively reduce the negative effect of straw returning on rice seedling and thus enhance soil fertility and quality.

[Effects of Returning Nitrogen by Biochar Loading on Paddy Growth, Root Morphology, and Nitrogen Use Efficiency].

Building a nutrient channel between eutrophic water and agricultural fields could reduce nutrient input into fields and alleviate eutrophication by returning nitrogen. In order to determine the feasibility of returning nitrogen by biochar loading, a rhizobox experiment was conducted with two nitrogen applied methods, namely SN (applied nitrogen by nitrogen fertilizer solution) and BN (applied nitrogen by nitrogen-loaded biochar). The results showed that BN, in comparison with SN, decreased the biomass and nitrogen uptake of the aboveground paddy by 16% and 14%, respectively, increased biomass root-shoot ratios by 25%-27%, and reduced nitrogen recovery use efficiency. Two nitrogen application methods affected the length and volume of paddy adventitious roots. Paddy underground biomass and nitrogen uptake were positively correlated with soil ammonium content, whereas paddy aboveground nitrogen uptake was negatively correlated with root tips. It was suggested that the paddy biomass and nitrogen uptake would be influenced when nitrogen was applied solely by nitrogen-loaded biochar. However, no affinity and no significance in nitrogen use efficiency were found for plant uptake between chemical nitrogen and biochar-loaded nitrogen. Additionally, biochar promoted soil mineral nitrogen content for further plant uptake. Therefore, biochar could be used as the carrier for returning nitrogen from waterbodies to fields. The replacement rate of chemical nitrogen fertilizer is the key to influencing plant growth and needs future study.

[Control Effect of Side Deep Fertilization with Slow-release Fertilizer on Ammonia Volatilization from Paddy Fields].

In order to reduce the ammonia volatilization in paddy fields, seven treatments were evaluated. These included three slow-release nitrogen fertilizers[sulfur-coated urea (SCU); resin-coated urea (RCU); release bulk blending fertilizer (RBB)], two fertilization modes[single base fertilization (B) and combined with panicle fertilizer (BF)], and conventional split fertilization (CN). The effects of side deep fertilization for slow-release nitrogen fertilizers on ammonia volatilization and surface water nitrogen dynamics were examined using a rice transplanter with a fertilizer sowing mechanism in the Taihu Lake region. The results showed that total nitrogen and ammonium nitrogen concentration in the surface water of the SCU treatment in the base period were higher, and those for RCU and RBB were lower than in the CN treatment. The cumulative ammonia volatilization during the whole rice season varied among different types of slow-release nitrogen fertilizers from 3.84% to 28.17% of the total N applied. The nitrogen loss from ammonia volatilization using the three slow-release nitrogen fertilizers was decreased when compared with conventional split fertilization. The ammonia volatilization loss exhibited the following relationship for the treatments:CN, B-SCU > BF-SCU, BF-RBB, BF-RCU, B-RBB, and B-RCU. When the slow-release nitrogen fertilizers were applied in single base fertilization, the total ammonia volatilization for the SCU was significantly higher than those for the RCU and RBB, while no significant differences were detected when these three slow-release fertilizers were combined with panicle fertilizer. Moreover, although the ammonia volatilization of BF-SCU was lower than that of B-SCU, those of BF-RCU and BF-RBB were higher than those with the B-RCU and B-RBB treatments, respectively. There are no significant differences for nitrogen volatilization when any of these three different fertilizers are applied as B or BF. The results for the emissions during ammonia volatilization during different stages indicated that the ammonia volatilization of SCU at the basal-tillering fertilization stage (7.54%) and the tillering-panicle fertilization stage (16.04%) were higher than those of the panicle fertilization-mature stage. The N loss from ammonia volatilization for RBB in the base-tillering fertilization stage (2.91%) increased more than in the tillering-panicle fertilization stage and panicle fertilization-mature stage. For RCU treatment, the highest rate for ammonia volatilization was detected at the panicle fertilization-mature stage (2.75%). Compared with the single base fertilization mode, ammonia volatilization during the panicle fertilization-mature stage was increased when combined with panicle fertilizer (BF) for the slow-release fertilizer. There was no obvious correlation between the N loss with ammonia volatilization for the three slow-release nitrogen fertilizers and the concentration of ammonium nitrogen in surface water during the panicle fertilization-mature stage.

[Influence of Calcium Carbonate and Biochar Addition on Soil Nitrogen Retention in Acidified Vegetable Soil].

In Taihu Lake region, more and more paddy fields are being converted to vegetable fields, which cause serious soil acidification and decreased soil nitrogen retention. In this study, calcium carbonate and biochar were used as acidification amendments to test their ability on soil acidification remediation and soil nitrogen retention improvement. Calcium carbonate and biochar addition rates were determined by pH buffering curves. An incubation experiment with and without nitrogen fertilization and multi-leaching simulation tests were conducted. The soil nitrogen mineralization rate, dynamics of the nitrogen content in soils and leachates, and soil pH were measured. The results showed that 3.92×10-2 mol·kg-1 calcium carbonate and 27.73 g·kg-1 biochar should be added into the tested acidified vegetable soil to recover the original pH value. Without nitrogen fertilization, the addition of calcium carbonate increased the soil nitrogen mineralization rate by 37% but had no significant effect on mineral nitrogen content. However, biochar addition significantly improved the soil nitrogen mineralization rate by 35%-44% and nitrate content by 42%-58%. Nitrogen leaching loss was cut down by 42%-57% in biochar addition treatment because of the lower leachate volume and nitrogen concentration, while calcium carbonate addition increased nitrogen leaching loss by 12%-76% because of the higher leachate nitrogen concentration. After leaching, the soil pH decreased for all the treatments. The soil pH change was the lowest for calcium carbonate addition treatment under no nitrogen fertilization and the lowest for biochar addition treatment under nitrogen fertilization. This result suggests that calcium carbonate is more applicable for seriously acidified soils which are fallowed and biochar is more suitable for the intensified vegetable fields because it can improve the soil nitrogen retention and soil pH, and reduce the nitrogen leaching loss.

[Effect of Straw Incorporation and Domestic Sewage Irrigation on Ammonia Volatilization from Paddy Fields].

A pot experiment was conducted to study the effect of straw returning and domestic sewage irrigation on the dynamics of NH4+-N concentration and pH in the flood water, and ammonia volatilization of paddy fields. The results showed that the NH4+-N concentration in flood water was significantly increased by wheat straw returning while significantly decreased by domestic sewage irrigation. The cumulative ammonia volatilization in the whole rice season under tap water irrigation and straw removal treatment was 58.29 kg·hm-2, accounting for 24.29% of the total N applied. The N loss ratio of ammonia volatilization was significantly increased to 45.66% by wheat straw returning, while significantly decreased to 17.26% under straw removal and 32.72% under straw returning by domestic sewage irrigation. Significant positive interaction was observed between straw incorporation and domestic sewage irrigation on ammonia volatilization loss. The average N loss from ammonia volatilization during the tillering stage was the highest among the three fertilization stages, accounting for 7.38%-24.44% of the total N applied. In addition, ammonia volatilization fluxes showed a significant positive correlation with the flood water NH4+-N concentration, irrespective of the irrigation water, but had no significant correlation with pH. These results indicated that straw returning increased ammonia volatilization losses, whereas domestic sewage irrigation could effectively reduce ammonia volatilization losses and simultaneously replace 44.41% of chemical nitrogen fertilizer by the N contained in the domestic sewage. The combination of domestic sewage irrigation and straw returning would be an ecological and environmental-friendly measure for rice nitrogen management in Taihu Lake region.

[Further reduction of nitrogen fertilizer application in paddy field under green manuring of Taihu Area, China].

This study focused on the nitrogen loss via runoff, change of nitrogen in different forms in surface water in paddy field, and grain yield, through further reduction of nitrogen fertilizer application rate under green manuring without basal dressing. Results showed that with 150 kg · hm(-2) inorganic N fertilizer input after return of green manure to soil, no basal dressing could not only sharply reduce N concentration in surface water and decrease 17.2% of N loss, but also increase 2.8% of grain yield in comparison with basal dressing. It was a worthwhile farming method that inorganic nitrogen fertilizer was not used for basal dressing but for topdressing after return of green ma- nure to soil in Taihu Area. However, the grain yield would decrease if the rate of topdressing nitro- gen was excessively reduced or increased. After all, it was feasible to realize harmonization of grain yield and environmental benefits in Taihu Area, with 133 kg · hm(-2) inorganic N fertilizer input after return of green manure to soil as well as no application of basal dressing, which could greatly reduce N fertilizer input and N loss as well as ensure rice yield.

[Nitrogen balance and environmental impact of paddy field under different N management methods in Taihu Lake region].

Effects of nitrogen (N) management methods of paddy field on N export to environment and paddy N balance in Taihu lake region, China were studied. Field experiment including site-specific nitrogen management (SSNM), organic & chemical N fertilizer treatment (OCN), control released urea treatment (CRN), reduced chemical N treatment (RN) and farmer's N treatment (FN) were conducted at the Taihu lake region in 2008. N loss including runoff, leaching, ammonia volatilization and N2O were calculated, and the N balance was evaluated. Results showed the grain yield of SSNM, OCN, CRN and RN treatments was identical with FN treatment, while the total N rate reduced about 20%-40%, and N use efficiency (NUE) increased 14.5%-44%. N export of SSNM and CRN treatments decreased 52.8% and 45.4% in comparison with FN treatment. Under the same N input, N export of OCN treatment was lower than pure chemical N treatment (RN). N surplus was observed in FN treatment, while N deficit existed in SSNM treatments. CRN and SSNM treatments could increase NUE, reduce N export without sacrifice of yield and benefit, and could be as an economic and environment-friendly measure to intensify in Taihu lake region.

[Nondestructive determination of nitrate content in spinach leaves with visible-near infrared high spectra].

The objective of the present research was to study the potential of Vis-NIR (visible-near-infrared) high spectra for nondestructive determination of nitrate content in spinach leaves. Five different nitrogen treatments were carried out to achieve a wide range of nitrate content in spinach leaves. The leaf reflectance was measured between 350 to 2,500 nm with a 1 nm step with a leaf clip by ASD Fieldspec FR spectroradiometer, and the nitrate content was measured by spectrophotometric method (National Standard Method of P. R. China). Statistical models were developed using partial least squares (PLS) and principal component regression (PCR) analysis technique, different mathematical treatments for spectra processing such as smoothing, first and second derivative analysis, baseline correction, multiplicative scatter correction (MSC), and standard normal variate correction (SNV), and different wavelength ranges were compared to determine the best model. The dataset was separated into two parts: one used for calibration (n=43), and the other used for test (n=15). First, the model was calibrated and cross-validated with the calibration dataset, then the model was validated with the test dataset to test its prediction ability. The results showed that smoothing, first derivative and second derivative analysis can improve the prediction obviously, while other spectra pre-processing technique e. g. baseline correction, MSC and SNV technique can improve the prediction little. PCR analysis could get better modeling results than PLS analysis. The best model was obtained with the spectra first processed by smoothing then by first derivative change in the full range (350-2,500 nm). Test of the best PLS model and PCR model with an independent dataset exhibited a good agreement between the predicted and observed values, with the correlation coefficient of 0.94 for PLS model and 0.95 for PCR model, and the prediction RMSE was 128.2 mg x kg(-1) for PLS model and 120.8 mg x kg(-1) for PCR model, respectively. These results indicate that visible-NIR spectra technique is a feasible, nondestructive way to predict the nitrate content in spinach leaves.

[Humus composition and stable carbon isotope natural abundance in paddy soil under long-term fertilization].

Soil samples were collected from an experimental paddy field with long-term (26 years) fertilization in Taihu Lake region of Jiangsu Province to study the effects of different fertilization on the organic carbon distribution and stable carbon isotope natural abundance (delta 13C) in the soil profile, and on the humus composition. The results showed that long-term fertilization increased the organic carbon content in top soil significantly, and there was a significantly negative exponential correlation between soil organic carbon content and soil depth (P < 0.01). The organic carbon content in 10-30 cm soil layer under chemical fertilizations and in 20-40 cm soil layer under organic fertilizations was relatively stable. Soil delta 13C increased gradually with soil depth, its variation range being from -24% per thousand to -28 per thousand, and had a significantly negative linear correlation with soil organic carbon content (P < 0.05). In 0-20 cm soil layer, the delta 13C in treatments organic manure (M), M + NP, M + NPK, M + straw (R) + N, and R + N decreased significantly; while in 30-50 cm soil layer, the delta 13C in all organic fertilization treatments except R + N increased significantly. Tightly combined humus (humin) was the main humus composition in the soil, occupying 50% or more, and the rest were loosely and stably combined humus. Long-term fertilization increased the content of loosely combined humus and the ratio of humic acid (HA) to fulvic acid (FA).