Effect of humic and calcareous substance amendments on the availability of cadmium in paddy soil and its accumulation in rice.

Humic substances (HS) are widely known as important components in soil and significantly affect the mobility of metals due to their large surface area and abundant organic functional groups. Calcareous substances (CSs) are also commonly used as robust and cost-effective amendments for increasing the pH of acidic soils and decreasing the mobility of metals in soils. In this study, we developed a new remediation scheme for cadmium (Cd)-contaminated soil remediation by coupling HS and CS. The results showed that regardless of the addition of fulvic acid (FA), all the CS-containing treatments significantly increased the soil pH by 0.32-0.60, and the concentration of bioavailable Cd decreased in the moderately (field experiment soil, maximum 62%) and highly (pot experiment soil, maximum 57%) Cd-contaminated soils. The Cd content in rice (Oryza sativa L.) tissues significantly decreased after all the treatments. The bioaccumulation factors (BAFs) decreased by over 50% in the roots, stems, leaves and husks in all treatments, while the translocation factors (TFs) only significantly decreased in the highly contaminated soil. Among all treatments, the two HS+CS treatments (FA+CaCO3 and FA+CaO) had the greatest effect on decreasing the concentration of bioavailable Cd in soil and Cd in brown rice grains. The suggested mechanism for the effectiveness of coupled HS and CS was that CS first mitigated the pH and precipitated Cd, followed by a complexation effect between HS and Cd. Although the Cd in rice grains in both cases was higher than the standard limit, HS+CS remediation can be advocated as a robust, simple and cost-effective scheme for Cd remediation if the additive dose is slightly increased, as this approach can simultaneously improve the pH of acidic soil and adsorb Cd in soil.

Dynamics of soil bacteria and fungi communities of dry land for 8 years with soil conservation management.

Microorganisms play an important role in nutrient cycling and ecosystem stability. This experiment studied the conservation management approaches [control without fertilizer (CK); fertilizer and different mulching based straw mulching (SM), plastic mulching (PM), ridge-furrow with plastic mulching (RFPFM), and green manure (GM)] effects on the soil microbial community structures in spring corn (Zea Mayis) dry land. The results showed that the bacterial phylum mainly included Proteobacteria (28.2%-36.8%), Acidobacteriota (9.1%-17.9%), Bacteroidota (5.6%-8.9%) and Actinobacteria (3.1-6.2%). The most richness fungal components were Ascomycota (35.2%-44.2%), Basidiomycota (3.3%-12%) and Mortierellomycota (3.4%-6.6%). Additionally, the highest Chao1 and abundance-based coverage estimator (ACE) indexes of bacteria (2931.9 and 2953.7) and fungi (1083.316 and 1100.650) were present in RFPFM that indicating the richest microbial abundance, the highest Shannon and Simpson indexes was exist in PM (9.332 and 0.996) for bacteria and RFPFM (6.753 and 0.974) for fungi. Therefore, this study reveals the conservation management of fertilizer addition and mulching management obviously promoted microbial diversity and altered the superior microbial distribution that provides a potential way for agricultural sustainable management approaches in production practice during circular economy.

Evaluation of N2O emission from rainfed wheat field in northwest agricultural land in China.

The net greenhouse gas (NGHG) emissions and net greenhouse gas intensity (NGHGI) were investigated via the determination of nitrous oxide (N2O) emission in loess soil under rainfed winter wheat monocropping system during 3 years of field study in Northwest China. Five treatments were carried out: control (N0), conventional nitrogen (N) application (NCon), optimized N application with straw (SNOpt), optimized N application with straw and 5% of dicyanodiamide (SNOpt + DCD), and optimized N rate of slow release fertilizer with straw (SSRFOpt). Over a 3-year period, the NGHG emissions were achieved 953, 1322, 564, and 1162 kg CO2-eq ha-1, simultaneously, and the NGHGI arrived 158, 223, 86, and 191 kg CO2-eq t-1 grain in NCon, SNOpt, SNOpt + DCD, and SSROpt grain, respectively. Contrasted with conventional farming system, optimized farming methods reduced 32% of N fertilizer use without significant decrease in grain yield, but brought about 38% increase in N2O emissions, up to 28% gained in soil CH4 uptake. Thus, it was observed that the straw incorporation performs noticeable increased in N2O emissions in the winter wheat cropping season. Among the optimized N fertilizer rates compared with the SNOpt treatment, the SNOpt +DCD and SSROpt treatments decreased in N2O emissions by approximately 55% and 13%, respectively. Additionally, the N2O emission factor across over a 3-year period was 0.41 ± 0.08% derived from N fertilizer, and it was half of IPCC default values for upland corps. It is expected possibly due to low precipitation and soil moisture with the monocropping system. The 25% higher in the amount of rainfall (almost 300 mm in 2013-2014) during a cropping season underwent into 1-2-fold increase in N2O emissions from N-fertilized plots. As the statistical differences among annual cumulative emissions coincided with that during winter wheat growing season, it can be concluded that crop growing season is a vital important period for the determination of N2O emissions from under rainfed monocropping system.

[Effect of planting white clover on nutrients and biological properties of soils in persimmon orchard of Weibei, Shaanxi Province, China]. / é™•è¥¿æ¸­åŒ—æŸ¿å­å›­ç§æ¤ç™½ä¸‰å¶è‰å¯¹åœŸå£¤å »åˆ†å’Œç”Ÿç‰©å­¦æ€§è´¨çš„å½±å“.

Leguminous crop planting is one of the most important managements in sustainable agriculture, which has the potential to improve soil quality and environmental health by increasing N input and facilitating soil and water conservation. In this study, effects of white clover planting on soil nutrients and biological properties in persimmon orchard was investigated to understand its potential effects on improvement of soil fertility and economic performance. Soil samples were collected on September 14th, 2017 at 0-10 cm, 10-20 cm, 20-30 cm and 30-40 cm soil depth in two treatments (i.e. ploughing with no grass and planting white clover) in persimmon orchard, and were analyzed for soil available nitrogen, organic matter, microbial biomass carbon and nitrogen, and enzyme activity. Compared to the control, soil available nitrogen, organic matter, microbial biomass carbon and nitrogen, and the activities of urease, sucrase, catalase and alkaline phosphatase all increased in grass treatment. Specifically, in grass planting treatment, soil organic matter and microbial biomass carbon were significantly increased at 0-10 cm soil, and increased soil avai-lable nitrogen was found at 10-20 cm soil. For enzyme activity, significantly elevated urease activity exhibited at surface depth (0-20 cm), while catalase, sucrase activity and geometric mean (GME) of enzyme activity were higher within entire tested soil profile (0-40 cm). Overall, our results indicated white clover planting in orchard could not only facilitate soil fertility, but also reduce chemical fertilizer input and improve economic benefit, which could be considered as a good orchard cultivation mode.

Ridge-furrow with plastic film and straw mulch increases water availability and wheat production on the Loess Plateau.

Mulching is critical for increasing water availability and hence winter wheat production in dryland farming systems. A two-year study was conducted to assess the effects of mulches on soil water storage (SWS), temperature, water use efficiency (WUE) and yields of winter wheat on the Loess Plateau. Four treatments were examined: conventional flat planting (CK), straw mulch (FPS), transparent plastic film mulch (FPP) and ridge-furrow with plastic film-mulched ridge and straw-mulched furrow (RFPS). Compared with CK, RFPS greatly increased SWS from 0-60 cm, FPP increased SWS from 0-40 cm, and FPS slightly increased SWS from 0-60 cm; however, FPP significantly (P < 0.05) decreased SWS from 61-100 cm. RFPS and FPP increased soil temperatures in cold seasons relative to CK, especially in RFPS (2.0-2.3 °C). Meanwhile, the rate of soil temperature increase was greater in RFPS and FPP than in CK but was lower in FPS. Mean yields were significantly increased in RFPS (56.78%), FPP (44.72%) and FPS (9.57%), and WUE was significantly increased in RFPS (44.04%) and in FPP (37.50%) compared with CK (P < 0.05). We conclude that ridge-furrow planting with plastic film-mulched ridge and straw-mulched furrow has a good potential for raising winter wheat production on the Loess Plateau.

A two-year field study of phytoremediation using Solanum nigrum L. in China.

A two-year in-situ phytoremediation trial was launched in Shenyang Zhangshi (Sewage) Irrigation Area (SZIA). The phytoremediation efficiency of Solanum nigrum L. was determined, by both monitoring the change of soil Cadmium level in the upper 20 cm of soil, and calculating the plant uptake of soil Cd. After two years experimental, by monitoring the soil Cd concentrations, The Cd concentrations decreased on average from 2.75 mg kg(-1)to 2.45 mg kg(-1) in the first year and from 2.33 mg kg(-1) to 1.53 mg kg(-1) in the second year, amounting to a decrease by a factor of 10.6% in the first year and 12% in the second year. After two years phytoremediation by S. nigrum, Cd concentrations of the seven experimental plots with S. nigrum growth decreased from 2.75 mg kg(-1) to 1.53 mg kg(-1), a decrease by a factor of 24.9%. And the soil Cd concentration decreased only 2.1% and 1.7% in the bared experimental plot. And the calculating of Cd uptake by S. nigrum shown that, the plants uptake 4.46% and 5.18% of the total soil Cd in 2008 and 2009, while the soil Cd concentrations decreased by a factor of 10.6% in 2008 and 12.1% in 2009.

High nitrogen deposition in an agricultural ecosystem of Shaanxi, China.

Atmospheric nitrogen (N) deposition plays an important role in the global N cycle. Data for dry and wet N deposition in agricultural ecosystem of Shaanxi in China is still imperfect; in this study, we continuously measured concentrations and fluxes of dry N deposition from 2010 to 2013 in Yangling district of Shaanxi province and wet N deposition from 2010 to 2012. The average annual concentrations of NH3, NO2, HNO3, particulate ammonium, and nitrate (pNH4 (+) and pNO3 (-)) varied among 3.9-9.1, 6.6-8.0, 1.2-1.4, 3.1-4.3, and 3.3-4.8 µg N m(-3), respectively, with mean values of 6.0, 7.2, 1.3, 3.8, and 4.1 µg N m(-3), respectively, during the entire monitoring period. The annual NH4 (+)-N and NO3 (-)-N concentrations in precipitation ranged 3.9-4.3 and 2.8-3.4 mg N L(-1) with the mean values of 4.1 and 3.3 mg N L(-1). The NH4 (+)-N/NO3 (-)-N ratio in rainfall averaged 1.2. Dry N deposition flux was determined to be 19.2 kg N ha(-1) year(-1) and the wet N deposition flux was 27.2 kg N ha(-1) year(-1). The amount of total atmospheric N deposition (dry plus wet) reached 46.4 kg N ha(-1) year(-1), in which dry deposition accounted 41 %. Gaseous N deposition comprised over 75 % of the dry deposition, and the proportion of oxidized N in dry deposition was equal to the reduced N. Therefore, the results suggest that more stringent regional air pollution control policies are required in the target area and that N deposition is an important nutrient resource from the atmosphere that must be taken into consideration in nutrient management planning of agricultural ecosystems.

Cadmium uptake in above-ground parts of lettuce (Lactuca sativa L.).

Because of its high Cd uptake and translocation, lettuce is often used in Cd contamination studies. However, there is a lack of information on Cd accumulation in the above-ground parts of lettuce during the entire growing season. In this study, a field experiment was carried out in a Cd-contaminated area. Above-ground lettuce parts were sampled, and the Cd content was measured using a flame atomic absorption spectrophotometer (AAS). The results showed that the Cd concentration in the above-ground parts of lettuce increased from 2.70 to 3.62mgkg(-1) during the seedling stage, but decreased from 3.62 to 2.40mgkg(-1) during organogenesis and from 2.40 to 1.64mgkg(-1) during bolting. The mean Cd concentration during the seedling stage was significantly higher than that during organogenesis (a=0.05) and bolting (a=0.01). The Cd accumulation in the above-ground parts of an individual lettuce plant could be described by a sigmoidal curve. Cadmium uptake during organogenesis was highest (80% of the total), whereas that during bolting was only 4.34%. This research further reveals that for Rome lettuce: (1) the highest Cd content of above-ground parts occurred at the end of the seedling phase; (2) the best harvest time with respect to Cd phytoaccumulation is at the end of the organogenesis stage; and (3) the organogenesis stage is the most suitable time to enhance phytoaccumulation efficiency by adjusting the root:shoot ratio.

[Effects of reducing N, straw returning and dicyandiamide application on winter wheat yield and nitrogen budgets in rain-fed region.] / 减氮-ç§¸ç§†è¿˜ç”°åŠåŒæ°°èƒºæ–½ç”¨å¯¹æ—±åœ°é›¨å »åŒºå†¬å°éº¦äº§é‡å’Œæ°®å¹³è¡¡çš„å½±å“.

In a 3-year field experiment, effects of reducing N fertilizer, straw returning and dicyandiamide (DCD) application on wheat yield and nitrogen budgets under wheat-fallow system were studied in rain-fed region. The experiment was carried out in Yangling of Shaanxi Province, and 4 treatments were installed including no nitrogen (CK), 220 kg N·hm-2 and no straw returning (FP), 150 kg N·hm-2 and straw returning (OPT), 150 kg N·hm-2, 7.5 kg·hm-2 DCD and straw returning (OPT+DCD). The results showed there was no remarkable difference for wheat yield between OPT and FP, but the N use efficiency of the former was 6.1% more than that of the latter, and the apparent N loss ratio was 7.2% less. OPT+DCD increased the average yield of winter wheat by 10.4% and 7.9% respectively compared to OPT and FP, the N use efficiency of winter wheat increased by 20.8% and 28.1%, and the apparent N loss ratio decreased by 8.5% and 15.1%, respectively. NH4+-N content in 0-20 cm of soil increased, accordingly the NO3--N content decreased in 40 to 45 days when DCD was applied.

[Research advances in the calculating method of nitrogen use efficiency (NUE) in cultivated lands].

Nitrogen use efficiency (NUE) has received worldwide concern in the sphere of agronomic science and environmental science, and it is fundamentally important for evaluating N utilization status and optimizing N fertilization management in cultivated lands. In recent years, in consideration of low values and great variations of NUE in China' s cultivated lands, some scholars have discussed on the traditional concept and calculating method of NUE, and also have proposed some substituted NUE calculating methods. In this paper, we summarized some disadvantages of both conventional concept and calculating method of NUE, i.e. the subtraction method and the 15N labeling method. Furthermore, we particularly introduced several substituted NUE calculation methods and discussed research directions in the future. In summary, we strongly suggested the establishment of a comprehensive evaluation index system of N utilization in good accordance with the current agricultural production status in China, based on a correct understanding of the dialectical relationships among N application rate, crop yield, N utilization and N loss.

Potential of Gibberellic Acid 3 (GA3) for Enhancing the Phytoremediation Efficiency of Solanum nigrum L.

A microcosm experiment with artificially contaminated soils was conducted in a greenhouse to evaluate the effect of gibberellic acid 3 (GA3) on phytoremediation efficiency of Solanum nigrum L. The GA3 was applied at three different concentrations (10, 100, 1000 mg L(-1)) to S. nigrum. Results indicated that GA3 can significantly (p < 0.05) increase the biomass of S. nigrum by 56 % at 1000 mg L(-1). Concurrently, GA3 application increased Cd concentrations in the shoot of S. nigrum by 16 %. The combined effects resulted in an increase in the amount of Cd extracted by a single plant by up to 124 %. Therefore, it is possible to use GA3 to promote the Cd phytoremediation efficiency of S. nigrum.

[Effects of different potassium fertilizer application periods on the yield and quality of Fuji apple].

In order to ascertain the effects of potassium fertilizer application periods on apple production, we conducted a field experiment and analyzed the differences in apple yield, fruit quality, potassium fertilizer use efficiency, and nutrient concentrations in leaves and fruits among treatments with differences in timing of potassium application. The results indicated that, compared with no potassium-applied treatment (CK), all potassium fertilizer application treatments significantly increased the apple yield by 4.3%-33.2%, meanwhile, it also obviously improved the fruit quality. In comparison with the application of 100% potassium fertilizer as a base, the application of 50% or 100% of potassium fertilizer at the fruit enlargement stage (the remaining 50% applied as a base or after flowering) significantly increased the apple yield by 20.5% - 27.7% and improved the fruit quality. Compared with the application 100% potassium fertilizer at the stage of fruit enlargement, the evenly split application as base flowering stage and at the fruit enlargement: stage not only contributed to a higher yield, better quality and higher potassium use efficiency, but also maintained a relatively stable potassium concentration level in leaves. However, the split potassium fertilizer application at the flowering and fruit enlargement stages resulted in the significant decrease in concentration of calcium in fruit, which would be negative to fruit quality. In conclusion, our research suggested that evenly split application of potassium fertilizer as a base and at the fruit enlargement stage was the suitable period for apple production in Fuji apple orchards in this region.

[Discussion on the calculation method of nitrogen use efficiency (NIUE) in long-term field experiments under wheat and maize rotation systems].

In recent years, some scholars from China have deeply discussed about the concept, connotation and calculating method of nitrogen use efficiency (NUE), and have raised questions and also put forward some improved methods for NUE calculation in cultivated lands. In this paper, we compared advantages and disadvantages of these improved NUE calculation methods by using the data from a 5-year positioning field experiment under a wheat-maize rotation system. The results indicated that it made mistakes when the traditional subtraction method was used to calculate NUE for wheat season and maize season separately, since the soil fertility level of experimental plots had differed significantly from each other after several seasons or years of different fertilization managements. Additionally, the calculated NUE increased markedly with the cropping season going, thus making it difficult to mirror the actual situation of N utilization in cultivated lands. For the wheat-maize rotation system, the cumulative NUE calculation method considered wheat season and maize season as a whole part, and skillfully avoided mistakes which could be caused by inhomogeneity of soil fertility levels between experimental plots. Moreover, the calculated NUE were comparably smaller, with smaller coefficient variations (CVs), in contrast with the traditional subtraction method. The NUE calculated by using the ratio method were bigger, with the smallest CVs, than that computed by using the cumulative calculation method. The soil N balance method took a thoughtful consideration about the budgets and losses of soil nutrients before and after crop growth, but obtained the largest values of NUE and CVs within these methods.

Phytoremediation potential of Solanum nigrum L. under different cultivation protocols.

In this study, Solanum nigrum L. was used as a hyperaccumulator for remediation of cadmium contaminated soil, and 3 different cultivation protocols were investigated. The results showed that a double cropping treatment enhanced the phytoremediation efficiency significantly, since it increased the amount of Cd extracted in one growing season by a factor of 1.62 compared to single cropping. However, the labor cost for double cropping was twice that of single cropping. If the time consumed is considered as a cost of phytoremediation, the double cropping treatment might be considered as an effective and economic cultivation protocol by reducing the overall time required to reach the targeted soil quality.

[Effects of different long-term fertilization patterns on Fuji apple yield, quality, and soil fertility on Weibei Dryland, Shaanxi Province of Northwest China].

A 7-year (2003-2010) located field experiment was conducted to evaluate the effects of different long-term fertilization patterns on the Fuji apple yield, quality, and soil fertility on the Weibei Dryland, Shaanxi Province of Northwest China. Seven treatments were installed, i. e., no fertilization (CK), inorganic P and K fertilization (PK), inorganic N and K fertilization (NK), inorganic N and P fertilization (NP), inorganic N, P, and K fertilization (NPK), swine manure (M), and half inorganic N, P, and K combined with half swine manure (NPKM). Each treatment had three replications. Fertilization increased the apple yield. The average yield in the 7 years under fertilization was increased by 14.4%-63.8%, as compared to the CK. The average yield decreased in the order of NPKM > NPK > or = M > NP > or = NK > PK > CK. In treatments NPKM, M, and NPK, the fruit sugar/acid (S:A) ratio, vitamin C, soluble solid, and hardness tended to be increased with time, with a smaller yearly fluctuation in treatments NPKM and M. In treatment NPKM, the S:A ratio and vitamin C increased by 30.9% and 17.5%, respectively after five years, as compared to the CK. Long-term rational fertilization increased the soil organic matter (SOC) content in 0-20 cm layer, with the largest increment in treatments NPKM and M (28.8% and 29.3%, respectively). The soil available N, P, and K contents in all layers in treatments NPK, NPKM, and M increased significantly, and the soil available N content in 0-20, 20-40, and 40-60 cm layers in treatment NPK was increased by 22.7%, 37.3%, and 53.4%, respectively. As compared to treatment NPK, the soil available P content in treatment NPKM was increased by 18.7%. In all fertilization treatments, the soil available Pcontent was significantly higher in upper layer than in lower layer.

[Present situation of rice fertilization in qin-ba mountainous area of Southern Shaanxi, China].

In order to understand the present situation of rice fertilization and the existing problems in the farmers' nutrient resources input in the Qin-Ba mountainous area of southern Shaanxi, the survey data from 2854 households in 11 counties of this area in the project "soil testing and formulated fertilization in 2006-2009" were analyzed and evaluated, and the countermeasures for the existing problems in the farmers' nutrient resources input were proposed. In the study area, the average rice yield was 7822 kg x hm(-2) per year, and the ratio of the households obtained the medium level yield was up to 50.9%. The input of the total fertilizers N, P2O5, K2O was 169, 68, and 54 kg x hm(-2), and the chemical fertilizer rate was 159, 62, and 45 kg x hm(-2), with the partial factor productivity (PFP) of the N, P2O5, and K2O being 51.52, 135.69, and 158.26 kg x kg(-1), respectively. According to the nutrient fertilization level, the proportion of the households fertilized with rational level of chemical N, P2O5, and K2O occupied 48.0%, 42.4%, and 7.2%, that of the households fertilized with excessive level was 22.6%, 11.2%, and 0.6%, and the proportion of the households fertilized with insufficient level occupied 29.4%, 46.5%, and 92.2%, respectively. The rice yield in the Qin-Ba mountainous area could be increased by 77 thousand tons if the households fertilizing with insufficient level of chemical NPK fertilizers increased the fertilization rate to a rational level. The existing problems in the farmers' nutrient resources input were mainly the coexistence of excessive and insufficient application of nitrogen and phosphate fertilizers and the insufficient input of potassium fertilizer and organic manure. In the rice fertilization in this area, the focus would be the balanced application of nitrogen and phosphate fertilizers, the increase of the fertilization rates of potassium fertilizer and organic manure, and the increase of top dressing, especially potassium.

[Numerical evaluation of soil quality under different conservation tillage patterns].

A 9-year field experiment was conducted on the Guanzhong Plain of Shaanxi Province to study the effects of subsoiling, rotary tillage, straw return, no-till seeding, and traditional tillage on the soil physical and chemical properties and the grain yield in a winter wheat-summer maize rotation system, and a comprehensive evaluation was made on the soil quality under these tillage patterns by the method of principal components analysis (PCA). Comparing with traditional tillage, all the conservation tillage patterns improved soil fertility quality and soil physical properties. Under conservative tillage, the activities of soil urease and alkaline phosphatase increased significantly, soil quality index increased by 19.8%-44.0%, and the grain yield of winter wheat and summer maize (expect that under no till seeding with straw covering) increased by 13%-28% and 3%-12%, respectively. Subsoiling every other year, straw-chopping combined with rotary tillage, and straw-mulching combined with subsoiling not only increased crop yield, but also improved soil quality. Based on the economic and ecological benefits, the practices of subsoiling and straw return should be promoted.

[Nitrate leaching characteristics of wheat-corn rotation farmland in Guanzhong area of Shaanxi].

By using in situ leaching device, a field experiment was conducted to study the effects of nitrogen fertilization rate and straw mulching on the nitrate leaching at 90 cm soil depth, nitrate accumulation in soil profile (0-100 cm), crop yield, and nitrogen balance of wheat-corn rotation farmland in Guanzhong area of Shaanxi. Six treatments were installed, i. e., no fertilization (N1, 0 kg x hm(-2) x a(-1)), conventional fertilization (N2, 471 kg x hm(-2) x a(-1)), recommended fertilization (N3, 330 kg x hm(-2) x a(-1)), reduced N application (N4, 165 kg x hm(-2) x a(-1)), increased N application (N5, 495 kg x hm(-2) x a(-1)), and recommended fertilization plus straw mulching (N3 + S). The nitrate leaching loss was increased with increasing N fertilization rate. Excessive N fertilization and straw mulching could easily cause nitrate leaching. In treatment N3 + S, the annual NO3(-) -N loss at 90 cm soil depth was the greatest (22.32 kg N x hm(-2)), and the NO3(-) -N loss from N fertilization was 16.44 kg N x hm(-2) x a(-1), being 158.9% higher than that in treatment N3. Nitrate mainly accumulated in 20-60 cm soil layer. When the N application rate was 330 kg N x hm(-2) x a(-1), straw mulching had less effect on the NO3(-) -N distribution in soil profile. No significant difference was observed in the crop yield among the treatments, but reduced N application (N4) tended to decrease the yield. Under our experimental condition, a fertilization rate of 150 kg N x hm(-2) x a(-1) for wheat and 180 kg N x hm(-2) x a(-1) for maize could ensure the crop production and reduce the soil nitrate leaching and accumulation.

[Atmospheric dry and wet nitrogen deposition in typical agricultural areas of North Shaanxi].

To investigate the farmland soil nitrogen input from atmospheric dry and wet deposition, a 1-year observation was conducted in the Yulin and Luochuan areas of North Shaanxi Province from June 2007 to May 2008. The total inorganic nitrogen (TIN) deposition in Yulin and Luochuan was 22.17 and 16.95 kg x hm(-2) x a(-1), among which, wet deposition accounted for 95.1% and 90.4%, while dry deposition accounted for 4.9% and 9.6%, respectively, illustrating that the nitrogen deposition in both Yulin and Luochuan was mainly come from wet deposition. In the TIN deposition, the amount of nitrate in Yulin and Luochuan was 12.22 and 9.24 kg x hm(-2) xa(-1), accounting for 55.1% and 54.5%, respectively. The amount of wet deposition and the percentage of nitrate in TIN deposition were higher in Yulin than in Luochuan, because of the differences in pollution level, weather condition, and underlying surface characteristics.

[Weed biodiversity in winter wheat field of loess soil under different fertilization regimes].

Employing an inverted 'W' investigation procedure with 9 sampling locations and adopting a biodiversity analysis approach integrated with typical statistic method, this paper studied the effects of different long-term stationary fertilization regimes on the weed biodiversity in winter wheat fields on loess soil. The results showed that in the experimental plots, there were 16 weed species belonging to 10 family and 16 genera, occupying about 34% of the total number of weed species in winter wheat fields in Shaanxi Province. The weed biodiversity was decreased with the improvement of soil nutrient status. There were 3-5 weed populations in treatments NPK and NPK plus organic materials, and 6-8 populations in treatments CK, N, NK and NP. The relative abundance of weeds ranged from 0 to 73%, and the ranges of Shannon's diversity index, Shannon's evenness index and Margalef' s species richness index were 0.2-1.08, 0.05-0.26 and 0.26-1.26, respectively. All of these 3 parameters were higher in unbalanced than in balanced fertilization treatments, and the differences between unbalanced and balanced fertilization treatments were significant in most case, which was probably due to the different status of available soil nutrients and might have different effects on the growth of weeds.