Combining rhizosphere and soil-based P management decreases the P fertilizer demand of China by more than half based on LePA model simulations

Phosphorus (P) is a finite natural resource and is increasingly considered to be a challenge for global sustainability. Agriculture in China plays a key role in global sustainable P management. Rhizosphere and soil-based P management are necessary for improving P-use efficiency and crop productivity in intensive agriculture in China. A previous study has shown that the future demand for phosphate fertilizer by China estimated by the LePA model (legacy phosphorus assessment model) can be greatly reduced by soil-based P management (the building-up and maintenance approach). The present study used the LePA model to predict the phosphate demand by China through combined rhizosphere and soil-based P management at county scale under four P fertilizer scenarios: (1) same P application rate as in 2012; (2) rate maintained same as 2012 in low-P counties or no P fertilizer applied in high-P counties until targeted soil Olsen-P (TP_Olsen) level is reached, and then rate was the same as P-removed at harvest; (3) rate in each county decreased to 1–7 kg ha^–1 yr^–1 after TP_Olsen is reached in low-P counties, then increased by 0.1–9 kg ha^–1 yr^–1 until equal to P-removal; (4) rate maintained same as 2012 in low-P counties until TP_Olsen is reached and then equaled to P-removal, while the rate in high-P counties is decreased to 1–7 kg ha^–1 yr^–1 until TP_Olsen is reached and then increased by 0.1–9 kg ha^–1 yr^–1 until equal to P-removal. Our predictions showed that the total demand for P fertilizer by whole China was 693 Mt P₂O₅ and according to scenario 4, P fertilizer could be reduced by 57.5% compared with farmer current practice, during the period 2013–2080. The model showed that rhizosphere P management led to a further 8.0% decrease in P fertilizer use compared with soil-based P management. The average soil Olsen-P level in China only needs to be maintained at 17 mg kg^–1 to achieve high crop yields. Our results provide a firm basis for government to issue-relevant policies for sustainable P management in China.     

Correlation of production constraints with the yield gap of apple cropping systems in Luochuan County,China

Apple occupies a dominant position in fruit production globally, and has become the main income source of local smallholder farmers in Luochuan County in the Loess Plateau area, one of the largest apple production areas in China. However, the annual productivity of apple orchards in this region remains low and has gradually declined over the years. The distinction and correlation of production constraints can contribute to the promotion of apple orchard productivity and the development of a sustainable orchard system. In the present study, survey data from 71 smallholder farmers were analyzed using a yield gap model to distinguish the production constraints and determine their correlation with the yield gap based on the structural equation model(SEM). The results indicated that the average apple yield in Luochuan County was 29.9 t ha~(–1) yr~(–1), while the attainable yield(Y_(att); the highest yield obtained from the on-farm surveys) was 58.1 t ha~(–1) yr~(–1). The average explained and unexplainable yield gaps were 26.3 and 1.87 t ha~(–1) yr~(–1). According to the boundary line analysis, crop load,number of sprayings and base fertilizer N were the top three constraints on apple production in 9.8, 7.8 and 7.8% of the plots, respectively. Among the production constraints, crop load and fruit weight affected apple yield through direct pathways,whereas other constraints influenced apple yield through an indirect pathway based on the SEM, explaining 51% of the yield variance by all the main production constraints. These results can improve the current understanding of production constraints and contribute to the development of management strategies and policies for improving apple yield.     

Soil Organic Carbon,Black Carbon,and Enzyme Activity Under Long-Term Fertilization

The present study aims to understand the effects of long-term fertilization on soil organic carbon (SOC), black carbon (BC), enzyme activity, and the relationships among these parameters. Paddy field was continuously fertilized over 30 yr with nine different fertilizer treatments including N, P, K, NP, NK, NPK, 2NPK (two-fold NPK), NPK+manure (NPKM), and CK (no fertilization), N, 90 kg urea-N ha⁻¹ yr⁻¹; P, 45 kg triple superphosphate-P₂O₅ ha⁻¹ yr⁻¹; K, 75 kg potassium chloride-K₂O ha⁻¹ yr⁻¹; and pig manure, 22 500 kg ha⁻¹ yr⁻¹. Soil samples were collected and determined for SOC, BC content, and enzyme activity. The results showed that the SOC in the NPKM treatment was significantly higher than those in the K, P, and CK treatments. The lowest SOC content was found in the CK treatment. SOC content was similar in the N, NP, NK, NPK, 2NPK, and NPKM treatments. There was no significant difference in BC content among different treatments. The BC-to-SOC ratios (BC/SOC) ranged from 0.50 to 0.63, suggesting that BC might originate from the same source. Regarding enzyme activity, NPK treatment had higher urease activity than NPKM treatment. The urease activity of NPKM treatment was significantly higher than that of 2NPK, NP, N, P, K, CK, and NPKM treatment which produced higher activities of acid phosphatase, catalase, and invertase than all other treatments. Our results indicated that long-term fertilization did not significantly affect BC content. Concurrent application of manure and mineral fertilizers increased SOC content and significantly enhanced soil enzyme activities. Correlation analysis showed that catalase activity was significantly associated with invertase activity, but SOC, BC, and enzyme activity levels were not significantly correlated with one another. No significant correlations were observed between BC and soil enzymes. It is unknown whether soil enzymes play a role in the decomposition of BC.     

基于RUSLE的福建省长汀县河田盆地区土壤侵蚀定量研究

以RS、GIS和RUSLE模型为主要技术,选取典型的土壤侵蚀区福建省长汀县河田盆地区为研究区,通过对模型因子的合理选择,估算了该地区1988年、1998年和2010年的土壤侵蚀量,实现土壤侵蚀状况的定量评价和动态监测.结果表明:在1988年至2010年期间,研究区土壤侵蚀状况得到明显改善,平均土壤侵蚀模数由4259.11 t·km-2·a-1下降为1280.09 t·km-2·a-1,年侵蚀量由252.42万t下降至75.87万t;中度及其以上侵蚀面积由176 km2减少至62.69 km2,微度侵蚀面积由225.85 km2增加至358.9 km2.研究结果说明近22年来针对长汀河田盆地区土壤侵蚀的治理所采取的措施是卓有成效的.长汀河田盆地区水土流失进一步重点治理的区域应集中在盆地中心及其西北部等地区的高程低于400 m、植被覆盖度为20％-50％的地区.     

Reducing nitrogen fertilization of intensive kiwifruit orchards decreases nitrate accumulation in soil without compromising crop production

Excessive nitrogen(N) fertilization of high value horticultural crops is a common problem that not only increases the cost to farmers, but also negatively affects crop growth and the environment. A three-year field experiment was conducted in an intensive kiwifruit orchard in Shaanxi Province, China to compare the effects of reduced N fertilization applied as urea(U), and controlled release urea(CRU) on the N nutrition of kiwi vines, fruit yield and quality, and nitrate-N accumulation in the soil profile. The three treatments included a conventional N application rate(CF-U, 900 kg N ha~(–1) yr~(–1) as urea), two reduced N fertilization treatments where the amount of N fertilizer applied as U and CRU was reduced by 25% in 2013 and 2014, and by 45% in 2015. The 25 and 45% reduced N treatments had no adverse effects on the N concentrations in leaves and pruning branches and the fruit yield and quality of kiwi vines. However, they significantly enhanced the partial factor productivity of applied N(PFPN) and the economic benefits, and reduced nitrate accumulation in the 0–200 cm soil profile. The same benefits of reduced N fertilization were observed for both the U and CRU treatments, but the CRU treatment had the added benefit of decreasing the loss of nitrate through leaching. We concluded that the current level of N fertilization in kiwi orchards is very excessive, and reducing the N fertilizer rate by 25–45% could not only guarantee fruit yield, but also reduce N accumulation and loss.     

Causes of maize density loss in farmers' fields in Northeast China

Increasing plant density is an effective and important way to reduce maize yield gaps in Northeast China. However, the fact is that a significant plant density gap exists between optimum plant density and actual plant density in farmers' fields.To quantify the density gap between planned planting density and final harvest plant density(HPD), we studied 60 farmers' fields on three types of soil for three crop seasons from 2015 to 2017 by measuring their plant-plant distance, actual seedlings density(ASD), final HPD and yield. We also explored the potential causes of density loss by digging the places where the seedlings were missing for two consecutive years in 2016–2017. Results show that the three-year average HPD in farmers' fields was 59 699 plants ha~(–1), which was significantly lower than the planned density, including both the machine setting density(MSD; 67 962 plants ha~(–1)) and theoretical plant density(TPD; 67 467 plants ha~(–1)). No significant difference was found in HPD between years and soil types. However, for MSD and TPD, the average value in 2015 was significantly higher than that in 2016 and 2017. No significant difference between soil types was observed. Furthermore,the results from 2016 till 2017 indicated that a lack of seeds in the soil, a failure to germinate due to low-quality seeds,and a lack of seedlings breaking out of the soil due to environmental problems explained approximately 60.88, 10.33 and 28.80% of density loss, respectively. According to our survey, 63% of farmers did not know their own TPD and HPD, and 54% of farmers did not know the density loss. Therefore, we argue that farmers' limited knowledge of density and density loss is an urgent problem that needs to be solved in maize production. These observations will be useful for determining best management practices for maize production and for providing helpful suggestions for machine improvement.     

Abundance and Community Composition of Ammonia-Oxidizers in Paddy Soil at Different Nitrogen Fertilizer Rates

Ammonia oxidation, the first and rate-limiting step of nitrification, is carried out by both ammonia-oxidizing bacteria （AOB） and ammonia-oxidizing archaea （AOA）. However, the relative importance of AOB and AOA to nitrification in terrestrial ecosystems is not well understood. The aim of this study was to investigate the effect of the nitrogen input amount on abundance and community composition of AOB and AOA in red paddy soil. Soil samples of 10-20 cm （root layer soil） and 0-5 cm （surface soil） depths were taken from a red paddy. Rice in the paddy was fertilized with different rates of N as urea of N1 （75 kg N ha＂ yr-1）, N2 （150 kg N ha~ yrl）, N3 （225 kg N ha1 yrl） and CK （without fertilizers） in 2009, 2010 and 2011. Abundance and community composition of ammonia oxidizers was analyzed by real-time PCR and denaturing gradient gel electrophoresis （DGGE） based on amoA （the unit A of ammonia monooxygenase） gene. Archaeal amoA copies in N3 and N2 were significantly （P〈0.05） higher than those in CK and N1 in root layer soil or in surface soil under tillering and heading stages of rice, while the enhancement in bacterial amoA gene copies with increasing of N fertilizer rates only took on in root layer soil. N availability and soil NO3--N content increased but soil NH4＋-N content didn＇t change with increasing of N fertilizer rates. Otherwise, the copy numbers of archaeal amoA gene were higher （P〈0.05） than those of bacterial amoA gene in root lary soil or in surface soil. Redundancy discriminate analysis based on DGGE bands showed that there were no obvious differs in composition of AOA or AOB communities in the field among different N fertilizer rates. Results of this study suggested that the abundance of ammonia-oxidizers had active response to N fertilizer rates and the response of AOA was more obvious than that of AOB. Similarity in the community composition of AOA or AOB among different N fertilizer rates indicate that the community composition of ammonia-oxidizers was relatively stable in the paddy soil at least in short term for three years.     

Emission and Fixation of CO2 from Soil System as Influenced by Long-Term Application of Organic Manure in Paddy Soils

The observations of 25-yr long-term experiment in Zhejiang paddy soils showed that the soil organic matter could increase continuously with applying organic manure, and the increase in rate enhanced along with the application rates of organic manure. By mathematical modeling, the soil organic matter increased by 22 kg when 1 t of fresh FYM was applied. The CO2 emission resulting from the mineralization of soil organic matter increased with the increase in the application rate of the organic manure as well as the increase in the root residues. It is expected that the CO2 emission will be at 10.04-21.61 t ha^-1 yr^-1 when 16.5-49.5 t ha ^-1 yr^-1 of fresh FYM is applied. The soil organic carbon from mineralization and release of applied organic carbon （fresh FYM and root residues） will affect the CO2 concentration in the atmosphere. So, the higher the application rate of organic manure, the more is the fixed organic carbon. The CO2 fixation will be at 1.885-3.463 t ha^-1 yr^-1 when 16.5-49.5 t ha^-1 yr^-1 of fresh FYM is applied. Thus, the CO2 fixation will increase by 46.7 kg by applying 1 t fresh FYM. To apply organic manure continuously in rice fields may reduce the contribution to the increase of CO2 concentration in the atmosphere.     

Significant reduction of ammonia emissions while increasing crop yields using the 4R nutrient stewardship in an intensive cropping system

Ammonia (NH₃) emissions should be mitigated to improve environmental quality.Croplands are one of the largest NH₃sources,they must be managed properly to reduce their emissions while achieving the target yields.Herein,we report the NH₃ emissions,crop yield and changes in soil fertility in a long-term trial with various fertilization regimes,to explore whether NH₃ emissions can be significantly reduced using the 4R nutrient stewardship (4Rs),and its int...     

Trends of Yield and Soil Fertility in a Long-Term Wheat-Maize System

The sustainability of the wheat-maize rotation is important to China＇s food security. Intensive cropping without recycling crop residues or other organic inputs results in the loss of soil organic matter （SOM） and nutrients, and is assumed to be non- sustainable. We evaluated the effects of nine different treatments on yields, nitrogen use efficiency, P and K balances, and soil fertility in a wheat-maize rotation system （1991-2010） on silt clay loam in Shaanxi, China. The treatments involved the application of recommended dose of nitrogen （N）, nitrogen and phosphorus （NP）, nitrogen and potassium （NK）, phosphorus and potassium （PK）, combined NPK, wheat or maize straw （S） with NPK （SNPK）, or dairy manure （M） with NPK （M1NPK and M2NPK）, along with an un-treated control treatment （CK）. The mean yields of wheat and maize ranged from 992 and 2 235 kg ha-1 under CK to 5 962 and 6 894 kg ha-1 under M2NPK treatment, respectively. Treatments in which either N or P was omitted （N, NK and PK） gave significantly lower crop yields than those in which both were applied. The crop yields obtained under NP, NPK and SNPK treatments were statistically identical, as were those obtained under SNPK and MNPK. However, M2NPK gave a significant higher wheat yield than NP, and MNPK gave significant higher maize yield than both NP and NPK. Wheat yields increased significantly （by 86 to 155 kg ha-1 yr-1） in treatments where NP was applied, but maize yields did not. In general, the nitrogen use efficiency of wheat was the highest under the NP and NPK treatments; for maize, it was the highest under MNPK treatment. The P balance was highly positive under MNPK treatment, increasing by 136 to 213 kg ha-1 annually. While the K balance was negative in most treatments, ranging from 31 to 217 kg ha^-1 yr^-1, levels of soil available K remained unchanged or increased over the 20 yr. SOM levels increased significantly in all treatments. Overall, the results indicated that combinations of organic manure and inorganic nitrogen, or retuming straw with NP is likely to improve soil fertility, increasing the yields achievable with wheat-maize system in a way which is environmentally and agronomically beneficial on the tested soil.     

Soil tillage methods by years interaction for dry matter of plant yield of maize (Zea mays L.) using additive main effects and multiplicative interaction model

The objective of this study was to assess soil tillage methods by years interaction for dry matter of plant yield of maize(Zea mays L.) grown in West Poland by the additive main effects and multiplicative interaction model. The study comprised four soil tillage methods, analysed in 12 years through field trials arranged in a randomized complete block design, with four replicates. Dry matter of plant yield of the tested soil tillage methods varied from 86.7 dt ha~(–1)(for no-plough tillage in 2005) to 246.4 dt ha~(–1)(for complete conventional tillage in 2012), with an average of 146.6 dt ha~(–1). In the variance analysis, 49.07% of the total dry matter of plant yield variation was explained by years, 12.69% by differences between soil tillage methods, and 10.53% by soil tillage methods by years interaction. Dry matter of plant yield is highly influenced by soil tillage methods by years factors.     

旅游干扰下的天山北坡水蚀经济损失评估——以西白杨沟流域山地景区为例

为探讨旅游干扰下山地景区水蚀强度和经济损失变化规律,以水蚀典型区——西白杨沟流域山地景区为案例地,基于样地调查数据,采用中国土壤流失方程（Chinese soil loss equation,CSLE）与水蚀经济损失评估模型,定量估算不同旅游干扰强度下水蚀经济损失,分析西白杨沟景区水蚀经济损失变化规律及其与土壤理化性质、植被覆盖度的关系。结果表明：不同旅游干扰强度下土壤理化性质、植被覆盖度差异显著。与对照组相比,重度干扰区土壤含水量、饱和含水量及土壤孔隙度的降幅分别为51.67%、32.23%、13.30%;土壤碱解氮、有效磷及有机质含量均随干扰强度增加呈下降趋势,而速效钾含量却趋于增加;与对照组相比,轻度、中度、重度干扰区植被覆盖度分别下降14.18%、43.32%、92.35%。随旅游干扰强度的增加,土壤可蚀性K值与生物措施B值明显增加,土壤侵蚀量呈显著增长趋势（P<0.05）,与轻度干扰区相比,中度、重度干扰区土壤侵蚀模数增幅分别为79.31%、204.79%。场内经济损失、场外经济损失及水蚀经济总损失随干扰强度的增加呈上升趋势,其中场内经济损失远大于场外经济损失,土壤养分损失及植被多样性损失作为水蚀经济总损失的主要部分,二者在轻度、中度、重度干扰区分别占水蚀经济总损失的93.56%、92.68%、94.94%,且干扰强度为中度、重度时,植被多样性损失高于土壤养分损失,分别达1.17×10⁴元·hm^-2·a^-1和2.49×10⁴元·hm^-2·a^-1。植被覆盖度对水蚀经济损失响应最为敏感,植被覆盖度每减少1%,水蚀经济损失增加4.98×10⁴元。研究表明,旅游干扰强度是影响山地景区水蚀强度和经济损失的关键因素,为此应结合土壤侵蚀参数分析,加强山地景区土体裸露化管理,种植耐践踏植被,核算旅游容量,控制旅游干扰强度。     

暴雨条件下紫色土区玉米季坡耕地氮素流失特征

【目的】研究暴雨条件下,川中丘陵紫色土区坡耕地玉米全生育期土壤侵蚀及氮素流失规律,为研究区氮素流失预测和有效防控提供科学依据。【方法】采用人工模拟降雨与径流小区相结合的方法,在玉米苗期（5月1日）,拔节期（5月26日）,抽雄期（6月27日）和成熟期（8月4日）进行模拟降雨,结合川中丘陵紫色土区夏季暴雨多的特点,开展降雨强度为1.5 mm·min^-1,坡度为15°条件下地表径流、壤中流和侵蚀泥沙中氮素流失特征的研究。【结果】（1）玉米各生育时期地表径流产流率和产沙率总体表现为随降雨时间延长而呈增加的变化趋势,地表径流产流率和产沙率均表现苗期最高,抽雄期最低;壤中流产流率则表现为抽雄期最高,成熟期最低。（2）玉米各生育时期地表径流中总氮流失率随降雨时间延长而呈增加,在降雨36 min后基本趋于稳定,总氮和可溶性总氮流失率均在玉米苗期最大,平均值分别为5.24和4.74 mg·m^-2·min^-1;玉米全生育期地表径流中硝态氮流失率则在降雨30 min后基本稳定,铵态氮流失率呈现波动性,硝态氮和铵态氮流失率均在玉米拔节期最大,平均值分别为3.90和0.14 mg·m^-2·min^-1。在玉米全生育期地表径流中总氮,可溶性总氮和硝态氮流失量与地表径流量呈现极显著线性关系。（3）壤中流中总氮流失率在玉米各生育时期随降雨时间延长缓慢增加,壤中流中可溶性总氮和硝态氮流失率在玉米苗期、拔节期和成熟期变化趋势与总氮一致,而铵态氮流失率在玉米全生育期呈现波动性;总氮,可溶性总氮,硝态氮和铵态氮流失率均在玉米拔节期最大,平均值分别为25.04、20.34、16.20和0.22 mg·m^-2·min^-1。在玉米全生育期壤中流中总氮,可溶性总氮和硝态氮流失量与壤中流量呈现显著线性关系,且均在玉米拔节期表现为斜率最大。（4）玉米各生育时期侵蚀泥沙中氮素流失率均随降雨时间延长而增加,但在玉米苗期表现为增幅最大,平均值为0.92 mg·m^-2·min^-1。在玉米全生育期,侵蚀泥沙中氮素流失量与侵蚀泥沙量呈现极显著线性关系。（5）地表径流中不同形态氮素流失量均在玉米苗期和拔节期最大,壤中流中总氮流失量则在玉米拔节期和抽雄期最大,侵蚀泥沙中氮素流失量在玉米苗期最大。壤中流为研究区坡耕地氮素流失的主要途径,占氮素流失总量的64.07%-83.39%。可溶性总氮为径流中氮素流失主要形态,以硝态氮为主要形态。【结论】1.5 mm·min^-1降雨强度下,地表径流和壤中流中总氮流失量分别在玉米苗期和拔节期最高,可溶性总氮和硝态氮流失量均在拔节期最高,存在水体富营养化潜在风险,控制苗期地表径流量和拔节期壤中流量可减少该区域氮素流失量。     

Changes in soil organic carbon pools following long-term fertilization under a rain-fed cropping system in the Loess Plateau,China

Understanding the mechanism of soil organic carbon(SOC) sequestration is of paramount importance in sustaining crop productivity and mitigating climate change. Long-term trials were employed to investigate the responses of total SOC and its pools, i.e., mineral-associated OC(MOC), particulate OC(POC, containing Light-POC and Heavy-POC), to fertilization regimes at Yangling(25-year), Tianshui(35-year) and Pingliang(37-year) under a rain-fed cropping system in the Loess Plateau. The fertilization regimes in each trial included three treatments, i.e., control(no nutrient input, CK), chemical fertilizers(CF), and organic manure plus chemical fertilizers(MCF). Relative to the CK, long-term fertilization appreciably increased SOC storage by 134, 89 and 129 kg ha~(–1) yr~(–1) under CF, and 418, 153 and 384 kg ha~(–1) yr~(–1) under MCF in plough layer soils(0–20 cm), respectively, at the Yangling, Tianshui and Pingliang sites. The MOC pools accounted for 72, 67 and 64% of the total SOC at the above three sites with sequestration rates of 76, 57 and 83 kg ha~(–1) yr~(–1) under CF and 238, 118 and 156 kg ha~(–1) yr~(–1) under MCF, respectively. Moreover, the MOC pool displayed a saturation behavior under MCF conditions. The POC accordingly constituted 27, 33 and 36% of SOC, of which Light-POC accounted for 11, 17 and 22% and Heavy-POC for 17, 16 and 15% of SOC, respectively. The sequestration rates of POC were 58, 32 and 46 kg ha~(–1) yr~(–1) under CF, and 181, 90 and 228 kg ha~(–1) yr~(–1) under MCF at the three respective sites, in which Light-POC explained 59, 81 and 72% of POC under CF, and 60, 40 and 69% of POC under MCF, with Heavy-POC accounting for the balance. Compared with CK, the application of CF alone did not affect the proportions of MOC or total POC to SOC, whereas MCF application markedly reduced the proportion of MOC and increased the POC ratio, mainly in the Light-POC pool. The distribution of SOC among different pools was closely related to the distribution and stability of aggregates. The present study confirmed that organic manure amendment not only sequestered more SOC but also significantly altered the composition of SOC, thus improving SOC quality, which is possibly related to the SOC saturation level.     

The potential of green manure to increase soil carbon sequestration and reduce the yield-scaled carbon footprint of rice production in southern China

Green manure (GM) has been used to support rice production in southern China for thousands of years. However, the effects of GM on soil carbon sequestration (CS) and the carbon footprint (CF) at a regional scale remain unclear. Therefore, we combined the datasets from long-term multisite experiments with a meta-analysis approach to quantify the potential of GM to increase the CS and reduce the CF of paddy soils in southern China. Compared with the fallow–rice practice, the GM–rice practice increased the soil C stock at a rate of 1.62 Mg CO₂-eq ha^–1 yr^–1 and reduced chemical N application by 40% with no loss in the rice yield. The total CF varied from 7.51 to 13.66 Mg CO₂-eq ha^–1 yr^–1 and was dominated by CH₄ emissions (60.7–81.3%). GM decreased the indirect CF by 31.4% but increased the direct CH₄ emissions by 19.6%. In the low and high CH₄ emission scenarios, the CH₄ emission factors of GM (EF_gc) were 5.58 and 21.31%, respectively. The greater soil CS offset the increase in GM-derived CF in the low CH₄ scenario, but it could not offset the CF increase in the high CH₄ scenario. A trade-off analysis also showed that GM can simultaneously increase the CS and reduce the total CF of the rice production system when the EF_gc was less than 9.20%. The variation in EF_gc was mainly regulated by the GM application rates and water management patterns. Determining the appropriate GM application rate and drainage pattern warrant further investigation to optimize the potential of the GM–rice system to increase the CS and reduce the total CF in China.     

Sensing soil and foliar phosphorus fluorescence in <Emphasis Type="Italic">Zea mays</Emphasis> in response to large phosphorus additions

Additions of large loads of phosphorus (P) enriched animal manure to soils and the persistence of their environmental impact have been associated with continued water quality impairment in regions of high density of confined animal feeding operations. Foliar P in corn (Zea mays L.) and changes in labile P in Aquic Hapludults were determined following P application of 0–560 kg P ha^?1 as KH₂PO₄ and an application of Fe³⁺ (150 mg Fe³⁺ kg^?1) in field mini-lysimeters to develop calibrations of soil and plant nutritional responses. X-ray fluorescence (XRF) scanning of uppermost leaves of plants at the V2, V5, and V8 stages showed that foliar P proportionally increased with addition rates. Exchangeable and enzyme-labile P forms were effective indicators of foliar XRFS-P for up to 30 days after emergence. Phosphorus calibration curves developed for flag leaves showed that spatial distribution of foliar P (3.6, 4.2, and 5.3 g kg^?1) corresponded to field zones treated with 0, 15, and 30 kg P ha^?1 as dairy manure P for the past 18 years. Up-to-date crop uptake and availability of P in these Hapludults were best described by a square root function of soil XRFS-P and total exchangeable inorganic P (r² = 0.4; RMSE = 419 and 422 g ha^?1, respectively). Therefore, a timely knowledge of canopy P status and its linkage to actual soil P status supports in situ element-specific sensing and precision nutrient management in order to manage the declining use-efficiency in crops and reduce potential loss to the environment.     

Probability of profitable yield response to nitrification inhibitor used with liquid swine manure on corn

Nitrification inhibitors (NI) can be used with liquid swine manure (LSM) to decrease potential NO₃ losses, but knowledge specifying when and where NI can increase corn (Zea mays L.) yields is limited. Eleven on-farm evaluation trials (OET) were conducted in 2009 and 15 in 2010 to identify site-specific factors for using Instinct (an encapsulated form of nitrapyrin) with LSM in Iowa. Farmers injected LSM in the fall in at least three field-long strips with and without NI. Yield responses (YR) to NI were calculated by dividing yield monitor data into 50-m cells within each field. Hierarchical models were used to estimate predictive probabilities of profitable YR for two categories of monthly average rainfall and soil drainage. On average, NI produced no YR in relatively normal 2009 and a 0.15 Mg ha^?1 YR in extremely wet 2010. The NI did not change late-season corn N status but half of corn stalk nitrate test (CSNT) samples were N deficient in 2009 and about 65 % in 2010. Fields receiving >90 cm March through August rainfall in 2010 were predicted 65 % more likely to have economic YR (>0.13 Mg ha^?1) than fields receiving <90 cm rainfall. Within-field variability in YR was about four times greater than among-field variability, but within field-level factors had no significant effects on YR. The NI effects may not have lasted long enough to increase yields across all OET and predictive probabilities suggest that NI may produce profitable YR only when spring and summer rainfall exceed the long-term averages by more than 40 %.     

炼山对杉木人工林生态系统的影响 Ⅰ炼山初期林地水土流失的初步研究

本文采用径流小区定位观测法分析研究炼山与不炼山的水土流失差异。通过一年的研究结果表明:炼山后第一年水、土、肥流失十分严重,炼山的年径流量为2743.49m~3/ha,年土壤流失量为24.811T/ha,分别是不炼山的11倍和88倍。大量水土流失伴随着养分流失。有机质、速效氮、磷和钾的流失量分别为不炼山的15倍、24倍、16倍和5倍。经回归分析、炼山因素在影响本区水土流失诸因子中占主导地位。在本试验条件下24°—32°可能是水流面蚀强度的临界坡度。     

基于GIS和USLE的宁乡市土壤侵蚀定量评价

以遥感影像数据、DEM数据、降雨数据、土壤类型数据为基础,通过GIS和RS技术,结合美国通用水土流失方程(USLE)估算宁乡市的土壤侵蚀模数,模型指标包括降雨侵蚀力因子(R)、土壤可侵蚀性因子(K)、坡度坡长因子(LS)、植被覆盖度因子(C)、水土保持措施因子(P)。评价结果表明,2015年宁乡市土壤平均侵蚀模数为1 410.64t/(km2·年),属于中度侵蚀等级状情况,土壤侵蚀类型主要为微度侵蚀、剧烈侵蚀和轻度侵蚀,侵蚀面积分别为1 548.87、434.16和397.91km2,占侵蚀总面积的53.84%、15.09%和13.88%。土壤侵蚀模数较高的地区主要集中在宁乡市的沩山、长冲等山地、丘陵地区。系统分析出宁乡市土壤侵蚀与USLE模型的相关影响因子的关系,海拔高程与土壤侵蚀强度成正相关关系,与侵蚀面积成负相关关系,在200m海拔高程地区微度侵蚀面积范围最大。县内土壤侵蚀面积最大地区是在25°以下的坡度带,土壤侵蚀面积总体随着坡度的增加而减小。土地利用类型中耕地和林地的土壤侵蚀最为严重,其次是城镇用地草地水域裸地。根据宁乡市土壤侵蚀现状,提出综合治理措施,以期为政府开展水土保持工作提供科学依据。