Modelling stochastic crop response to fertilisation when carry-over matters

Soils in a large part of Niger's agricultural area are sandy and very low in nitrogen (N), phosphorus (P) and organic matter. This low soil fertility combined with low and erratic rainfall constitutes a severe constraint on food cropping in the area. Although agronomists have advised chemical fertilization as a means of improving soil fertility, little fertilizer has been used in this area of the world. The economic management of soil fertility in the agricultural area of Niger is analyzed using a dynamic model of farmer decision-making under uncertainty. The model is based on agronomic principles of plant growth and accounts for the carry over of P, an immobile nutrient. At current input prices, a soil P content of at least 14 ppm is found to be desirable. This target is above the natural soil fertility level of about 3 ppm. It can be maintained with a moderate annual application (12 kg P₂O₅ ha^?1) of simple superphosphate. Results also suggests that returns to N fertilization are too low and variable to warrant the use of this input.     

The effects of repeated soil wetting and drying on lowland rice yield with system of Rice Intensification (SRI) methods

In lowland rice farming, water management is the most important practice that determines the productivity of other inputs, e.g. nutrients, herbicides, pesticides, farm machinery, microbial activity, mineralization rates. Deliberate flooding or poor drainage that keeps soil saturated is detrimental to crops and degrades soil quality. This study evaluated whether rice grain yield could be increased relative to continuous flooding by using the management practices of the System of Rice Intensification (SRI). The effects of SRI's repeated wetting and drying cycles plus different plant populations were investigated at Sapu Research Station in The Gambia, on an alluvial soil between 2000 and 2002. The water management practices proposed for SRI were found to be beneficial to rice growth. At 20 cm spacing, average grain yield with SRI practice was 7.3 t ha^?1 compared with 2.5 t ha^?1 under continuous flooding. At 30 cm spacing SRI practice yielded 6.6 t ha^?1, while under continuous flooding, grain yield was only 1.7 t ha^?1. Even wider spacing did not produce higher yield. At 40 cm spacing, SRI management gave 4.7 t ha^?1, while continuous flooding yielded 1.3 t ha^?1. Thus overall, SRI practices gave better results than continuous flooding. This was probably as a result of increased nutrient availability and superior growing conditions which enhanced physiological development and grain yield. Rewetting dry soil reportedly facilitates nitrogen mineralization. The phenomenon of having a flush of nitrogen mineralization occurring after rewetting dry soil was first reported by Birch in 1958. This intensive pathway of nitrogen mineralization and nitrogen availability has potential to increase lowland rice yields in ways consistent with sustainable agricultural production.     

REDUCING THE NITROGEN INPUT ON ARABLE FARMS

Nitrogen response curves derived from experimental data are used with a profit maximising condition to obtain optimum N rates, yields and gross margin losses for a range of nitrogen and cereal prices. These results are used with a linear programming model of an arable farm to estimate changes in the optimal cropping allocation and hence the farm scale effects of relative price changes. Total nitrogen applied is found to have a limited response: a doubling of the N price reduces the total used by between 24% and 10% depending on the availability of low-N break-crops. Cereal price changes reduce profitability severely before having any significant effect on N use.     

河北省不同利用方式农田土壤氮磷环境风险分析

弄清不同利用方式农田土壤氮磷养分平衡状况,进而明确其环境风险特征,为进一步指导土壤养分管理及环境政策制定具有重要意义。研究以河北省的粮田、果园和菜地为研究对象,通过分析三种利用方式氮磷的输入、化肥和有机肥的分配比例及氮磷养分的盈余状况,并结合化肥使用环境风险指数,评价三种不同利用方式化肥氮磷的环境风险类型。结果表明,氮总输入量为菜地明显高于果园和粮田,磷总输入量为菜地和果园明显高于粮田,且粮田和菜地氮磷输入主要以化肥为主。三种不同利用方式农田氮磷均呈盈余状态,其中氮盈余率为果园(532.6%)明显高于菜地(61.5%)和粮田(31.6%),磷盈余率为菜地(700.4%)和果园(615.7%)明显高于粮田(66.6%)。化肥氮磷的环境风险指数均为菜地(0.83)明显高于粮田(0.59-0.62),三种不同利用方式下化肥氮磷的环境风险类型均达低度风险及以上,特别是菜地达严重风险。为了农业的可持续发展,河北省粮田应控制氮磷肥的投入,果园和菜地应加大减少氮磷肥化肥投入,以减少对环境的潜在危害。同时为了更好地培肥地力,在控制施肥总量的前提下应加大粮田和菜地有机肥的投入比例。     

Managing phosphorous soil dynamics over space and time

Understanding the relationship between soil fertility dynamics and crop response is conceptually appealing. Even more appealing is comprehension of the spatial and temporal heterogeneity of these connections over a production surface and across seasons. But gaining knowledge about these interactions is difficult because nutrient carryover dynamics and crop response to inputs are determined simultaneously on the one hand, and sequentially on the other. A second problem enters when crops are rotated, for example, the corn [Zea mays (L.) Merr.]–soybean [Glycine max (L.) Merr.] system commonly practiced in the U.S. Corn Belt. This article examines nutrient carryover–crop response dynamics using data from a corn‐soybean, variable rate nitrogen (N), and phosphorous (P) experiment conducted over five years in Minnesota, USA. Site‐specific corn response to N and P and soybean response to P is estimated with a P carryover equation. Estimates are used in a dynamic programming model to determine site‐specific optimal N and P fertilizer policies, soil P evolution, and profitability. The net present value of managing N and P site‐specifically is compared to a strategy in which these inputs are managed uniformly following Extension guidelines. The results suggest that when P carryover is accounted for in determining optimal P fertilizer rates, returns to the variable rate strategies are higher than returns to a uniform or whole‐field management strategy.     

Nitrate pollution control under soil heterogeneity

This article presents results on measures to abate nitrogen pollution when soil heterogeneity is considered by using a dynamic model of corn production. Several policy options for the control of nitrate pollution are evaluated by their cost efficiency. While results show that a nitrogen standard or tax is a good second-best control instrument, neglecting dynamics may lead to the wrong choice of instrument. Other important findings for the design of nonpoint pollution policy measures are that water pricing, as advocated by the Water Framework Directive, is inefficient as a pollution abatement tool, and differentiating control measures by soil type enhances welfare, although welfare gains may be small.     

氮肥减量及秸秆替代过量氮肥下冬小麦/夏玉米轮作体系氮素淋失风险研究

针对过量施用氮肥和地下水硝酸盐超标的现状,探索减量施氮、秸秆替代过量氮肥下土壤氮素的淋失风险,以期为降低氮素淋失风险提供科学依据。通过在河北省徐水县进行连续4年的冬小麦—夏玉米轮作体系田间定位试验,分析耕作(少耕和常规耕作)、施氮量(无机氮0、200和300 kg/hm~2)和秸秆(还田、不还田)等措施对作物收获后土壤无机氮累积、土壤—作物体系氮平衡状况以及冬小麦和夏玉米产量的影响。结果表明,小麦收获后,过量施氮处理0~100 cm土壤硝态氮累积量显著高于其它处理,高达221 kg/hm~2,过高的土壤残留硝态氮增加玉米高温多雨季氮素淋洗风险。3年氮平衡累积量比较显示,过量施氮、少耕/常规耕作减量施氮秸秆还田3处理的氮平衡值无显著性差异,以少耕减量施氮秸秆还田最低,为236 kg/hm~2,过量施氮处理最高,为281 kg/hm~2,三者均显著高于少耕/常规耕作减量施氮秸秆不还田处理。冬小麦—夏玉米轮作体系氮平衡值与0~100 cm土层的土壤无机氮、土壤硝态氮累积量呈显著正相关,说明氮素大量盈余会导致0~100 cm土壤剖面无机氮大量累积,尤其是硝态氮大量累积。少耕和常规耕作减量施氮秸秆还田处理的冬小麦、夏玉米产量与过量施氮无显著差异。综合考虑土壤无机氮累积量、氮平衡值和作物产量,少耕或者常规耕作下,可以利用秸秆氮替代过量无机氮,降低氮素淋洗风险。     

Agronomic considerations for urban agriculture in southern cities

Urban and peri-urban agriculture (UA) provide a significant contribution to the total food requirements of cities, especially in southern cities of the developing world. Increasing food production in UA is therefore a necessity for increasing the food security of the urban poor. Urban environments are inherently different from rural environments and these differences in environmental conditions are expected to impact differently on crop growth. This review describes agronomic issues that are unique to UA and identifies possible interventions to address them. The constraints that can significantly differ include temperature, air quality, solar radiation and climate. The growth-limiting and growth-reducing factors that affect actual production in UA include water availability, nutrient supply, soil degradation, pests and soil pollution. The interventions addressing these constraints require action at both field level, and municipal or regional levels. The food security of the urban poor will therefore require coordinated efforts and cooperation between the farmers who produce food and the planners and policy makers who manage the supporting systems such as markets, inputs and land registration.     

东北黑土区设施栽培对土壤养分的影响——以哈尔滨地区为例

设施蔬菜土壤养分是制约蔬菜生长及品质的关键因子,迄今有关东北黑土区设施栽培对土壤养分的影响的研究鲜见报道。本研究以哈尔滨市为研究区,通过调查取样,分析了黑土区设施蔬菜栽培土壤的碱解氮、速效磷、速效钾、有机质和pH的丰缺程度,比较了设施蔬菜土壤与露天蔬菜土壤的养分含量。结果表明:(1)设施蔬菜土壤的碱解氮含量处于亏缺状态,其他土壤养分含量均处于高水平状态。(2)哈尔滨市设施蔬菜土壤养分含量均较露地蔬菜土壤高。碱解氮、速效磷和速效钾含量起初随着设施使用年限的增加而增加,到第8年达到最大值,随后开始降低。土壤有机质的含量到第8年达到最大值,随后开始降低。土壤pH随设施使用年限的增加起初变化不大,到第8年明显降低,达到最低值,之后又有所上升。(3)哈尔滨市区内的设施蔬菜土壤速效磷含量高,外县的设施蔬菜土壤碱解氮、速效钾和有机质含量高,郊区的设施蔬菜土壤碱解氮、速效磷、速效钾及有机质的含量均最低。本项研究表明,设施栽培使哈尔滨地区土壤速效养分及有机质含量发生明显变化,且随着地区不同而差异明显,土壤养分含量随设施使用年限而变化,使用8年的设施菜地土壤中pH值最低,碱解氮、速效磷、速效钾及有机质含量最高。     

辽宁棕壤耕地质量评价及障碍因素类型分区研究

[目的]以土壤类型为基础,选取土壤管理、理化性质、土壤养分、剖面性状、立地条件和气候条件等6个方面14个指标对辽宁棕壤耕地质量进行综合评价,在分析主要障碍因素基础上,根据障碍因素组合类型的不同对辽宁棕壤耕地进行质量障碍因素类型分区。[方法]采用模糊数学法和层次分析法,利用障碍度模型对辽宁棕壤耕地质量障碍因素进行诊断,分析棕壤耕地质量障碍因素类型分区。[结果](1)辽宁棕壤耕地高等地、中等地和低等地,分别占棕壤耕地总面积的21.49%、59.18%和19.33%,耕地质量等级以中等地为主;(2)障碍因素组合类型共14种,根据障碍因素不同划分为3个耕地质量障碍因素类型区,即有机质障碍类型区、灌溉能力障碍类型区、质地障碍类型区,分别占棕壤耕地总面积的86.45%、10.75%和2.80%。[结论](1)针对障碍因素类型分区,提出各区以障碍因素为主的耕地质量保护与提升措施,从而保证粮食生产;(2)文章从耕地土壤类型角度研究耕地质量障碍因素类型分区及其利用策略,为耕地质量保护与提升研究提供新视角,为耕地资源分区利用与管护研究提供参考依据。     

AGGREGATE DEMAND FOR NITROGENOUS FERTILISER IN THE UNITED KINGDOM: ANOTHER LOOK*

Economic theory must be subjected to continuous empirical testing and verification. Consequently any econometric model proposed may be re-tested and modified in the light of imporved data availability and additional observations generated by the real world. This paper re-examines U.D. aggregate demand for nitrogen: after otaining a meaningful data series for the price of nitrogen it is found that earlier functions fitted do not now stand up to the passage of time. Alternarte hypotheses are then put forward.     

华北平原小麦—玉米轮作对奶牛粪肥的消纳能力研究

奶牛粪便富含植物营养物质,制作粪肥还田对提高土壤养分、改善土壤质量、提高作物产量以及解决牛场环境污染均具有重要的意义。文章设计了空白(CK)、习惯施肥(NPK)和不同粪肥量M30、M60、M120、M240处理,开展不同施肥模式对小麦玉米产量、土壤肥力及硝态氮残留等方面的研究。研究结果表明,连续施用两年粪肥后,粪肥施用量较高的M120、M240处理小麦玉米籽粒产量、秸秆产量、土壤全氮和速效钾含量均高于NPK处理;施用粪肥均提高土壤有机质和速效磷的含量。施用粪肥与常规施肥相比,在0~200cm的土壤剖面上NO~-_3-N分布特征完全不同,施用粪肥各处理土壤NO~-_3-N除在耕层含量较高外,耕层以下含量均较低,且差异较小。0~200cm土壤剖面NO~-_3-N累积量随着粪肥的增加而增加,6月份0~200cm粪肥各处理NO~-_3-N累积量均低于NPK处理,10月份NO~-_3-N累积量M240处理高于NPK处理,表现出过量施用粪肥造成NO~-_3-N大量累积。     

基于非点源污染的密云水源保护区水环境容量核算及其分配

根据密云水库一级保护区内河流、水文、污染物特征,采用输出系数法模型进行研究区非点源污染负荷估算,并以COD、氨氮和总磷为控制因子,建立一维河流水质模型,定量计算研究区水环境容量,在此基础上,对研究区水环境剩余容量及污染排放削减量进行分配。结果表明:研究区非点源污染负荷输出总值分别COD433.84t/a、氨氮47.14t/a和总磷40.75t/a,4种非点源污染类型中畜禽养殖的COD、氨氮和总磷分别占各项总污染负荷的78.6%、60%、87.1%,成为保护区内主要的污染来源,水土流失污染、农村生活污水依次之,民俗旅游的污染负荷贡献率最低;污染源类型中,生活和民俗旅游污水则主要造成COD污染,而水土流失主要引起氨氮和总磷污染。保护区内COD、氨氮和总磷的水环境容量分别为3 170.36t/a、128.20t/a、25.27t/a,相较于污染负荷,水环境容量偏小。其中,总磷的污染风险最大,其环境剩余容量达到负值,应对其进行总量15.48t/a的削减。秉承公平和效益原则,总磷排放量削减分配中,畜禽养殖、生活污水、民俗旅游、水土流失各污染源的削减比例分别为44.26%、10.83%、40.90%、6.15%;氨氮的水环境剩余容量分配中,畜牧养殖的分配量最小、分配比例最低(14.16t、49.85%);畜牧养殖成为研究区内重点削减和控制的污染源。基于非点源污染的水环境容量计算及其分配研究可为保护区水环境控制管理与污染防治提供科学依据与决策支持。对加强密云水库饮水源保护,控制上游污染源,保证水质安全,确保北京市民人体健康和经济发展具有重要意义。     

Effect of land-use change on soil fertility characteristics within water-stable aggregates of two cultivated soils in northern Iran

Forest and pastureland soils in highland of northern Iran are being seriously degraded and destructed due to extensive agricultural activities. These land use changes are usually accompanied by decreasing in concentrations of soil organic carbon and nutrients and also deterioration of soil structure in these regions. However, studies on concentration of nutrients and carbohydrates in soils suggest that the location of nutrients within aggregates of each size should be determined. This study was to evaluate the nutrient elements and carbohydrate distributions within water-stable aggregates (WSA) of virgin forest and pasture lands under different land uses in Alborz maintain range, northern Iran. In September 2006, soil samples were collected from depths of 0–20 cm in Typic Haploxerolls soils. The overall pattern indicated that the mean weight diameter (MWD) and WSA were greater in the virgin pasture and forest soils compared with the adjacent cultivated (ex-forest and ex-pasture) soils and aggregates of >1.0 mm size were dominant in the virgin soils, whereas the cultivated soils comprised aggregates of the size ≤0.5 mm. Distribution of organic carbon, nitrogen, phosphorus and carbohydrates within the WSA showed preferential enrichment of these parameters in the macroaggregate fraction (4.75–1.0 mm) for the virgin soils and microaggregate fraction (>0.25 mm) for the exposed soils. Cultivation decreased the concentration of carbohydrates by 23.6% and 20.6% in ex-forest and ex-pasture lands, respectively. Average distribution of total exchangeable bases within WSA showed that the cultivation of forest and pasture soils significantly led to reduce in these nutrient in the 4.75–2.0 mm fraction and increase in concentration of these exchangeable cations in <0.25 mm fractions. In general, results indicated that cultivation significantly led to 71% and 6% reductions in total exchangeable bases within the 4.75–2.0 and <0.25 mm aggregate fraction, respectively, for virgin soil. Since smaller aggregates are preferentially removed by erosion, this study emphasizes the need for sustainable soil management practices that they will minimize nutrient loss when forest or pastures lands are converted to croplands.     

ASSESSMENTS OF THE RELATIVE VALUES OF COMPOUND NITROGEN-PHOSPHORUS FERTILIZERS FOR WHEAT PRODUCTION

A general procedure is developed for calculating optimal rates of application of compound fertilizers, containing several nutrients in fixed composition. The calculations are based on response surface models that have been obtained with single nutrient fertilizers. The relative values of alternative compounds can be assessed from the increases in profit that result from their use at optimal rates and this is preferable to simply comparing fertilizer compositions with that of an ideal mix of single nutrient fertilizers. The relative values of a range of standard nitrogen-phosphorus fertilizers are assessed for wheat production in southern New South Wales. The results indicate the need for a compound with a low nitrogen/phosphorus ratio of about 0.5. For the range of fertilizers considered it is concluded that it will generally be preferable to use superphosphate, supplementing with nitrogen fertilizer where N deficiency is suspected. The assumptions required for the calculation of optimal fertilizer rates are discussed.     

干旱区精河流域绿洲化过程中土壤养分时空变异研究

[目的]对干旱荒漠区不同土地利用方式下土壤养分时空特征进行研究,为绿洲土壤的科学施肥及更合理的土地资源开发利用提供理论依据,以促使土壤养分在精河流域平原绿洲系统中合理迁移和分布。[方法]以精河流域平原绿洲为靶区,基于GIS与地统计学方法,利用2003年和2018年不同土地利用方式下获取的土壤采样数据,对绿洲化过程中土壤养分(有机质、碱解氮、速效磷)的时空动态变化及重心迁移特征进行分析。[结果](1)2018年的土壤有机质、速效磷低于2003年,而碱解氮高于2003年。在空间上,各养分含量的高值区均出现在绿洲北部和西北部,低值区则主要位于绿洲边缘及南部区域;(2)对土壤养分综合分级评价结果显示,2003—2018年绿洲化过程中研究区土壤养分整体下降,中等及偏上水平的土壤养分重心沿精河向绿洲东北方向(艾比湖西南缘)及西北部的博乐绿洲方向迁移;(3)不同土地利用方式下,土壤养分含量均与土壤pH呈显著或极显著负相关关系,其中在草地、耕地和未利用地中呈极显著的差异(P<0.01),在林地中两者呈显著差异(P<0.05)。[结论]该研究对精河流域绿洲化过程中土壤养分变化和迁移特征进行的时空对比分析,有助于推进研究区平原绿洲耕地的利用和发展布局,为实现生态可持续发展提供重要参考。     

MODELLING FERTILISER DEMAND IN THE REPUBLIC OF IRELAND: A COST FUNCTION APPROACH

A translog cost function was used to obtain estimates of the own- and cross-price demand elasticities for nitrogen, phosphorus and potassium. The results indicated a mean value for the own-elasticities of —1.0, —0.6, —0.5 for N, P and K respectively. A test of the hypothesis of nutrient substitution was attempted. The test indicated that P and K were substitutable for N but not for each other. This result was corroborated by a zero elasticity of substitution estimate between phosphorous and potassium. A corollary of the results was the rejection on empirical grounds of the Cobb-Douglas specification for the input demand functions. The latter function has traditionally been used in analyses of this nature.     

东北典型黑土区耕地地力评价与障碍因素诊断

研究目的:从影响耕地地力的土壤管理、理化性质、土壤养分、剖面性状、立地条件和气候条件等6个方面选取13个评价指标对东北典型黑土区耕地地力进行综合评价,并在评价基础上进行障碍因素诊断,为今后定量化分析耕地地力障碍因素提供方法。研究方法:该研究运用层次分析法和模糊数学法等方法进行耕地地力评价,并引入障碍度模型对影响该区域耕地地力的障碍因素进行定量化分析。研究结果:(1)东北典型黑土区耕地地力整体呈现南高北低的趋势,其中以中等地(四、五、六、七等地)为主,占研究区总耕地面积的64.47%;其次为高等地(一、二、三等地),占研究区总耕地面积的28.31%;低等地(八、九、十等地)最少,只占研究区总耕地面积的7.22%;(2)对研究区评价指标体系中耕层厚度、有机质、有效磷、p H、灌溉能力、排涝能力6个指标进行障碍度分析,发现除有效磷和p H对耕地地力障碍作用不明显外,其他因素均有明显障碍作用,且障碍程度呈现一定的规律性。研究结论:(1)通过对研究区进行耕地地力评价,对东北典型黑土区的耕地数量和质量在空间分布特征上有了全面掌握,为今后耕地的合理利用提供了依据;(2)障碍度模型的引入为分析影响耕地地力的障碍因素提供了定量化的研究方法,为耕地地力保护和提升研究提供了方法支撑。     

北京农业废弃物现状与循环利用模式探讨

为了了解北京农业废弃物的现状,探讨农业废弃物的循环利用模式,根据统计数据与公开发表文献,利用作物秸秆籽粒系数与畜禽粪便排泄系数法对北京农业废弃物数量及养分进行了估算.结果表明:2008年北京农作物秸秆总量达220万吨,氮、磷、钾含量分别为2.0、1.1和2.7万吨,畜禽粪便总量达786万吨,氮、磷、钾含量分别为5 47...     

Sequential Adoption of Site-Specific Technologies and Its Implications for Nitrogen Productivity: A Double Selectivity Model

This paper analyzes the sequential decision to adopt two site-specific technologies, soil testing and variable rate technology, and the impact of adoption on nitrogen productivity. The results indicate that while farm location was a key variable influencing adoption of soil testing, farm size, human capital, and innovativeness of farmers had a significant impact on adoption of variable rate technology in four Midwestern states. A double selectivity model applied to correct for sample selection bias shows that adoption leads to significant gains in nitrogen productivity for farms with below average soil quality but statistically insignificant gains for farms with above average soil quality.