Reducing peak supplemental irrigation demand by extending sowing dates

Supplemental irrigation (SI) is a common practice in the dry environments and aims at improving and stabilizing rainfed crops by adding small amounts of water to rainfed crops during times when rainfall fails to provide sufficient moisture for normal plant growth. Results from long-term research in experimental stations and farmer fields showed substantial increases in rainfed crop yields and water use efficiency in response to SI. Nevertheless, SI comes at a cost.The date of sowing winter wheat in a rainfed Mediterranean-type environment depends upon the onset of rainfall. The optimal date for achieving highest yield under rainfed conditions is around mid-November. However, farmers tend to sow wheat later than this date because of the delay and/or unreliability of initial rains. With SI, early sowing and crop establishment can be ensured. However, early sowing of all the fields’ results in higher water demand during a very short period in spring because all the fields will be at the peak use rate. Spreading out dates of sowing allows peak water demand to occur over a longer period, thus reducing the discharge and the size of irrigation system needed, and hence improves the economics of this practice. In this paper, the impact of adopting a multi-sowing date strategy on farm water demand and crop production is considered. A simplified optimization model solved by linear programming is presented. Four-years’ data (1992–1996) from field experimental research conducted on bread wheat in northern Syria have been used in the analysis.We showed that a multi-sowing date strategy has reduced the peak farm water demand rate by more than 20%, thus potentially reducing irrigation system capacity and/or size. Alternatively, the water demand rate of a larger area can be met with the same water supply. However, optimal sowing dates that minimize farm water demand rate do not always maximize total farm production. The outcome depends on crop water requirements and yield for each sowing date. Furthermore, this selection is greatly influenced by the level of water scarcity. The approach used can help in reducing the cost of irrigation and improving the efficiency of water use in SI.     

播期对夏玉米生长及产量品质的影响

为研究河南豫北平原地区玉米的适宜播期,选取当地大范围种植品种郑单958为供试品种,比较播期推迟（（5月31日、6月10日、6月20日和6月30日）对玉米生长发育的气象条件、叶面积指数、光合特性、产量形成和籽粒品质的影响,以期为玉米优质高产提供参考和指导。研究结果表明,近20年研究区各播期花期高温平均发生频率分别为18.5%、18%、6.2%、3.4%,各播期花期连阴雨平均发生频率分别为25.4%、25.8%、21.1%、18.7%。随着播期推迟,叶面积指数和光合势呈现先升后降的趋势,B3处理叶面积指数和光合势较大。B1-B3处理玉米产量差异性不大,B4处理与其他播期相比产量下降极显著。B3处理玉米的氨基酸、蛋白质、淀粉等含量均较高,为保证玉米有充足的光合效率,达到较高的产量和优质的籽粒品质,郑单958播期最晚可推迟至6月20日。     

Calibration and use of CROPGRO-soybean model for improving soybean management under rainfed conditions

Crops such as soybean (Glycine max L.) are grown predominantly under rainfed conditions where water is a major limiting factor and the interannual variability in rainfall pattern is high. Crop modeling has proven a valuable tool to evaluate the long-term consequences of weather patterns, but the candidate crop models must be tested and calibrated for new regions prior to their use as extrapolation tools to predict optimum cultivar choice and sowing dates. The objectives of this paper were to calibrate the CROPGRO-soybean model for growth and yield under rainfed conditions in Galicia, northwest Spain, and then to use the calibrated model to establish the best sowing dates for three cultivars at three locations in this region. The starting point of the calibration process was the CROPGRO-soybean version previously calibrated for non-limiting water conditions. The original model, when simulated versus rainfed soybean field data sets, tended to simulate more severe water stress than actually occurred. In order to calibrate growth and yield for the actual soil we tried several ways for the modelled crop to have access to more water. Modifications were made on soil depth, water holding capacity, and root elongation rate. In addition, other changes were made to predict accurately the observed water-stress induced acceleration of maturity. Long-term simulations with recorded weather data showed that soybean is more sensitive to planting date under irrigated than rainfed management, in the three studied Galician locations.     

Water use efficiency of winter-sown chickpea under supplemental irrigation in a mediterranean environment

Chickpea is one of the major legume crops grown in the West Asia and North Africa (WANA) region. It has considerable importance as a food, feed and fodder. Traditionally, it is sown in spring as a rainfed crop in the region, which has highly variable and often insufficient rainfall. It is, therefore, largely raised on residual moisture, which results in low and variable yields and discourages farmers from investing inputs in its production. In the early 1990s, a winter-sown chickpea technology was developed that outweighs spring-sown chickpea in terms of productivity, water use efficiency and other traits. Limited supplemental irrigation can, however, play a major role in boosting and stabilizing the productivity of both spring-sown and winter-sown chickpea. Therefore, we investigated the effect of supplemental irrigation and sowing date on yield and water use efficiency in winter-sown chickpea.An experiment was carried out over four cropping seasons (1997–2001) at ICARDA’s main station at Tel Hadya, Aleppo, northern Syria (mean annual rainfall 330 mm). A cold-tolerant chickpea cultivar with improved resistance to ascochyta blight (ILC 3279, released as Ghab 2 in Syria) was grown in rotation with wheat. The experiment included three sowing dates (late November, mid-January, and late February) and four levels of supplemental irrigation (SI): full SI, 2/3 SI, 1/3 SI, and no SI, i.e. rainfed. The plots were replicated three times in a split-plot design, with date of sowing being the main plot treatment. Soil water content was monitored at approximately at 7–14-day intervals using a neutron probe. Crop evapotranspiration was determined for each subplot during each time interval, from sowing to harvest, using the soil-water balance equation. Water use efficiency was determined as the ratio of crop yield per unit area to seasonal evapotranspiration.The results showed that chickpea yield per unit area increases with both earlier sowing and increased SI. However, water use efficiency under supplemental irrigation decreases with earlier sowing, due to the relatively large increase that occurs in the amount of evapotranspiration at early sowing dates. The study’s results indicated that a 2/3 SI level gives the optimum water use efficiency for chickpea under supplemental irrigation. Under rainfed conditions, however, it was found that sowing chickpea around mid-January resulted in the highest WUE. The analysis also proposed a function, based on regression, which relates winter-sown chickpea yield to water use and which is applicable under both supplemental and rainfed conditions.     

Seed yield and water use efficiency of canola (Brassica napus L.) as affected by high temperature stress and supplemental irrigation

The effects of high temperature stress and supplemental irrigation on seed yield and water use efficiency (WUE) of canola (Brassica napus L.) were studied in a field experiment conducted for 2 years. The experiment was a randomized complete block design arranged in split plot, conducted at Agricultural Research Station of Gonbad, Iran. It was arranged in two conditions, i.e. supplemental irrigation and rainfed. Two cultivars of canola (Hyola401 and RGS003) as subplots were grown at five sowing dates as main plots. The sowing dates were 9 November, 6 December, 5 January, 4 February and 6 March in 2005-2006 and 6 November, 6 December, 5 January, 4 February and 6 March in 2006-2007, to have a wide range of environmental conditions around flowering and seed filling periods, and to coincide reproductive stages of the crop with high temperature stress. Seed yield was improved due to field management practices, such as supplemental irrigation and optimum sowing date. Supplemental irrigation was an efficient practice to mitigate water stress, and to increase aboveground dry matter and seed yield. There was a strongly negative relationship between seed yield and air temperature during reproductive stages. Delay in sowing led to more rapid developmental of canola, decreased aboveground dry matter, leaf area index (LAI), harvest index (HI), WUE, and seed yield. Achieving a high aboveground dry matter was an essential prerequisite for high reproductive growth and a high seed yield. Greater seed yield and WUE at first sowing date were associated with greater LAI and aboveground dry matter, and lower temperatures during reproductive stages. The results support the view that WUE can be used as an indirect selection criterion for seed yield in genotypic selection.     

播期对不同玉米品种生长发育及产量的影响

通过调整播期,研究影响玉米生长发育和产量形成的气候因素,尤其是高温条件。试验选取京农科728、登海618、郑单958和先玉335共4个主栽玉米品种为材料,分别在2019年6月5日（T1）、6月15日（T2）和6月25日（T3）3个播期处理种植。结果表明,4个玉米品种的生育期,随着播期的推迟均不同程度延长。成熟期干物质积累量,4个玉米品种的叶片和茎秆在不同的播期没有明显差别,但籽粒和穗4个品种干物质积累量早播处理比晚播处理积累量大,可能是因为早播处理比晚播处理时段的温度要高。在玉米穗粒数、百粒质量和产量上,品种和播期处理对其影响达极显著水平。品种和播期处理对穗粒数、百粒质量和产量表现出极显著的交互作用。京农科728、登海618、郑单958和先玉335品种的穗粒数、百粒质量和产量最大值均为T2处理,最低均为T1处理,在产量性状上可能是因为T1处理在开花授粉阶段正好遇到连续高温天气,导致T1处理结实性较差。由此可见,在玉米生长发育和产量形成时,高温对其影响较大,在没有遇到高温的情况下,适时早播对玉米产量的提高将更有利。      

高寒荒漠区混播草地土壤水热分布特征

探究土壤水热变化规律及特征有助于人工草地高效利用水热资源。利用数理统计和多重分形理论，对比分析了青海省乌兰县藜麦毛苕子混播和燕麦箭筈豌豆混播草地土壤水热变化对降雨的响应及其分布特征。结果表明，降雨对草地土壤含水率的影响具有明显的延迟效应；土壤含水率变化属于中等强度变异，呈“薄尾”分布，土壤含水率的变异主要由高值分布造成，并且主要为短距离变异；与燕麦箭筈豌豆混播相比，藜麦毛苕子混播土壤含水率较高，并且对降雨的表蓄作用较强。降雨对深层土壤温度的影响具有一定的延迟性；土壤温度属于中等强度变异，呈“厚尾”分布，其中0～10 cm土层变异强度最大，深层土壤温度主要为短距离变异，土壤温度变异主要由高值分布造成。与燕麦箭筈豌豆混播相比，藜麦毛苕子混播土壤温度较高，并且受降雨影响较小。综上，混播模式对草地土壤水热的影响存在差异，藜麦毛苕子混播较燕麦箭筈豌豆混播在土壤水热利用方面具有一定优势。该研究结果可为高寒荒漠区人工草地充分利用土壤水热资源提供理论依据。      

An integrated model-approach to the effect of water management on crop yield

Quantifying the effect of drainage on crop yield is of essential importance in agricultural management. In this article a model is described with which this effect can be computed. For both arable land and grassland the factors acting in spring, summer and autumn are dealt with separately.Arable land. In spring sowing date is the main factor affecting the crop yield. Sowing date depends on the tillage conditions of the soil toplayer. By means of an existing model, the course in time of the soil water tension of the upper layer is simulated in connection with rainfall, evaporation, drain depth and drain intensity data. Using specific criteria on minimum soil water tension for tillage operations, the dates and number of workable days can be established from the model output. The expected yield depression is then derived, using an experimental relationship between yield depression and number of days of sowing delay.During the growing season the yield directly depends on the magnitude of the actual evapotranspiration. This value can be computed by means of a known evapotranspiration model for various drought frequencies, groundwater table depths in spring, drain intensities and amounts of water supplied. The yield can be obtained from the relationship between yield and relative evapotranspiration. Combining this yield with the yield depression obtained by means of the workability model gives the actual yield.In autumn crop yield is influenced by the working conditions during harvest. Via the workability model, the dates and the number of days available for harvesting are determined. Yields are derived from an experimental relationship between yield depression and number of days of earlier harvesting. An example is given for summer cereals growing on a heavy sandy loam soil under meteorological conditions prevailing in The Netherlands.Grassland. The effect of shallow groundwater table depths in winter and spring on the yield of the first and second cut can be determined with the workability model in an identical manner to that given for arable land. Because of lack of data, a slightly different approach was followed in this paper. With the workability model the course of groundwater table depth during winter and spring can be simulated and the mean depth determined. From the relation between yield depression and mean groundwater table depth over the period November through May the yield depression can be found. Combining this with the yield obtained with the evapotranspiration model gives the actual yield. An example representative for The Netherlands is given for grass on peat soil.     

Water use and water use efficiency of sweet corn under different weather conditions and soil moisture regimes

Plant growth and development are influenced by weather conditions that also affect water use (WU) and water use efficiency (WUE) and ultimately, yield. The overall goal of this study was to determine the impact of weather and soil moisture conditions on WU and WUE of sweet corn (Zea mays L. var rugosa). An experiment consisting on three planting dates was conducted in 2006 at The University of Georgia, USA. A sweet corn genotype sh2 was planted on March 27 under irrigated and rainfed conditions and on April 10 and 25 under irrigated conditions only. Soil moisture was monitored using PR2 probes. Rainfall and irrigation were recorded with rain gauges installed in the experimental area while other weather variables were recorded with an automatic weather station located nearby. A water balance was used to obtain the crop's daily evapotranspiration (ETc). WUE was calculated as the ratio of fresh and dry matter ear yield and cumulative ETc. The potential soil moisture deficit (Dp) approach was used to determine the crop's moisture stress. Results were analyzed using a single degree freedom contrast, linear regression, and the least significant difference. WU and WUE of sweet corn were both markedly affected by the intra-seasonal weather variability and Dp. For both variables, significant (p < 0.05) differences were found between planting dates under irrigated conditions and between the irrigated and rainfed treatments. WU was as high as 268 mm for the April 10 planting date under irrigated conditions and as low as 122 mm for the March 27 planting date under rainfed conditions. The maximum soil moisture deficit was reached at the milky kernel stage and was as high as 343 mm for the March 27 planting date under rainfed conditions and as low as 260 mm for the April 10 planting date under irrigated conditions. Further work should focus on the impact of the intra-seasonal weather variability and soil moisture conditions during different crop stages to determine critical periods that affect yield.     

Validation and testing of the AquaCrop model under full and deficit irrigated wheat production in Iran

Accurate crop development models are important tools in evaluating the effects of water deficits on crop yield or productivity and predicting yields to optimize irrigation under limited available water for enhanced sustainability and profitable production. Food and Agricultural Organization (FAO) of United Nations addresses this need by providing a yield response to water simulation model (AquaCrop) with limited sophistication. The objectives of this study were to evaluate the AquaCrop model for its ability to simulate wheat (Triticum aestivum L.) performance under full and deficit water conditions in a hot dry environment in south of Iran, to study the effect of different scenarios of irrigation (crop growth stages and depth of water applied) on wheat yield. The AquaCrop model was evaluated with experimental data collected during the three field experiments conducted in Ahvaz. The AquaCrop model was able to accurately simulate soil water content of root zone, crop biomass and grain yield, with normalized root mean square error (RMSE) less than 10%. The analysis of irrigation scenarios showed that the highest grain yield could be obtained by applying four irrigations (200 mm) at sowing, tillering, stem elongation and flowering or grain filing stages for wet years, four irrigations (200 mm) at sowing, stem elongation and flowering stages for normal years and six irrigations (300 mm) at sowing, emergence, tillering, stem elongation, flowering and grain filing stages for dry years. The least amount of irrigation water to provide enough water to response to evaporative demand of environment and to obtain high WUE for wet, normal and dry years were 100, 200 and 250 mm, respectively.     

Combining remote sensing-simulation modeling and genetic algorithm optimization to explore water management options in irrigated agriculture

We present an innovative approach to explore water management options in irrigated agriculture considering the constraints of water availability and the heterogeneity of irrigation system properties. The method is two-folds: (i) system characterization using a stochastic data assimilation procedure where the irrigation system properties and operational management practices are estimated using remote sensing (RS) data; and (ii) water management optimization where we explored water management options under various levels of water availability. We set up a soil–water–atmosphere–plant model (SWAP) in a deterministic–stochastic mode for regional modeling. The distributed data, e.g. sowing dates, irrigation practices, soil properties, depth to groundwater and water quality, required as inputs for the regional modeling were estimated by minimizing the residuals between the distributions of field-scale evapotranspiration (ET) simulated by the regional application of SWAP, and by surface energy balance algorithm for land (SEBAL) using two Landsat7 ETM+ images. The derived distributed data were used as inputs in exploring water management options. Genetic algorithm was used in data assimilation and water management optimizations. The case study was conducted in Bata minor (lateral canal), Kaithal, Haryana, India during 2000–2001 rabi (dry) season. Our results showed that under limited water condition, regional wheat yield could improve further if water and crop management practices are considered simultaneously and not independently. Adjusting sowing dates and their distribution in the irrigated area could improve the regional yield, which also complements the practice of deficit irrigation when water availability is largely a constraint. This result was also found in agreement with the scenario that water is non-limited with the exception that the farmers have more degrees of freedom in their agricultural activities. An improvement of the regional yield to 8.5% is expected under the current scenario.     

Management of cruciferous cover crops by mowing for soil and water conservation in southern Spain

In recent years, the use of cover crops in Mediterranean olive orchards has increased due to serious soil erosion problems and surface water contamination by herbicides. In these areas, the annual precipitation regime is strongly seasonal, with dry summers that require killing the cover crop before it competes with the trees for water. Cruciferous species are being introduced as cover crops in southern Spain, and their management by mowing could reduce the use of herbicides. However, the use of mowing as a management system requires an understanding of the phenology of these species to identify the most suitable mowing date to derive the greatest possible soil water content. The aims of this study were the following: (1) to assess the susceptibility of cruciferous species to mowing, their regrowth ability and the persistence of their residues on the soil surface after mowing, and (2) to identify the best mowing date for the cover crops in relation to the soil moisture content in the environmental conditions of southern Spain. For these purposes, the emergence, ground cover, biomass and regrowth after two mowing dates of common mustard (Sinapis alba L. subsp. mairei), rocket (Eruca vesicaria), radish (Raphanus sativus) and Ethiopian mustard (Brassica carinata) were evaluated in field trials during 2001/2002. In addition, during 2002/2003 and 2003/2004, the moisture content of soil sowed with common mustard and rocket cover crops was assessed at different mowing dates and compared with a bare soil control. Common mustard was the most favourable species for management by mowing due to its lack of regrowth after mowing. Early mowing (March 10th) reduced soil moisture due to the regrowth of the cover crop, fast decomposition of cover residues and weed proliferation. Late mowing (April 24th) led to little or no regrowth of the cover crops, large biomass and high persistence of cover residues, which provided effective soil ground cover, avoided the emergence of spring-summer weeds and helped retain soil moisture, reaching a similar water content to bare soil. These results suggest that cruciferous cover crops killed by mowing in late April can be used to replace no-tillage bare soil management systems to reduce the use of herbicides and preserve soil and water quality.     

Long-term effects of different irrigation strategies on yield components, vine vigour, and grape composition in cv. Cabernet-Sauvignon (Vitis vinifera L.)

There are still some traditional vine-growing areas in Spain in which water-stressed vines are considered to produce berries with the highest quality must. To assess vine response to water availability, measured in terms of crop yield, vegetative development, and grape composition, five different irrigation treatments were evaluated over a five-year period in a Cabernet-Sauvignon vineyard in the Madrid region (Spain): no-irrigation (T0), water provided at 20?% of the reference evapotranspiration (ETo) (T20), water provided at 45?% of the ETo (T45), water provided at 20?% of the ETo until veraison and at 45?% thereafter (T20-45), and water provided at 45?% until veraison and 20?% thereafter (T45-20). A yield increment was observed with increasing water volumes. The T45 vines returned a consistent yield of around 8 t/ha, and a mean shoot weight of 30–50?g. The T0 and T20 plants showed reduced yields and vegetative growth in most years (yields being the most acutely affected). Berry weight was the yield component most influenced by water availability. In years of low rainfall, fertility was markedly reduced in the T0 vines. Providing a smaller irrigation volume before or after veraison (the T20-45 and T45-20 treatments) led to reductions in berry weight, cluster weight, and shoot weight over the last 3?years of the trial. Berry composition was almost unaffected by irrigation strategy. Taking into account yield, water use efficiency, and berry composition, the T45-20 treatment was the most efficient irrigation strategy.     

On-farm assessment of regional and seasonal variation in sunflower yield in Argentina

Using an on-farm approach, we investigated constraints to actual yield of sunflower in six agroecological zones within the Argentine Pampas during three growing seasons. In 249 large, grower-managed paddocks, we quantified a series of variables related to: (1) crop phenology, growth, and yield; (2) the physical and biological environment; and (3) management practices. Variation in yield among zones and seasons was analysed on the basis of four biologically-founded assumptions: (1) grain number accounts for a large proportion of the variation in yield; (2) grain number is associated with a photothermal coefficient, Q=R (T-T_b)⁻¹, where R and T are average solar radiation and air temperature respectively, during the 50-day period bracketing anthesis; and T_b is a base temperature; (3) crop growth and yield are proportional to light interception, and therefore proportional to canopy ground cover; and (4) yield is proportional to the fraction of seasonal rainfall that occurs after anthesis. Average yield ranged from 1.1 to 2.7 t ha⁻¹, grain number from 2400 to 5400 m⁻², individual grain mass between 40 and 69 mg and grain oil concentration between 42 and 52%. Grain number accounted for 43% of the variation in average yield while Q accounted for 23% of the variation in grain number. Low yield was associated with deficient ground cover in 25% of the crops; part of the remaining variation in yield was accounted for by sets of measured variables particular to each zone, including soil shallowness, low available P, low initial water content, weeds and diseases — chiefly Verticillium wilt (Verticillium dahliae) and Sclerotinia head rot (Sclerotinia sclerotiorum). Across zones and seasons, the proportion of seasonal rainfall occurring after anthesis accounted for 28% of the variation in crop yield. A trade-off is highlighted whereby beneficial effects of rainfall that favours growth and yield may be offset by the detrimental effect of abundant moisture that favours major fungal diseases. We emphasised the value of combining experimental studies — which provide biological background in the form of working hypotheses — with on-farm research that realistically quantifies yield response to key factors.     

播期和播深对冬小麦越冬前生长性状的影响

为评价播期和播深对冬小麦越冬前生长性状的影响,以农大211冬小麦为试验材料,于2015-2017年在中国农业大学北京上庄实验站进行了4个播期水平(9月23日、10月3日、10月13日和10月23日)、3个播深水平(2、4、6 cm)的随机区组大田试验,探究不同栽培措施对越冬前冬小麦各生长指标(单株叶面积、主茎叶龄、分蘖...     

降水的随机模拟及其在灌溉中的应用

本文研究了一个由简单的产生逐日降水的方法用在水量平衡方程中确定作物的灌溉量和灌溉时间的模拟模型。该降水模型用月平均的气象资料产生逐日降水,并且在水量平衡模型中将蒸发蒸腾量值进行了随机化处理。对陕西省的扶风县和大荔县分别进行了23年和29年的冬小麦和夏玉米的灌溉模拟。利用模拟结果分析了灌水量和最可能产生缺水的时间。此方法可用于半干旱地区在各种降水情况下的灌溉模拟。     

Water storage in soils during the fallow: prediction of the effects of rainfall pattern and soil conditions in the Ebro valley of Spain

Fallowing remains a feature of dryland cereal agriculture in some low rainfall areas of central and northern Spain. To complement the limited number of measurements of water stored during the fallow, we developed a physically based simulation model to estimate the effects of variations in rainfall, soil characteristics and surface conditions on water storage in the profile. Mean annual rainfall in the locations investigated varied from ca. 300–500 mm and the mean amount of water stored during the last year of a bare fallow ranged from 1–48 mm, depending on soil and climate. The standard deviations of these amounts, each based on 25 simulations, varied from 11–39 mm. Rainfall in the last 3 months of the fallow was the principal cause of this year to year variation in storage. Surface stoniness and crop residues decreased evaporation from the soil and increased storage: there was very little drainage. These findings are consistent with measured water storage in soils in this part of Spain, and other areas of the world with similar climates and agricultural practices. Based on barley yield/rainfall regressions for data from a dry area in the Ebro valley, we estimated that the annual yields from a crop–fallow system would be 15% greater than those from annual cropping. For fallowing to be economic, yields per crop would need to be about twice those obtained with annual cropping. There may be yield benefits from fallowing apart from those resulting from extra water storage in the soil. Unless such benefits can be demonstrated, fallowing would appear to be uneconomical in this area of Spain.     

旱作条件下水稻生长指标、产量对播期的响应特征

[目的]研究播期与品种类型对生育期农艺性状的影响,为水稻旱作条件下不同类型品种选择适宜播期提供科学依据.[方法]以早熟粳稻、中熟粳稻、晚熟粳稻3种类型的水稻为供试材料,设置5个播期(分别为4月25日、30日、5月5日、10日、15日),研究各品种类型水稻旱作产量、生育表现及农艺性状的特点.[结果]水稻产量表现为早熟粳稻...     

The use of a phenology model and of risk analyses for planning buckwheat (Fagopyrum esculentum) sowing dates in Alpine areas

A published temperature-dependent phenology model constructed for representing buckwheat (Fagopyrum esculentum) development has been calibrated. The model considers the phenophases of sowing to emergence, of emergence to first anthesis, and of first anthesis to physiological maturity. It is used for the strategic planning of buckwheat production in Alpine areas and predicts the latest possible sowing dates in areas of the Swiss cantons of the Grisons and of the Ticino as well as of the Italian province of Sondrio. The area-specific date is calculated by taking into account a probability of 1% for crop failure which occurs when the crop is exposed to temperatures < 2.5°C before it reaches physiological maturity. To account for operational constraints, we have anticipated the calculated sowing date by 10 days. During a given year, buckwheat should be considered as the only crop at high altitudes, while it can be cultivated as a catch crop, after cereals for example, at low altitudes. The results show that the model efficiently makes use of existing information and provides useful recommendations for experimental work. The model is also a valuable tool for farmers interested in growing buckwheat in the areas under study.     

Optimizing the yield of winter wheat by regulating water consumption during vegetative and reproductive stages under limited water supply

To ensure sustainable agricultural water use in water shortage regions, practices of deficit irrigation should be adopted. This study investigated the performance of winter wheat (Triticum aestivum L.) under limited water supply from 2005 to 2011, a six-season field test on the North China Plain. The test was comprised of four treatments: rain-fed, single irrigation applied at sowing to obtain a good level of soil moisture at the start of crop growth (I1s), single irrigation applied during recovery to jointing (I1r), and full irrigation supplied as three irrigations (control, I3). The results showed that grain yield was significantly correlated with rainfall before heading and with evapotranspiration (ET) after heading (P < 0.01) under rain-fed conditions. The average contribution of soil water stored before sowing to seasonal ET was 90, 103, and 145 mm for rain-fed, I1s, and I1r, respectively, during the six seasons. A smaller root length density (RLD), which restricted utilization of deep soil water by the crop, was one of the reasons for the lower yield with rain-fed and I1s treatments compared with the I1r treatment in dry seasons. The results also showed that the limited irrigation applied from recovery to jointing stage (Treatment I1r) significantly promoted vegetative growth and more efficient soil water use during the reproductive (post-heading) stage, resulting in a 21.6 % yield increase compared with that of the I1s treatment. And although the average yield of the I1r treatment was 14 % lower than that of the full irrigation treatment, seasonal irrigation was reduced by 120–140 mm. With smaller penalties in yield and a larger reduction in applied irrigation, I1r could be considered a feasible irrigation practice that could be used in the NCP for conservation of groundwater resources.