CERES-Rice模型中宜香3728水稻遗传特性参数调试与校验

利用在湖北省房县所开展的两年（2012、2013年）田间试验,对水稻品种宜香3728在CERES-Rice模型中的遗传特性参数进行了调试与校验。首先,根据2013年田间实测数据,如关键生育期及其叶面积指数、地上部干物质量和产量等,采用“GLUE+试差法”对宜香3728的遗传特性参数进行了调试。当达到设定的误差控制标准时（10%以内）,停止调试,并将此时模型中的遗传特性参数作为调试结果。然后,再应用2012年实测数据对此组遗传特性参数进行校验。模型模拟值与田间实测值之间的对比关系表明此组遗传特性参数基本准确,可用于表征宜香3728水稻品种在房县的遗传特性。研究成果为利用CERES-Rice模型在房县及周边同类地区开展相关研究工作奠定了基础,同时也可为CERES-Rice模型在其他地区的本地化应用提供借鉴。      

Evaluation of CERES-Wheat and CropSyst models for water–nitrogen interactions in wheat crop

Crop simulation models can provide an alternative, less time-consuming and inexpensive means of determining the optimum crop N and irrigation requirements under varied soil and climatic conditions. In this context, two dynamic mechanistic models (CERES (Crop Environment REsource Synthesis)-Wheat and CropSyst (Cropping Systems Simulation Model)) were validated for predicting growth and yield of wheat (Triticum aestivum L) under different nitrogen and water management conditions. Their potential as N and water management tool was evaluated for New Delhi representing semi-arid irrigated ecosystems in the Indo-Gangetic Plains. The field experiment was carried out on a silty clay loam soil at the Research Farm of the Indian Agricultural Research Institute, New Delhi, India during 2000–2001 to collect the input data for the calibration and validation of both the models on wheat crop (variety HD 2687). The models were evaluated for three water regimes [I4 (4 irrigations within the growing season), I3 (3 irrigations within the growing season) and I2 (2 irrigations within the growing season)] and five N treatments (N₀, N₆₀, N₉₀, N₁₂₀ and N₁₅₀). Both the models were calibrated using data obtained from the treatments receiving maximum nitrogen and irrigations, i.e., N₁₅₀ and I4 treatments. The models were then validated against other water and nitrogen treatments. For performance evaluation, in addition to coefficient of determination (R²), root mean square error (RMSE), mean absolute error (MAE) and Wilmot's index of agreement (IoA) were estimated. Both CERES-Wheat and CropSyst provided very satisfactory estimates for the emergence, flowering and physiological maturity dates. For CERES-Wheat overall prediction (pooled result of the three water regimes) of grain yield was satisfactory with significant R² values (0.88). The model, however, under estimated the biomass under all water regimes and N levels except for N₀ level, under which biomass was overpredicted. CropSyst predicted yield and biomass of wheat more closely than CERES-Wheat. The combined RMSE for the three water regimes between predicted and observed grain yield was 0.36 Mg ha⁻¹ for CropSyst as compared to 0.63 Mg ha⁻¹ for CERES-Wheat. Similarly, RMSE between observed and predicted biomass by CropSyst was 1.27 Mg ha⁻¹ as compared to 1.94 Mg ha⁻¹ between observed and predicted biomass by CERES-Wheat. Wilmot's index of agreement (IoA) also indicated that CropSyst model is more appropriate than CERES-Wheat in predicting growth and yield of wheat under different N and irrigation application situations in this study.     

Incorporation of ridge and furrow method of rainfall harvesting with mulching for crop production under semiarid conditions

A plastic-covered ridge and furrow rainfall harvesting (PRFRH) system combined with mulches was designed to increase water availability to crops for improving and stabilizing agricultural production in the semiarid Loess region of northwest China. The system was built by shaping the soil surface with alternate ridges and furrows along the contour. The plastic-covered ridges served as a rainfall harvesting zone and furrows as a planting zone. Some materials were also used to mulch the furrows to increase the effectiveness of the harvested water. This system can make better utilization of light rain by harvesting rainwater through the plastic-covered ridge. The field experiment (using corn as an indicator crop) showed that grain yields in the PRFRH system with mulches in 1998 and 1999 were significantly higher than the controls, with an increase of 4010–5297 kg per ha (108–143%). In most treatments, the water use efficiencies (WUE) were in excess of 2.0 kg m⁻³. The WUE values of corn in this system were 1.9 times greater than the controls in 1998 and 1.4 times greater than the controls in 1999. The plastic-covered ridge led to a yield increase of 3430 kg per ha (92%) in 1998 and of 1126 kg per ha (21%) in 1999 compared with the uncovered ridge. On average, the additional mulches in the furrow brought about a yield increase of 8–25%. Based on the results of this study and other researches, this technique can increase corn grain yield by 60–95% in drought and average years, 70–90% in wet years, and 20–30% in very wet years. The PRFRH system had the potential to increase crop yield and produced greater economic benefit, therefore it could be used in regions dominated by light rainfall of low intensity where crops generally fail due to water stress.     

Integrated management of irrigation water and fertilizers for wheat crop using field experiments and simulation modeling

The reported study aimed at developing an integrated management strategy for irrigation water and fertilizers in case of wheat crop in a sub-tropical sub-humid region. Field experiments were conducted on wheat crop (cultivar Sonalika) during the years 2002–2003, 2003–2004 and 2004–2005. Each experiment included four fertilizer treatments and three irrigation treatments during the wheat growth period. During the experiment, the irrigation treatments considered were I₁ = 10% maximum allowable depletion (MAD) of available soil water (ASW); I₂ = 40% MAD of ASW; I₃ = 60% MAD of ASW. The fertilizer treatments considered in the experiments were F₁ = control treatment with N:P₂O₅:K₂O as 0:0:0 kg ha⁻¹, F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha⁻¹; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha⁻¹ and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha⁻¹. In this study CERES-wheat crop growth model of the DSSAT v4.0 was used to simulate the growth, development and yield of wheat crop using soil, daily weather and management inputs, to aid farmers and decision makers in developing strategies for effective management of inputs. The results of the investigation revealed that magnitudes of grain yield, straw yield and maximum LAI of wheat crop were higher in low volume high frequency irrigation (I₁) than the high volume low frequency irrigation (I₃). The grain yield, straw yield and maximum LAI increased with increase in fertilization rate for the wheat crop. The results also revealed that increase in level of fertilization increased water use efficiency (WUE) considerably. However, WUE of the I₂ irrigation schedule was comparatively higher than the I₁ and I₃ irrigation schedules due to higher grain yield per unit use of water. Therefore, irrigation schedule with 40% maximum allowable depletion of available soil water (I₂) could safely be maintained during the non-critical stages to save water without sacrificing the crop yield. Increase in level of fertilization increases the WUE but it will cause environmental problem beyond certain limit. The calibrated CERES-wheat model could predict the grain yield, straw yield and maximum LAI of wheat crop with considerable accuracy and therefore can be recommended for decision-making in similar regions.     

Water–yield relationships and optimal water management for winter wheat in the Loess Plateau of China

High evaporative demand and limited precipitation restrict the yield of winter wheat (Triticum aestivum L.) grown in the Loess Plateau of China under semiarid climatic conditions. Grain yield can be improved by effective water management practices. A 13-year field experiment was conducted at the CERN Changwu Agro-ecological Experimental Station of the Loess Plateau to determine optimal irrigation strategies under limited water supply and to develop relationships among grain yield (Y), seasonal evapotranspiration (SET) and water-use efficiency (WUE). The experiment consisted of five irrigation treatments and three blocks. Measurements included grain yield, soil water content at various depth intervals in the 0–3,000 mm layer, irrigation amount, and precipitation. Results showed that winter wheat grown in this area experienced serious water stress during critical growth stages for the no-irrigation treatment. The amount and timing of irrigation had an important effect on grain yield, but significant differences in yield were not observed between the three-irrigation and the four-irrigation treatments. Grain yield was linearly related (R²=0.66) to SET, but differences in WUE were not significant for any of the treatments. The relationship between WUE and Y was best represented by a second order polynomial (R²=0.65) consisting of a nearly linear portion between 1.5 and 5.0 Mg ha^–1. Optimum water management of winter wheat in the Loess Plateau should consist of three 87.5 mm irrigations applied at stem elongation, booting, and anthesis.Communicated by J.E. Ayars     

The effect of sowing date,irrigation and cultivar on the growth and yield of wheat in the Namoi River Valley,New South Wales

Summary A factorial experiment which examined the effects of sowing date, cultivar and irrigation frequency on the growth and grain yield of irrigated wheat was conducted at Narrabri, New South Wales. Irrigation scheduling was based on morning values of leaf water potentials (_l): plots were watered when _l, had fallen to either –0.8 MPa or –0.4 MPa or were not irrigated during the season.Maximum leaf areas, tiller numbers and total dry matter production were increased by more frequent irrigation, but subsequent tiller death and leaf senescence were generally not reduced by increasing watering. A delay in sowing from 23 June to 23 July reduced yields by 20%, on average. More frequent irrigation increased yields at both sowing dates, but a high protein, locally bred wheat (Songlen) responded less than a cultivar derived from the CIMMYT program (WW 15). The highest yield for Songlen was 570 g m^–2 which was lower than the highest yield for WW 15 (730 g m^–2); both were obtained from the –0.4 MPa treatment sown on 23 June. Compared with irrigated wheat grown in Mexico or southern New South Wales, dry matter production after anthesis at Narrabri was low. It was suggested that high temperatures after anthesis may limit post-anthesis productivity and subsequently, grain yields. The results of this experiment suggested that yields of irrigated wheat in the lower Namoi Valley can be improved through better irrigation management and varietal improvement, but the magnitude of this response may be limited by high spring temperatures.     

不同生育期干旱对冬小麦产量及水分利用效率的影响

用盆栽对冬小麦不同生育阶段进行不同程度水分调亏试验结果表明 :拔节—孕穗期、抽穗—扬花期和灌浆—成熟 3个阶段内 RW上限为 4 0 %、5 0 %、60 %的水分亏缺均引起了产量的极显著下降 ,而且水分亏缺越严重 ,产量降低越大。在 3个生育阶段内进行 RW上限为 4 0 %的水分调亏减产幅度都很大 ,而且 3个生育阶段之间差异不明显 ;进行 5 0 %、60 %水分调亏 ,其减产程度则与生育期有关。灌浆—成熟期的减产程度大于前二个时期 ,这可能与前二个阶段复水后作物的补偿生长有关。不同生育期水分亏缺对冬小麦产量构成因素的影响也不同 ,拔节—扬花期水分亏缺主要减少了穗粒数 ,灌浆—成熟阶段的水分亏缺主要减少了千粒重     

Test of AquaCrop model in simulating biomass and yield of water deficient and irrigated barley (Hordeum vulgare)

With the current water shortage in East Africa improving crop water use is vital especially in the arid and semi-arid regions of Ethiopia. To understand the response of barley to water and to simulate the biomass and grain yield of barley under various water inputs and planting dates, we tested the FAO AquaCrop model versions 3.0 using independent data sets during the cropping seasons of 2006, 2008 and 2009 at Mekelle site in northern Ethiopia. We found that the model is valid to simulate the barley biomass and grain yield under various planting dates in the study site. AquaCrop model can be used in the evaluation of optimal planting time. Out of the tested planting dates, planting on July 4 (early sowing) was found to maximize barley biomass, grain and water use efficiency. The model can also be used in the evaluation of irrigation strategies. Barley showed slightly lower performance under mild water stress condition compared to full irrigation condition. However, the model has indicated the possibility of obtaining more biomass and grain yield from a relatively larger barley field under (deficit irrigation) mild stress condition.     

Studies on the nitrogen and water relations of wheat II. Effects of varying nitrogen and water supply on growth and grain yield

Summary Wheat was grown in field and glasshouse experiments to assess the effect of nitrogen fertilizer on yield when water stress occurred in the later half of the growth. N application was deferred until the main culm apex of the plant was at the double-ridge stage of development. In the glasshouse water stress was imposed by altering the watering regime; in the field it was anticipated as naturally occurring and compared to an irrigated control. The response to deferred N was much stronger at adequate water supply giving rise to a significant positive N X W interaction effect. This positive N X W interaction was shown by number of ears, leaf area index, green area duration, water use and root growth, as well as grain yield. In both the glasshouse and field, N increased post-anthesis green area duration (PGD) which was highly correlated with grain yield, but since the components of grain yield determining the response to N were largely established by anthesis (number of ears), PGD does not appear to increase grain yield, which was rather caused by increased survival of tillers. In concert with its effect on PGD, deferred N resulted in greater root survival and/or growth at deeper layers late in the season. Water stress as measured in these experiments was insufficient to cause decreases in yield from use of N at low water supply. However, in the field nitrogen application did lower plant water potential late in the growing season.     

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.     

控释氮肥施用方式及用量对玉米干物质积累及子粒产量的影响

在大田条件下以不施氮为对照,采用随机区组设计了5个施氮水平,研究了控释氮肥施用方式及用量对玉米干物质积累、叶面积指数及子粒产量的影响。结果表明:施氮量在0~150 kg/hm2范围内,玉米干物质量、叶面积指数均表现为随施氮量的增加而增加,施用控释尿素处理玉米的干物质量、叶面积指数大口期前低于常规尿素处理,花后却显著高于常规尿素处理。该试验条件下,上述指标和施氮量均呈正相关关系。研究还表明,施氮量在0~150 kg/hm2范围内,玉米子粒产量随施氮量的增加而显著增加,增幅为5.0%~21.4%。施氮量为75 kg/hm2时,控释尿素底施、侧施比常规尿素分别提高6.7%和3.4%;施氮量增至150 kg/hm2时,控释尿素底施、侧施比常规尿素分别提高8.8%和1.9%。与常规尿素相比,控释尿素能更好地协调玉米的地上部生长,具有明显的“前控后保”效果,利于获得高产,而底施则可以显著提高这种效果。      

Modeling biomass, nitrogen and water dynamics in rice-wheat rotations

Rice-wheat cropping systems occupy between 24 and 26 Mha in Asia. A main feature of RW rotations is the alternation of aerobic and anaerobic soil conditions. This alternation of flooded and non-flooded soil conditions is conducive to N emissions, especially with the current high N rates in RW systems. To design alternative management systems, better understanding of the processes underlying emissions is required. For that purpose, the RIce WhEat Rotation model (RIWER) was developed, on the basis of existing crop, water and soil organic matter models, describing the relevant soil processes under both anaerobic and aerobic conditions. RIWER is evaluated using data from RW experiments in China. Assessment of model performance, on the basis of graphical comparison and goodness-of-fit parameters, showed that RIWER performs well in simulating total aboveground biomass, N uptake of cops and soil inorganic N content. The RIWER modeling framework needs further testing, but offers a promising operational tool to support the design of sustainable RW systems, combining environmentally-friendly production methods and high yields.     

Different indices to characterize water use pattern of micro-sprinkler irrigated onion (Allium cepa L.)

The amount of water used by any crop largely depends on the extent to which the soil water depletion from the root zone is being recharged by appropriate depth of irrigation. To test this hypothesis a field study was carried out in November–March of 2002–2003 and 2003–2004 on a sandy loam (Aeric haplaquept) to quantify the effect of depth of irrigation applied through micro-sprinklers on onion (Allium cepa L.) bulb yield (BY) and water use patterns. Seven irrigation treatments consisted of six amounts of sprinkler applied water relative to compensate crop (K_c) and pan (K_p) coefficient-based predicted evapotranspiration loss from crop field (ET_p) (i) 160% of ET_p (1.6ET_p); (ii) 1.4ET_p; (iii) 1.2ET_p; (iv) 1.0ET_p; (v) 0.8ET_p; (vi) 0.6ET_p; (vii) 40 mm of surface applied water whenever cumulative pan evaporation equals to 33 mm. Water use efficiency (WUE), net evapotranspiration efficiency (WUE_ET) and irrigation water use efficiency (WUE_I) were computed. Marginal water use efficiency (MWUE) and elasticity of water productivity (EWP) of onion were calculated using the relationship between BY and measured actual evapotranspiration (ET_c). Yield increased with increasing sprinkler-applied water from 0.6 to 1.4ET_p. Relative to the yield obtained at 0.6ET_p, yield at 1.0ET_p increased by 23–25% while at 1.4ET_p it was only 3–9% greater than that at 1.0ET_p. In contrast, yield at 1.6ET_p was 9–12% less than that at 1.4ET_p. Maximum WUE (7.21 kg m⁻³) and WUE_ET (13.87 kg m⁻³) were obtained under 1.0ET_p. However, the highest WUE_I (3.83 kg m⁻³) was obtained with 1.2ET_p. The ET_c associated with the highest WUE was 20% less than that required to obtain the highest yields. This study confirmed that critical levels of ET_c needed to obtain maximum BYs, or WUE, could be obtained more precisely from the knowledge of MWUE and EWP.     

Effect of irrigation amounts applied with subsurface drip irrigation on corn evapotranspiration, yield, water use efficiency, and dry matter production in a semiarid climate

Quantifying the local crop response to irrigation is important for establishing adequate irrigation management strategies. This study evaluated the effect of irrigation applied with subsurface drip irrigation on field corn (Zea mays L.) evapotranspiration (ETc), yield, water use efficiencies (WUE = yield/ETc, and IWUE = yield/irrigation), and dry matter production in the semiarid climate of west central Nebraska. Eight treatments were imposed with irrigation amounts ranging from 53 to 356 mm in 2005 and from 22 to 226 mm in 2006. A soil water balance approach (based on FAO-56) was used to estimate daily soil water and ETc. Treatments resulted in seasonal ETc of 580–663 mm and 466–656 mm in 2005 and 2006, respectively. Yields among treatments differed by as much as 22% in 2005 and 52% in 2006. In both seasons, irrigation significantly affected yields, which increased with irrigation up to a point where irrigation became excessive. Distinct relationships were obtained each season. Yields increased linearly with seasonal ETc (R² = 0.89) and ETc/ETp (R² = 0.87) (ETp = ETc with no water stress). The yield response factor (ky), which indicates the relative reduction in yield to relative reduction in ETc, averaged 1.58 over the two seasons. WUE increased non-linearly with seasonal ETc and with yield. WUE was more sensitive to irrigation during the drier 2006 season, compared with 2005. Both seasons, IWUE decreased sharply with irrigation. Irrigation significantly affected dry matter production and partitioning into the different plant components (grain, cob, and stover). On average, the grain accounted for the majority of the above-ground plant dry mass (≈59%), followed by the stover (≈33%) and the cob (≈8%). The dry mass of the plant and that of each plant component tended to increase with seasonal ETc. The good relationships obtained in the study between crop performance indicators and seasonal ETc demonstrate that accurate estimates of ETc on a daily and seasonal basis can be valuable for making tactical in-season irrigation management decisions and for strategic irrigation planning and management.     

Simulating water content, crop yield and nitrate-N loss under free and controlled tile drainage with subsurface irrigation using the DSSAT model

In southwestern Ontario, rain-fed crop production frequently fails to achieve its yield potential because of growing-season droughts and/or uneven rainfall distribution. The objective of this study was to determine if the Decision Support System for Agrotechnology Transfer (DSSAT) v4.5 model could adequately simulate corn and soybean yields, near-surface soil water contents, and cumulative nitrate-N losses associated with regular free tile drainage (TD) and controlled tile drainage with optional subsurface irrigation (CDS). The simulations were compared to observations collected between 2000 and 2004 from both TD and CDS field experiments on a Perth clay loam soil at the Essex Region Conservation Authority demonstration farm, Holiday Beach, Ontario, Canada. There was good model-data agreement for crop yields, near-surface (0-30 cm) soil water content and cumulative annual tile nitrate-N loss in both the calibration and validation years. For both TD and CDS, the CENTURY soil C/N model in DSSAT simulated water content and cumulative tile nitrate-N loss with normalized root mean square error (n-RMSE) values ranging from 9.9 to 14.8% and 17.8 to 25.2%, respectively. The CERES-Maize and CROPGRO-Soybean crop system models in the DSSAT simulated corn and soybean yields with n-RMSE values ranging from 4.3 to 14.0%. It was concluded that the DSSAT v4.5 model can be a useful tool for simulating near-surface soil water content, cumulative tile nitrate-N losses, and corn and soybean yields associated with CDS and TD water management systems.     

不同生育期干旱胁迫对玉米籽粒灌浆及产量的影响

为研究不同生育期干旱胁迫对玉米籽粒灌浆及产量的影响,分别设置正常水分、拔节期干旱、抽雄期干旱和灌浆初期干旱4个处理,研究玉米干物质积累、灌浆特性、淀粉相关酶活性及产量的变化特征。结果表明:干旱显著降低玉米干物质积累量,抽雄期和灌浆初期干旱显著降低花后干物质积累量和贡献率;干旱显著降低籽粒质量和灌浆速率,抽雄期干旱对后期籽粒质量和灌浆速率影响最大;干旱显著降低结合态淀粉合成酶（GBSS）、可溶性淀粉合成酶（SSS）、蔗糖合成酶（SS）和蔗糖磷酸合成酶（SPS）活性;干旱对产量的影响主要是增加了秃尖长、减少了行粒数,3个时期干旱胁迫产量分别降低15.15%、33.11%和22.00%。因此,拔节期、抽雄期和灌浆初期玉米对水分的需求较为敏感,对产量影响较大,尤其是在玉米抽雄期,要确保水分供应,以保证玉米产量。      

The viability of irrigating mandarin trees with saline reclaimed water in a semi-arid Mediterranean region: a preliminary assessment

The effect of irrigation water quality was investigated in a commercial mandarin orchard during four growing seasons using fresh water (EC ≈ 1 dS m^?1), irrigators’ association water (EC = 1–3 dS m^?1) and reclaimed water (RW) (EC ≈ 3 dS m^?1). RW had higher concentration of macro- and micronutrients, especially potassium, and the phytotoxic elements, boron, sodium and chlorides. The microbiological load in the different irrigation water sources showed a high seasonal variability, and all water sources occasionally exceeded health standards to irrigate fruit trees. In the RW treatment, an increase in soil salinity and leaf boron concentration was observed. The nutritional contribution of RW was high, providing 24 and 15 % of the annual nitrogen and phosphorus (N and P₂O₅) fertilizer requirement for mandarin oranges, respectively, and RW treatment satisfied the entire potassium requirement (K₂O). An important fluctuation in the crop production was observed during the 4 years in the different water quality treatments. In general, quality parameters of mandarins were not affected. The results provide additional evidence that long-term effects must be studied to test sustainability when using RW irrigation on fruit trees.     

The impact of agriculture on ground water quality in Slovenia: standards and strategy

Ground water and water from springs are sources used for water supply in Slovenia. The quality of these waters has been monitored since 1987. Among 12 main ground water aquifers in Slovenia the amount of nitrate exceeds the allowable level (50 mg/l) for drinking water in areas with more intensive agricultural production with higher concentrations of animals (two livestock unit – LU/ha) and where drainage of sewage water is not excellently arranged or where quality of river water that effluent ground water is not well. The identification of nitrogen surpluses has been done on regional and farm level (using normative approach). This method is taking into account nitrogen input from mineral fertiliser, animal wastes and the deposition from the atmosphere minus nitrogen uptake of harvested crops and ammonia losses to the atmosphere. On an average nitrogen input from mineral fertiliser is low, while input from organic manure is rather high – 90 kg/ha. Average net-balance surplus for Slovenia is about 56 kg N/ha. The differences between regions are relatively high. In the most intensive arable region with high intensity of animal husbandry (2 LU/ha) nitrogen surplus is about 90 kg/ha. This region can be identified as vulnerable for nitrogen leaching into ground water. In regions with limited growing conditions for agriculture plants (climate, soil depth) just small increase of livestock density can cause high nitrogen surpluses. Our Slovenian legislation, which almost entirely corresponds to EC Nitrate Directive and Code of Good Agricultural Practice intends to reduce mineral surpluses in agriculture and meet the standards of nitrate in drinking water.     

Timing of limited irrigation and N-injection for grain sorghum

When subsurface irrigation sources are lacking in humid and subhumid regions, high yearly precipitation may allow for storage of surface water in farm ponds and lakes for irrigation. Irrigation at selected growth stages may avoid critical stress for crops with some drought tolerance, such as grain sorghum [Sorghum bicolor (L.) Moench]. Because grain sorghum is responsive to N, injecting fertilizer N through the irrigation system also may improve production. The objective of this study was to determine the effect of timing of limited-amount irrigation and N fertigation on grain sorghum yield; yield components; grain N content; and N uptake at the 9-leaf, boot, and soft dough stages. The experiment was conducted from 1984 to 1986 on a Parsons silt loam (fine, mixed, thermic, Mollic Albaqualf). The experiment was designed as a 6 × 2 factorial plus two reference treatments. Six timings for irrigation were targeted at the 9-leaf (9L), boot (B), soft dough (SD), 9L-B, 9L-SD, and B-SD growth stages. N application systems were either 112 kg N ha^–1 surface-banded preplant or 56 kg N ha^-1 preplant and 56 kg N ha^–1 injected through the irrigation at a rate of 28 kg N ha^–1 per 2.5 cm of irrigation. Two reference treatments included were one receiving N but no irrigation and one receiving neither N nor irrigation. In 1984, irrigation generally increased grain sorghum yield by nearly 1 Mg ha^–1. However, yield was not affected by selection of irrigation timing, N application method, or the interaction of the two factors. This was partly because early irrigations increased kernels/head, whereas later irrigations increased kernel weight. Above average rainfall during the growing season, especially just prior to the 9-leaf, boot, and soft dough growth stages, resulted in no irrigations in 1985. In 1986, yield was increased by early (9-leaf) irrigations as compared to soft dough irrigations. Early irrigations resulted in higher kernels/head; however, rainfall after the soft dough irrigation may have masked any treatment effect on kernel weight. As in 1984, N application method did not affect grain sorghum yields, even though yield was reduced to less than 3 Mg ha^–1 with no N nor irrigation. In both 1984 and 1986, N uptake at succeeding growth stages appeared to respond to irrigations made at previous growth stages. Injecting half of the fertilizer N through the irrigation system did not affect N uptake compared to applying all N preplant. The lack of response to fertigation may be related to the low leaching potential of the soil used in this study.Contribution No. 92-606-J, Kansas Agricultural Experiment Station     

Evaluating deficit irrigation management strategies for grain sorghum using AquaCrop

Many wells in the US Central Plains can no longer meet full crop water requirements due to declines in Ogallala aquifer water levels. A study was conducted in Southwest Kansas to determine optimum limited irrigation strategies for grain sorghum. Objectives were to (1) calibrate and validate the AquaCrop model, (2) apply AquaCrop to assess the effect of varying climate, planting dates, and soil types on yield, and (3) evaluate water productivities and optimal irrigation needs. Experimental data of grain sorghum were used to calibrate and validate AquaCrop. Planting date was found to substantially affect biomass and grain yield, and hence, considerably affect water productivities. The highest grain water productivities were obtained with late planting in a wet season. Late planting was associated with lower irrigation requirements. Depending on local conditions, we recommend planting to occur between June 1st and June 10th. Grain sorghum yield was optimized on sandy soils of southwestern Kansas with irrigation of 100–275 mm for early, 150–275 mm for normal and 100–275 mm for late planting. The optimal irrigation on silt loam soils for the corresponding planting dates were 175–350, 175–250 and 125–250 mm, respectively, with the lowest and highest in the range being for the wet and dry climate season conditions. Fluctuations in grain sorghum prices had a substantial impact on economic water productivity. Overall planting grain sorghum under optimum conditions combined with deficit irrigation improved water productivity.