亏缺灌溉对风沙区春小麦生长发育及水分生产效率的影响

20 0 1年在内蒙风沙区对春小麦进行了各生育阶段不同程度亏缺灌溉的试验研究 ,结果表明 :春小麦不同生长时期、不同程度的水分亏缺对其生长发育、产量构成及水分生产效率会产生不同的影响。拔节—孕穗期受旱对株高、叶面积、穗粒数影响最大 ,减产最多 ,其次是抽穗—开花期干旱 ;灌浆成熟期受旱主要影响千粒重。在同一生育阶段 ,水分亏缺越严重 ,春小麦受害越深。在春小麦生长前期适度的水分胁迫不但对产量无显著影响 ,反而有利于提高水分生产效率     

Maize yield response to deficit irrigation during low-sensitive growth stages and nitrogen rate under semi-arid climatic conditions

Knowledge of crop production in suboptimal environmental conditions not only helps to sustain crop production but also aids in the design of low-input systems. The objective of this study was to evaluate the effects of water stress imposed at low-sensitive growth stages (vegetative, reproductive, and both vegetative and reproductive) and level of nitrogen (N) supply (100 and 200 kg ha⁻¹) on the physiological and agronomic characteristics of two hybrids of maize (Zea mays L.). A two-site field experiment was carried out using a randomized complete block design with three replications and a split-factorial arrangement. A water deficit (WD) was induced by withholding irrigation at different stages of crop development. The results showed that proline content increased and the relative water content, leaf greenness, 100-kernel weight and grain yield decreased under conditions of WD. The highest IWUE was obtained when maize endured WD at vegetative stage at two sites. The limited irrigation imposed on maize during reproductive stage resulted in more yield reduction than that during vegetative stage, compared with fully irrigated treatment. The 100-kernel weight was the most sensitive yield component to determine the yield variation in maize plant when the WD treatments were imposed in low-sensitive growth stages. The results of the statistical regression analysis showed liner relationships between RGR during a period bracketing the V₈ or R₃ stages and 100-kernel weight in all the WD treatments. The increase of N supply improved yield and IWUE when maize plant endured once irrigation shortage at vegetative stage. But, the performance of high N fertilizer reduced and eliminated when water deficit imposed once at reproductive stage and twice at vegetative and reproductive stages, respectively. Furthermore, the response of T.C647 hybrid to increase of N supply was stronger than S.C647 hybrid.     

Salinity sensitivity of sorghum at three growth stages

Summary The relative salt tolerance of two sorghum cultivars [Sorghum bicolor (L.) Moench., cvs. Northrup King 265 and Asgrow Double TX] at three different stages of growth was determined in a greenhouse experiment. Plants were grown in sand cultures irrigated four times daily with modified Hoagland's solution. A nonsaline solution and six solutions salinized with NaCl and CaCl₂ (2: 1 molar ratio) provided treatments with osmotic potentials (_s) ranging from –0.05 to –1.05 MPa. The saline treatments were imposed for 30 days beginning at either Stage 1, 4, or 7 as defined by Vanderlip and Reeves (Agron J. 64:13, 1972). The 30-day stages are referred to here as the vegetative, reproductive and maturation stages although the first stage may have included initial panicle differentiation. Both cultivars were most sensitive to salinity during the vegetative stage and least sensitive during maturation. Based on a nonlinear least-squares analysis, grain yield reductions of 50% were predicted at _s=–0.68, –1.02, and –1.14 MPa for NK265 and at –0.62, –1.00, and –1.10 MPa for Double TX when salinized during the vegetative, reproductive, and maturation stages, respectively. Although salinity had no significant effect on mean kernel weights, significant growth stage effects and interaction indicated that kernels were heaviest for plants salinized during the vegetative stage. Stover yields were significantly reduced by salination during the vegetative stage but were unaffected when plants were salinized during the maturation stage. Salination during the reproductive stage also decreased stover yield of Double TX but the effect was smaller than that during the first stage. Stover yield of NK265 was unaffected by salinity at this stage.Mineral analysis of the first leaf below the flag leaf at harvest indicated that both cultivars tended to exclude Na from the upper leaves. Ca and Cl concentrations increased with increased salinity in plants salinized during the maturation stage but salination in earlier stages decreased Ca concentration of this upper leaf at harvest and had no effect on the final Cl concentration. Phosphate and K concentrations decreased when plants were salinized during the third stage but increased when plants were salinized during the vegetative and reproductive stages. Mg was unaffected by salinization during the first and last stage but decreased when plants were salinized,during the reproductive stage. An extensive data base now exists which describes the salt tolerances of many different crops (Maas and Hoffman 1977; Maas 1986). These data express yield responses as a function of the average salt concentration in the rootzone. Generally, these data apply only if salinity is fairly uniform from the seedling stage to maturity. Except for germination, little information exists on the tolerances of crops at different stages of growth. Such information could be invaluable to optimize the use of limited water resources. Knowledge that crops are more tolerant during some stages of growth will improve new strategies for utilizing saline drainage waters (Rhoades 1984).Several studies indicate that tolerances do change as the crop develops and matures, but none of these studies completely separated the effects of duration of treatment from the stage of growth that the crop was treated (Ayers et al. 1952; Kaddah and Ghowail 1964; Kovalskaia 1958; Lunin et al. 1961 a, 1961 b; Maas et al. 1983; Ogo and Sasai 1955; Piruzyan 1959; Verma and Bains 1974). Comparisons of sensitivity during specific phenological stages are confounded when treatment periods are of unequal duration.This study was initiated to determine the sensitivity of grain sorghum [Sorghum bicolor (L.) Moench] to salinity during three 30-day periods of growth. Francois et al. (1984) recently reported that sorghum is a moderately salt-tolerant crop. In field plot tests, grain yields of two cultivars decreased 16% per unit increase in salinity (electrical conductivity of saturated soil extracts from the rootzone) above 6.8 dS/m. They further reported that both cultivars were significantly more tolerant at germination than at later stages of growth. Soil water salinities above 8.2 dS/m delayed germination but full germination occurred within 10 days at salinities up to 22 dS/m. Treatments in the present study were designed to assess plant growth and yield responses to 30-day exposures to salinity beginning at either the 2-leaf stage, at the beginning of rapid culm elongation, or after anthesis.     

Yield performance of spring wheat improved by regulated deficit irrigation in an arid area

A field experiment was conducted in 2003 and 2004 growing seasons to evaluate the effects of regulated deficit irrigation on yield performance in spring wheat (Triticum aestivum) in an arid area. Three regulated deficit irrigation treatments designed to subject the crops to various degrees of soil water deficit at different stages of crop development and a no-soil-water-deficit control was established. Soil moisture was measured gravimetrically in the increment of 0–20 cm every five to seven days in the given growth periods, while that in 20 increments to 40, 40–60, 60–80, and 80–100 cm depth measured by neutron probe. Compared to the no-soil-water-deficit treatment, grain yield, biomass, harvest index, water use efficiency (WUE), and water supply use efficiency (WsUE) in spring wheat were all greatly improved by 16.6–25.0, 12.4–19.2, 23.5–27.3, 32.7–39.9, and 44.6–58.8% under regulated deficit irrigation, and better yield components such as thousand-grain weight, grain weight per spike, number of grain, length of spike, and fertile spikelet number were also obtained, but irrigation water was substantially decreased by 14.0–22.9%. The patterns of soil moisture were similar in the regulated deficit treatments, and the soil moisture contents were greatly decreased by regulated deficit irrigation during wheat growing seasons. Significant differences were found between the no-soil-water-deficit treatment and the regulated soil water deficit treatments in grain yield, yield components, biomass, harvest index, WUE, and WsUE, but no significant differences occurred within the regulated soil water deficit treatments. Yield performance proved that regulated deficit irrigation treatment subjected to medium soil water deficit both during the middle vegetative stage (jointing) and the late reproductive stages (filling and maturity or filling) while subjected to no-soil-water-deficit both during the late vegetative stage (booting) and the early reproductive stage (heading) (MNNM) had the highest yield increase of 25.0 and 14.0% of significant water-saving, therefore, the optimum controlled soil water deficit levels in this study should range 50–60% of field water capacity (FWC) at the middle vegetative growth period (jointing), and 65–70% of FWC at both of the late vegetative period (booting) and early reproductive period (heading) followed by 50–60% of FWC at the late reproductive periods (the end of filling or filling and maturity) in treatment MNNM, with the corresponding optimum total irrigation water of 338 mm. In addition, the relationships among grain yield, biomass, and harvest index, the relationship between grain yield and WUE, WsUE, and the relationship between harvest index and WUE, WsUE under regulated deficit irrigation were also estimated through linear or non-linear regression models, which indicate that the highest grain yield was associated with the maximum biomass, harvest index, and water supply use efficiency, but not with the highest water use efficiency, which was reached by appropriate controlling soil moisture content and water consumption. The relations also indicate that the harvest index was associated with the maximum biomass and water supply use efficiency, but not with the highest water use efficiency.     

气候变化条件下旱作玉米用水效率与单产变化趋势分析

以渭北旱塬合阳和长武2个试验站点为研究区域,通过多年的玉米田间试验数据评估CERES-Maize模型的适用性,再利用区域气候模式Reg CM4.0输出的气象数据对2050年前玉米单产及生产水足迹进行预测。结果表明:CERES-Maize模型可以很好地模拟雨养玉米产量和物候期,多数年份二者的绝对相对误差(Absolute relative error,ARE)在10%以内,CERES-Maize模型在渭北旱塬旱作农业区有很好的适用性。应用CERES-Maize模型模拟玉米生产水足迹,较传统水足迹计算方法得到的结果更为精确可靠。在RCP2.6气候情景下,随着温度升高和生育期有效降水量的增加,玉米产量呈上升趋势;在RCP8.5气候情景下,随着温度升高和生育期有效降水的减少,玉米产量呈下降趋势。气温上升幅度过大对玉米单产有明显的负面影响,降水与玉米用水效率呈正相关。为有效应对气候变化对旱作作物产量造成的负面影响,应采取减少温室气体排放量、增强土壤蓄水保墒能力、发展集雨补灌、筛选和培育节水抗旱新品种等措施。     

The influence of bearing cycles on olive oil production response to irrigation

Water requirements for olive oil production and the effects of deficit irrigation were determined while considering the relative fruit loads on trees occurring as a result of biennial bearing cycles. Two Israeli olive (Olea europaea) varieties (Barnea and Souri) were evaluated for growth and yield parameters in a 4-year field study where five relative irrigation rates were applied. Increasing irrigation increased stem water potential, vegetative growth, and olive fruit yield with the increases tapering off at application rates reaching 75–100% of potential crop evapotranspiration. Tree water status, growth, and fruit characteristic parameters were highly affected by both fruit load and by irrigation level. Oil yield increases as a function of increased irrigation were initiated for each cultivar only following an ‘off’ season when the treatments lead to higher vegetative growth. The increased oil yields as a function of increased irrigation were primarily explained by higher tree-scale capacity for carrying fruit, especially as irrigation alleviated measureable water stress. For the Barnea cultivar in ‘on’ years, a secondary effect due to increased oil per fruit as irrigation increased was evident, particularly at the higher application rates.     

Effects of deficit irrigation scheduling on yields and soil water balance of irrigated maize

This paper presents the findings of the effect of some selected deficit irrigation scheduling practices on irrigated maize crop in a sub-catchment in south western part of Tanzania. Field experiments, in which maize (TMV1-ST) variety was planted under total irrigation, were conducted during the dry seasons of 2004 and 2005. Surface irrigation method was used and the crop was planted in basins. The seasonal water applied ranged from 400 to 750 mm. Soil moisture content from both cropped and bare soils, leaf area index, dry matter, and grain yields were measured. The dry matter yield ranged between 6,966 and 12,672 kg/ha, and grain yields obtained were between 1,625 and 4,349 kg/ha. The results showed that deficit irrigation at any crop growth stage of the maize crop led to decrease in dry matter and grain yields, seasonal evapotranspiration and deep percolation. Deficit irrigation in any one growth stage of the maize crop only seems to affect grain production and no significant effect on biomass production, but deficit irrigation that spanned across two or more growth stages affect both biomass and grain production drastically. Crop water use efficiency (WUE) and Irrigation water use efficiency (IWUE) were strongly influenced by the number of growth stages in which deficit irrigations were applied and how critical the growth stages were to moisture stress rather than the amount of irrigation water applied. While maximum WUE was obtained under full irrigation, maximum IWUE was obtained in the deficit irrigation treatment at vegetative growth stage, which suggest that IWUE may be improved upon by practicing deficit irrigation at the vegetative growth stage of the maize crop.     

Early sowing and irrigation to increase barley yields and water use efficiency in Mediterranean conditions

In rainfed Mediterranean areas, early sowings which lead to early growth and maturity to escape terminal heat and drought usually give higher grain yield than late sowings in years when rains come early. We test the hypothesis that early sowing coupled with a small amount of irrigation to ensure earlier emergence increases grain yield significantly, while improving irrigation water productivity. Replicated field experiments were conducted for 4 years in the semi-arid central Bekaa Valley of Lebanon. Barley was sown early, and half of the plots were irrigated with 25-30 mm of water immediately after sowing (EI). Half of the plots also received irrigation around heading stage (LI). Besides yields, other agronomic data were collected throughout crop growth, and the supplemental irrigation water use efficiency (WUE_SI) was calculated. Our results confirm the hypothesis that in Mediterranean areas early sowing followed immediately with a small amount of irrigation increases barley grain yield significantly. Farmers in the region should seriously consider practicing this technique as it produces a higher WUE_SI than irrigation at the heading stage.     

Deficit irrigation in maize for reducing agricultural water use in a Mediterranean environment

Research on crop response to deficit irrigation is important to reduce agricultural water use in areas where water is a limited resource. Two field experiments were conducted on a loam soil in northeast Spain to characterize the response of maize (Zea mays L.) to deficit irrigation under surface irrigation. The growing season was divided into three phases: vegetative, flowering and grain filling. The irrigation treatments consisted of all possible combinations of full irrigation or limited irrigation in the three phases. Limited irrigation was applied by increasing the interval between irrigations. Soil water status, crop growth, above-ground biomass, yield and its components were measured. Results showed that flowering was the most sensitive stage to water deficit, with reductions in biomass, yield and harvest index. Average grain yield of treatments with deficit irrigation around flowering (691 g m⁻²) was significantly lower than that of the well-irrigated treatments (1069 g m⁽²). Yield reduction was mainly due to a lower number of grains per square metre. Deficit irrigation or higher interval between irrigations during the grain filling phase did not significantly affect crop growth and yield. It was possible to maintain relatively high yields in maize if small water deficits caused by increasing the interval between irrigations were limited to periods other than the flowering stage. Irrigation water use efficiency (IWUE) was higher in treatments fully irrigated around flowering.     

Effects of irrigation regimes on yield and water productivity of safflower (Carthamus tinctorius L.) under Mediterranean climatic conditions

A field study was carried out in order to determine the effect of deficit irrigation regimes on grain yield and seasonal evapotranspiration of safflower (Carthamus tinctorius L.) in Thrace Region of Turkey. The field trials were conducted on a loam Entisol soil, on Dincer, the most popular variety in the research area. A randomised complete block design with three replications was used. Combination of four well-known growth stages of the plant, namely vegetative (V_a), late vegetative (V_b), flowering (F) and yield formation (Y) were considered to form a total of 16 (including rain fed) irrigation treatments. The effect of irrigation and water stress at any stage of development on grain yield per hectare and 1000 kernels weight was evaluated. Results showed that safflower was significantly affected by water stress during the sensitive late vegetative stage. The highest yield was obtained in V_aV_bFY treatment. Seasonal irrigation water use and evapotranspiration were 501 and 721 mm, respectively, for the non-stressed treatment. Safflower grain yield of this treatment was 5.22 Mg ha⁻¹ and weight of 1000 kernels was 55 g. The seasonal yield-water response factor value was 0.87. The total water use efficiency was 7.2 kg ha⁻¹ mm⁻¹. Irrigation schedule of the non-stressed treatment may be as follows: the first irrigation is at the vegetative stage, when after 40-50 days from sowing/elongation and branching stage, that is the end of May; the second irrigation is at the late vegetative stage, after 70-80 days from sowing/heading stage, that is in the middle of June; the third irrigation is at the flowering stage, approximately 50% level, that is the first half of July; and the fourth irrigation is at the yield formation stage, seed filling, that is the last week of July.     

土壤空间变异对水氮淋失和产量影响的模拟研究

基于CERES-Maize模型,研究了土壤空间变异和水文年型对半干旱地区土壤水氮淋失和玉米产量的影响.结果表明,土壤空间变异对作物产量和土壤水氮淋失的影响程度与降雨密切相关.丰水年水氮淋失量显著高于平水年和枯水年.降雨对作物产量和农田尺度水氮淋失的空间变异有明显影响,并能在一定程度上减弱土壤空间变异对产量和农田尺度水氮淋失的影响.随着土壤空间变异程度的增大,产量降低,产量的空间变异程度增加.水分渗漏和氮淋失量随土壤空间变异的增加呈增加趋势.当土壤黏粒和粉粒含量变异系数CV≥0.2时,在水氮管理中考虑土壤空间变异有利于提高作物产量,减轻水氮淋失.     

棉瓜间作条件下水分调控对棉花生育及水分生产效益的影响

以黄淮区种植面积相对较大的棉、瓜间作模式为研究对象,开展了不同生育阶段水分亏缺对棉花的生长发育、产量及水分生产效益的影响研究,确定棉、瓜间作的适宜土壤水分控制指标。结果表明,苗期适度亏水对棉花生育和棉、瓜产量的影响较小,节水效果较明显;蕾期缺水对棉花影响较少,节水效果最明显,但对甜瓜产量影响最大;花铃前期不同程度水分亏缺的成铃数低于其他处理且脱落率较高,棉、瓜减产幅度均较大,为棉、瓜需水关键期;花铃后期缺水仍会导致蕾铃脱落率增加,不利于产量的进一步提高。综合比较各项指标,大田棉、瓜间作高产高效的土壤水分适宜控制下限指标为:苗期土壤含水率不低于田间持水率(FC)50%,蕾期为60%FC～65%FC,花铃前期为75%FC～80%FC,花铃后期为70%FC～75%FC。     

地下水埋深对玉米生长发育及水分利用的影响

为研究地下水埋深对作物的生长发育及水分利用的影响,选择具有代表性的夏玉米为研究对象,借助地中渗透仪,通过人工控制设置不同地下水埋深（分别设置0.2,0.4,0.6,0.8,1.0和1.2 m）,探讨地下水埋深对不同生育期夏玉米的形态指标、产量、耗水量及地下水补给量的影响,分析不同地下水埋深条件下水分利用率差异.结果表明：地下水埋深对玉米株高的影响不具有统计学意义,而地下水埋深过浅或过深均会明显抑制植株叶面积指数和茎粗的增长（P〈0.05）,地下水埋深0.4 m时叶面积指数和茎粗最大.随作物生育进程,根系数量和根系干质量随地下水埋深增大,先减小后增大.玉米灌浆前,单株根系伤流量随地下水埋深增大而增大,而灌浆前后则无显著影响.地下水位埋深过深或过浅均影响穗长、秃尖长、穗粒数、百粒质量及经济产量.分析表明,0.53 m为当地玉米产量最优地下水位埋深.玉米生长期内0~80 cm土层土壤含水量随着地下水埋深增大而降低,同一地下水埋深处理玉米生育期内土壤含水量变化幅度较小.夏玉米全生育期耗水量、阶段耗水量及耗水强度随地下水位埋深增大而直线减少,回归方程在P〈0.01水平下具有统计学意义;同样夏玉米全生育期地下水补给量、阶段地下水补给量及地下水补给强度随地下水位埋深增大而直线减少,回归方程在P〈0.01水平下也具有统计学意义.玉米水分利用率随地下水埋深增大而增大,地下水埋深1.2 m处理水分利用率最高.研究成果对江淮丘陵区地下水资源利用及评价、玉米高产高效灌溉制度的制订具有实际意义.     

Moisture stress in navy beans

Summary The effect of plant water stress imposed at all combinations of the three main phenological stages (preflower, flowering and pod development) on the yield and growth of Navy beans was studied in field experiments at the Inglewood irrigation area of Queensland during the summers of 1971 and 1972. In 1971, a short, mild growing season with early frosts, yields varied with treatment, from 0.55 to 1.52 t ha^–1, in 1972 a hotter growing season especially during the preflower stage but one of normal duration, yields varied from 1.12 to 2.27 t ha^–1. Moisture stress imposed in the preflower and flowering stages in 1971 reduced yields by 28% and 24% respectively. In 1972 moisture stress during the preflower stage reduced yield by 37% only if irrigation was also withheld during the flowering stage. Moisture stress imposed during the flowering stage in 1972 reduced yields by 40%. Evaluation of the effects of moisture stress during the pod development stage was not possible due to early frosts in 1971 and rainfall in 1972. Yields were almost equally highly correlated with leaf area index (r=0.82) and leaf area duration (r=0.84). Crop growth rate was similarly correlated with leaf area index (r=0.85).     

Effects of water stress at different development stages on yield and water productivity of winter and summer safflower (Carthamus tinctorius L.)

A field study was carried out to determine the effects of water stress imposed at different development stages on grain yield, seasonal evapotranspiration, crop-water relationships, yield response to water and water use efficiency of safflower (Carthamus tinctorius L.) for winter and summer sowing. The field trials were conducted on a loam Entisol soil in Thrace Region in Turkey, using Dincer, the most popular safflower variety in the research area. A randomised complete block design with three replications was used. Three known growth stages of the plant were considered and a total of 8 (including rainfed) irrigation treatments were applied. The effect of irrigation or water stress at any stage of development on grain yield per hectare and 1000 kernel weight, was evaluated. Results of this study showed that safflower was significantly affected by water shortage in the soil profile due to omitted irrigation during the sensitive vegetative stage. The highest yield was observed in the fully irrigated control and was higher for winter sowing than for summer sowing. Evapotranspiration calculated for non-stressed production was 728 and 673 mm for winter and summer sowing, respectively. Safflower grain yield of the fully irrigated treatments was 4.05 and 3.74 t ha⁻¹ for winter and summer season, respectively. The seasonal yield response factor was 0.97 and 0.81 for winter and summer sowing, respectively. The highest total water use efficiency was obtained in the treatment irrigated only at vegetative stage while the lowest value was observed when the crop was irrigated only at yield stage. As conclusions: (i) winter sowing is suggested; (ii) if deficit irrigation is to apply at only one or two stages, Y stage or Y and F stages should be omitted, respectively.     

分根区交替灌溉下水分亏缺对夏玉米生长和水分利用效率的影响

为探讨玉米节水灌溉方式的理论依据,通过桶栽试验研究了分根区交替灌溉(APRI)方式下,不同生育期水分亏缺对夏玉米生长、干物质累积质量、籽粒产量、总耗水量和水分利用效率(WUE)的影响.结果表明:常规灌溉(CI)方式下,苗期和全生育期水分亏缺的株高、叶面积和总耗水量均显著低于充分灌溉,但苗期水分亏缺可以提高WUE.相同的灌水方式和亏缺时期,中度亏缺的根干物质质量、地上和总干物质质量以及籽粒产量均显著高于重度亏缺;相同的灌水方式和灌水水平,苗期水分亏缺的株高、叶面积、根干物质质量、地上和总干物质质量以及总耗水量均显著的低于灌浆期,但籽粒产量和WUE均显著高于灌浆期;相同的灌水水平和亏缺时期,APRI的根干物质质量和总耗水量均显著低于CI的,但APRI的籽粒产量和水分利用效率均显著高于CI的.本研究结果表明,APRI在苗期进行中度亏缺有利于营养生长的调控,并达到节水高产,提高WUE的目的.     

Yield response of a semi-dwarf wheat variety to irrigation on a calcareous brown flood plain soil of Bangladesh

Field studies were conducted to determine the yield performance of a semi-dwarf high yielding variety of wheat (Triticum aestivum L., cv. ‘Sonalika’) in response to irrigation provided at various critical stages of growth. Determination of an irrigation schedule for most efficient water management was attempted. The study, conducted on a calcareous brown flood plain soil, comprised a randomized block design experiment with eight irrigation treatments applied at critical growth stages.The yield of wheat was the highest and the irrigation efficiency maximum, when two irrigations, totalling 9.5 cm, were given at tillering and booting stages. The quantity of irrigation water applied was calculated on the basis of deficit from field capacity level of soil water content. The lowest grain yields were obtained in treatments receiving either no irrigation or only one irrigation at the grain-filling stage. The percent increase over control (no irrigation) in grain yield, due to various irrigation treatments, ranged from 21 to 92%. The data revealed that the depletion of soil water increased as the amount of irrigation water increased.The results indicate that the present yield levels of wheat in Bangladesh can easily be increased by 50–100% by irrigating with only one-third to one-half of the water currently being used, provided it is scheduled and managed efficiently, keeping in view the need of the crops as well as the soils.     

Mungbean response to surface drainage when grown as a pre-rice crop on waterlog-prone ricelands

Large areas of the world's bunded rainfed lowland ricelands could be planted to a pre-rice crop if waterlogging damage during the early wet season is prevented. To build understanding necessary to develop effective field drainage practices for pre-rice crops, pot and field studies were undertaken on a Typic Tropaquept lowland rice soil in the Cagayan Valley, Philippines. The objective of the studies was to quantify effects of excessive moisture on mungbeans (Vigna radiata (L.) Wilczek) encountering variable regimes of duration and elevation of water table height in the root zone during a shortterm waterlogging event. Small differences in level and duration of the root zone water table markedly affected plant performance. Yields were reduced by 40–100% when the water table level reached the soil surface for 6 days compared with the unstressed treatment, but were reduced by only 12–17% when the water level was 5 cm below the surface for the same time period. Regression analysis revealed a 4% reduction in yield per centimetre increase in water table level between 5 cm below to 5 cm above the soil surface during the vegetative stage, and a 6.5% reduction per centimetre during the reproductive stage. Field experiments evaluated two prospective surface drainage techniques that farmers could employ to elevate the crop above the zone of saturation during waterlogging events. Planting in furrows, and subsequently hilling up (HU) to create ridges was unsuccessful in improving plant performance (as the base of the plant was not elevated). Planting on 25 cm high ridges formed by a plow dramatically improved growth and yield of mungbean ( ≥ 360% advantage compared with the other treatments) when subjected to a range of waterlogging stress events. Standing water occurred for 5–7 days on the soil surface of HU, broadcast seeded (B), and drilled (D) treatments, but was 56 6 cbelow the base of the plants in the ridge treatment during the two flooding events. The ridging method was observed to be effective for farm-scale use in cultivating pre-rice mungbeans with either animal or tractor power.     

Large-scale simulation of wheat yields in a semi-arid environment using a crop-growth model

The ability to predict wheat yields from large-scale weather variables has benefits throughout the semi-arid regions of the world. In spite of the availability of numerous crop-growth models, there has been little concerted effort to analyse yields regularly at spatial scales that are relevant to agronomic decision makers. As a result many current crop-growth models are research tools only. A large-scale wheat yield assessment procedure, based on the CERES Wheat model, has been developed for the semi-arid climate of Saskatchewan. It is suitable for simulating yields at the crop-district level, an area of about 2 million hectares containing several hundred farms having different soils, climates and management practices. Simulations of spring wheat growth, using this procedure, have revealed two critical periods (vegetative and ear growth) when lack of moisture has the greatest impact on grain yields. Knowledge of these times could be useful in devising early warning programmes for drought amelioration, combined with reliable long-term climate forecasts. Decisions made during these critical periods would affect farm management, marketing strategy and planning for the next growing season. ©     

Modelling seasonal grain sorghum yields in subtropical Australia

The seasonal variability of irrigated grain sorghum yields has been examined in terms of the quantitative effects of environmental variables on the yield components of the average genotype using stepwise regression techniques. Flow models have been formulated of yield development indicating the likely pattern of interaction between plant and environmental factors.Growth before anthesis affected both leaf area development (amount and display) and the number of sites (flowers) where grain could be produced. The most important yield component was grain number per unit ground area and this, more than grain size, affected the amount of photosynthate which could be stored. An equation was developed in which the assimilate produced before anthesis could be partitioned between vegetative dry matter production and number of flowers, according to accumulated temperature and radiation.Anthesis assimilate supply played a rôle in determining actual grain number set and influenced initial grain growth rates—and hence potential grain size.Post-anthesis assimilate surplus determined actual grain development and was related to temperature and radiation terms. It has been postulated that the balance between assimilate supply and respiratory loads during grainfilling dictates not only the magnitude of the optimum temperature response surface but also the tuning of the optimal temperature. Under reduced assimilate surplus, grain sorghum showed temperate, rather than tropical, growth behaviour, posing potential limits for tropical production zones.