Simulation of the effect of forage cuttingg on subsequent grain yields of temperate cereals

Irrigated winter cereals (oats, barley, wheat, rye and triticale) were uncut or cut for forage at 80 days, 80 and 122 days, o4 80, 122 and 164 days from sowing. Grain yields following cutting were regressed on time before (or after) head emergence when the last cut occurred. The equations, of the form Y = A(1 ? Bexp (?CD)), were used to simulate different cutting regimes. They were also used to predict grain yields in other environments after estimating the date of head emergence and maximum yield of an uncut crop in that environment.All cereal cultivars were able to sustain at least one forage cut in mid-June before subsequent grain yields were reduced. With later cutting the rate of decrease in the grain yield was: wheat and rye > triticale and barley > oats. The ability to produce new basal tillers after extensive tiller decapitation appeared to be in the reverse order. In addition to a reduced number of heads (in wheat), grain yields decreased because of fewer grains per head (barley, wheat and triticale) and lower 1000-grain weights (wheat, rye and triticale).     

Effect of saline irrigation on germination and growth parameters of barley (Hordeum vulgare L.) in a pot experiment

The effect of saline irrigation was investigated on germination and growth parameters of six barley (Hordeum vulgare L.) cultivars in a pot experiment. The crop germination decreased between 24–35% with irrigation water having EC of 9.26 dS m⁻¹, 28–47% with water EC of 13.4 dS m⁻¹ and 30–53% with water EC of 16.28 dS m⁻¹ among various cultivars. The sequence of reduction in germination was Hassawi > Gusto > Madini > M. Khariji > Qassimi. Plant height and total number of plant tillers decreased significantly with increasing irrigation-water salinity. Plant height ranged between 39.43 cm (Qassimi cultivar) with water EC of 3.00 dS m⁻¹ to 1.97 cm (Gusto) with water EC of 16.28 dS m⁻¹ whereas the range for total number of plant tillers per pot was 77.00 (Qassimi) with irrigation EC of 3.00 dS m⁻¹ to 9.67 (Gusto) with irrigation EC of 16.28 dS m⁻¹. The trend of reduction in plant height for different cultivars was Gusto > Qassimi > Hassawi > Madini > M. Khariji whereas for plant tillers, the sequence was Gusto < Hassawi < M. Khariji < Qassimi < Madini. Greenmatter and drymatter yield decreased significantly with increasing irrigation water salinity. The greenmatter yield ranged between 138.67 g per pot (Madini) with water EC of 3.00 dS m⁻¹ to 11.40 g per pot (Gusto) with water EC of 16.28 dS m⁻¹. A similar trend was found for drymatter yield. The trend of reduction in yield among various cultivars (both greenmatter and drymatter) was Gusto > Hassawi > M. Khariji > Qassimi > Madini. Overall sequence of salt tolerance for different barley cultivars was Madini > Qassimi > M. Khariji > Hassawi > Gusto. A comparison of cultivars indicated that irrigation waters with EC 13.40 dS m⁻¹ and above reduced crop germination and greenmatter production to a significant level. In conclusion, there exists a lot of potential for a reasonable production of barley as forage crop with irrigation water having salinity up to 9.26 dS m⁻¹ provided 15% extra water above crop-water requirement is applied as leaching requirements to control soil salinity.     

Effect of irrigation application depth on cereal production in the semi-arid climate of southern Alberta

Different water application depths and irrigation intervals were compared for two cereal crops in southern Alberta. Four irrigation treatments and three fertilizer N treatments were applied to soft white wheat in 1987 and 1988 and barley in 1989 and 1990 on a Lethbridge loam. The treatments were light, frequent irrigation for the whole growing season (F), conventional irrigation for the whole growing season (C), light, frequent irrigation until heading, followed by conventional irrigation (FC), and conventional irrigation until heading, followed by light, frequent irrigation (CF). Fertilizer N as ammonium nitrate was broadcast in the spring at 0, 60 and 120 kg N ha^-1. Light frequent irrigations for the entire growing season increased wheat straw yield compared to the conventional irrigation treatment (5211kg ha^-1 vs 4152 kg ha^-1, respectively). Straw yield with F irrigation for part of the growing season was intermediate between the other two irrigation treatments. Irrigation treatment did not affect soft white wheat grain yield. Barley straw yield was not affected by irrigation treatment but barley grain yield was greater for the C irrigation treatment than the F and FC treatments (4924 kg ha^-1 vs 4177 kg ha^-1, respectively). Lodging was evident in the barley crops, particularly with F irrigation in the first half of the growing season. Grain/straw ratios were greater for the C than the other irrigation treatments. Higher water use in the F than the C treatment in the higher water stress years (1988 and 1989) was balanced with greater vegetative growth. In the lower water stress growing seasons (1987 and 1990), higher water use in the C than the F treatment was attributed to deep percolation. Water use efficiency (WUE) was generally not affected by irrigation treatment except for barley in 1989, when lower WUE values in the F than the C treatment were associated with severe lodging.     

Effect of small irrigation amounts on the yield of wheat

Yields of dryland crops are governed by the moisture in the soil profile at seeding and by rainfall during the growing season. Occasionally limited amounts of water may also be available for irrigation. Field experiments were conducted over a period of 4 years on loamy sand and 3 years on sandy loam to study the effects of pre-seeding, post-seeding and split application of limited amounts of water on root growth, water use, dry matter accumulation and grain yield of wheat. This article reports the treatment effects on dry matter accumulation and grain yield.Early season water stress decreased the rate of dry matter accumulation. Grain yield responded significantly to irrigation 30 days after seeding irrespective of the amount of water, year and soil type. Yield with post-seeding irrigation averaged 3518 kg ha^?1 against 2317 kg ha^?1 for unirrigated control in loamy sand and 4440 kg ha^?1 against 3391 kg ha^?1 in sandy loam. The increase in yield was manifested by a significant increase in the number of effective tillers per m row length, number of grains per ear and thousand grain weight.     

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.     

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     

Effect of saline water irrigation and manure application on the available water content, soil salinity, and growth of wheat

Good water management combined with appropriate soil management is necessary for sustainable crop production in drylands. A pot culture experiment was conducted using sand dune soil under greenhouse conditions to evaluate the response of wheat (Triticum aestivum L.) to the application of farmyard manure (FYM) or poultry manure (PM), and irrigation with water at two salinity levels (0.11 and 2.0 dS m⁻¹) and two irrigation intervals (daily and every second day). The manure was applied at a rate of 20 Mg ha⁻¹. The soil water content, measured 1 h before every irrigation, showed that soil treated with PM retained more water than that treated with FYM, while the control (no manure) contained the least water. FYM treatment resulted in 78 and 21% higher dry matter yield compared to the control and PM treatments, respectively, under daily irrigation using good-quality water. The increase was 29 and 55%, respectively, when saline water was used for daily irrigation. A similar trend was observed with the alternate day irrigation treatment; FYM gave the highest dry matter yield. The number of tillers and plant height showed that FYM was better than PM, which in turn was better than the control under irrigation with good-quality water regardless of the irrigation interval. When water of the highest salinity was used for irrigation, FYM was still always the best, but the control was now better than the PM treatment. The electrical conductivity of the soil measured at the end of the experiment was slightly higher with PM, as compared to the FYM and control treatments. A significant interaction between irrigation water quality and manure application was observed, affecting plant growth. PM aggravated the adverse affect of saline water on plant growth by increasing soil salinity.     

Water use and water-use efficiency of wheat and barley in relation to seeding dates,levels of irrigation and nitrogen fertilization

Response of timely and late seeded wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) to three levels of irrigation and four rates of nitrogen was investigated under pre-seeding irrigation. Water extraction pattern and water use of these crops varied markedly. Barley outyielded wheat by 27 and 9%, but used 9 and 21 mm less water, when one and two irrigations were given at critical stages, respectively. These results indicate the possibilities of considerable saving of water (100 mm) for barley without any decrease in grain yield and increased water-use efficiency (WUE) of wheat and barley by irrigating at critical stages as compared to irrigation at 75% depletion of available soil water (ASW). In general WUE decreased with increase in irrigation frequency and delay in seeding.Nitrogen fertilization with marginal additional water use (4–9%) increased yield linearly (45–98%) and thus increased WUE of wheat and barley. This additional water was extracted from below 60 cm depth at tensions ? 1.5 MPa and particularly in maximum growth and reproductive stages. These results suggest that barley should be preferred to wheat under medium to severe water stress and late seeding conditions.     

Water-yield relations and water-use efficiency of winter wheat in the North China Plain

Limited precipitation restricts yield of winter wheat (Triticum aestivum L.) grown in the North China Plain. Water stress effects on yield can be avoided or minimized by application of irrigation. We examined the multiseasonal irrigation experiments in four locations of the piedmont and lowland in the region, and developed crop water-stress sensitivity index, relationship between seasonal evapotranspiration (ET) and yield, and crop water production functions. By relating relative yield to relative ET deficit, we found that the crop was more sensitive to water stress from stem elongation to heading and from heading to milking. For limited irrigation, irrigation is recommended during the stages sensitive to water stress. Grain yield was 258–322 g m⁻² in the piedmont and 260–280 g m⁻² in the lowland under rainfed conditions. The corresponding seasonal ET was 242–264 mm in the piedmont and 247–281 mm in the lowland. Irrigation significantly increased seasonal ET and therefore grain yield as a result of increased kernel numbers per m⁻² and kernels per ear. On average, one irrigation increased grain yield by 21–43% and two to four irrigations by 60–100%. Grain yield was linearly related to seasonal ET with a slope of 1.15 kg m⁻³ in the lowland and 1.73 kg m⁻³ in the piedmont. Water-use efficiency was 0.98–1.22 kg m⁻³ for rainfed wheat and 1.20–1.40 kg m⁻³ for the wheat irrigated 2–4 times. Grain yield response to the amount of irrigation (IRR) was developed using a quadratic function and used to analyze different irrigation scenarios. To achieve the maximum grain yield, IRR was 240 mm in the piedmont and 290 mm in the lowland. When the maximum net profit was achieved, IRR was 195 mm and 250 mm in the piedmont and lowland, respectively. The yield response curve to IRR showed a plateau over a large range of IRR, indicating a great potential in saving IRR while maintaining reasonable high levels of grain yield.     

Response of two-row malting spring barley to water cutoff under sprinkler irrigation

Agricultural production in irrigated areas is becoming more water-constrained. Scheduling the timing of the last irrigation on cereals is one effective method of reducing seasonal water use while maintaining crop yield and quality. The last irrigation application time and its impact on two-row malting barley (Hordeum distichum cv. Moravian 37) yield, quality, and economic benefits were studied in the 2000, 2001, and 2002 cropping seasons. Irrigation was stopped for the season at Milk, pre-Soft Dough, Soft Dough, and post-Soft Dough grain formation stages. The Soft Dough water cutoff treatment produced the highest grain yield of two-row spring malting barley. Water cutoff before or after Soft Dough stage reduced the grain yield significantly at P < 0.05, but the quality of grain for malt production was not significantly different when water was cut off at pre-Soft Dough or post-Soft Dough stages. Irrigation cutoff at Milk stage produced the lowest grain yield with the lowest quality. Decreases in grain yield and quality with the last irrigation at post-Soft Dough reduced grain value by $174 ha⁻¹ relative to Soft Dough, while irrigation costs were higher (Fig. 6). The economic benefit due to labor and power cost reduction from earlier irrigation cutoff does not offset the resulting loss of grain value/ha for any treatment except post-SD under current southern Idaho energy and labor cost conditions.     

Can carbon isotope discrimination and ash content predict grain yield and water use efficiency in wheat?

Drought is the main factor affecting crop grain yield. Increasing grain yield under drought and crop water use efficiency (WUE) is essential for enhancing world crop production and food availability. The objective of this study, carried out in India on 20 durum wheat cultivars, under three water regimes (full irrigation, limited irrigation and residual soil moisture) and during two seasons, was to investigate the potential use of plant traits (particularly carbon isotope discrimination, Δ, and ash content, m_a) to predict grain yield and WUE in wheat. WUE components were estimated using a soil water balance model (Budget) allowing comparison of environments in data scarce situations. A highly significant correlation was noted between grain yield and grain Δ across water regimes. However, the associations between grain yield, Δ and m_a were found to depend highly on the water regime and environmental conditions. The association between grain yield and grain Δ was significant under full irrigation in season 1 and under residual soil moisture in season 2. Significant positive correlations were noted in both seasons between grain yield and leaf Δ under residual soil moisture and between grain yield and leaf ash content at anthesis under limited irrigation. A significant correlation was found across environments between grain and leaf Δ and T, the quantity of water transpired during the growth cycle, as estimated by the soil water balance model. T also significantly correlated to grain and leaf m_a. Variation in WUE across environments was driven more by runoff, drainage and soil evaporation than by harvest index and transpiration. The associations between WUE and transpiration, runoff and Δ were negative but not significant. WUE was significantly correlated with leaf and grain m_a at maturity. The study indicates that Δ and m_a can be used as indirect selection criteria for grain yield and suggests that m_a is a good predictor of transpiration, grain yield and WUE across environments. The use of mechanistic models that allows differentiating between cultivars should permit in a next future to analyze the relationships between WUE, Δ and m_a across cultivars and evaluate the possibility to use these traits as predictors of WUE in wheat breeding programs.     

Cotton yield and applied water relationships under drip irrigation

Different irrigation scheduling methods and amounts of water ranging from deficit to excessive amounts were used in cotton (Gossypium hirsutum L.) irrigation studies from 1988 to 1999, at Lubbock, TX. Irrigation scheduling treatments based on canopy temperature (T_c) were emphasized in each year. Surface drip irrigation and recommended production practices for the area were used. The objective was to use the 12-year database to estimate the effect of irrigation and growing season temperature on cotton yield. Yields in the irrigation studies were then compared with those for the northwest Texas production region. An irrigation input of 58 cm or total water application of 74 cm was estimated to produce maximum lint yield. Sources of the total water supply for the maximum yielding treatments for each year averaged 74% from irrigation and 26% from rain. Lint yield response to irrigation up to the point of maximum yield was approximated as 11.4 kg ha⁻¹ cm⁻¹ of irrigation between the limits of 5 and 54 cm with lint yields ranging from 855 to 1630 kg ha⁻¹. The intra-year maximum lint yield treatments were not limited by water input, and their inter-year range of 300 kg ha⁻¹ was not correlated with the quantity of irrigation. The maximum lint yields were linearly related to monthly and seasonal heat units (HU) with significant regressions for July (P=0.15), August (P=0.07), and from May to September (P=0.01). The fluctuation of maximum yearly lint yields and the response to HU in the irrigation studies were similar to the average yields in the surrounding production region. The rate of lint yield increase with HU was slightly higher in the irrigation studies than in the surrounding production area and was attributed to minimal water stress. Managing irrigation based on real-time measurements of T_c produced maximum cotton yields without applying excessive irrigation.     

Water–yield relations and optimal irrigation scheduling of wheat in the Mediterranean region

Crop yield is primarily water-limited in areas of West Asia and North Africa with a Mediterranean climate. Ten years of supplemental irrigation (SI) experiments in northern Syria were conducted to evaluate water–yield relations for bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L.), and optimal irrigation scheduling was proposed for various rainfall conditions. The sensitive growth stages of wheat to water stress were from stem elongation to booting, followed by anthesis, and grain-filling. Water stress to which crop subjected depends on rainfall and its distribution during the growing season; the stress started from early March (stem-elongation stage) or even in seedling stage in a dry year, and from mid-April (anthesis) in an average or wet year. Crop yield linearly increased with increase in evapotranspiration (ET), with an increase of 160 kg for bread wheat and of 116 kg for durum wheat per 10 mm increase of ET above the threshold of 200 mm. Water-use efficiency (WUE) with a yield ≥3 t ha⁻¹ was ca. 60% higher than that with yield <3 t ha⁻¹; this emphasises the importance of that to achieve effective use of water, optimal water supply and relatively high yields need to be ensured. Quadratic crop production functions with the total applied water were developed and used to estimate the levels of irrigation water for maximizing yield, net profit and levels to which the crops could be under-irrigated without reducing income below that which would be earned for full SI under limited water resources. The analysis suggested that irrigation scenarios for maximizing crop yield and/or the net profit under limited land resource conditions should not be recommended. The SI scenarios for maximizing the profit under limited water resource conditions or for a targeted yield of 4–5 t ha⁻¹ were recommended for sustainable utilization of water resources and higher WUE. The time of irrigation was also suggested on the basis of crop sensitivity index to water stress taking rainfall probability and available soil water into account.     

Optimizing irrigation scheduling for winter wheat in the North China Plain

In the North China Plain (NCP), more than 70% of irrigation water resources are used for winter wheat (Triticum aestivum L.). A crucial target of groundwater conservation and sustainable crop production is to develop water-saving agriculture, particularly for winter wheat. The purpose of this study was to optimize irrigation scheduling for high wheat yield and water use efficiency (WUE). Field experiments were conducted for three growing seasons at the Wuqiao Experiment Station of China Agriculture University. Eleven, four and six irrigation treatments, consisting of frequency of irrigation (zero to four times) and timing (at raising, jointing, booting, flowering and milking stage), were employed for 1994/95, 1995/96 and 1996/97 seasons, respectively. Available water content (AWC), rain events, soil water use (SWU), evapotranspiration (ET) and grain yield were recorded, and water use efficiency (WUE) and irrigation water use efficiency (IWUE) were calculated.The results showed that after a 75-mm pre-sowing irrigation, soil water content and AWC in the root zone of a 2-m soil profile during sowing were 31.1% (or 90.7% of field capacity) and 16.1%, respectively. Rainfall events were variable and showed a limited impact on AWC. The AWC decreased significantly with the growth of wheat. At the jointing stage no water deficits occurred for all treatments, at the flowering stage water deficits were found only in the rain-fed treatment, and at harvest all treatments had moderate to severe soil water deficits. The SWU in the 2-m soil profile was negatively related to the irrigation water volume, i.e. applying 75 mm irrigation reduced SWU by 28.2 mm. Regression analyses showed that relationships between ET and grain yield or WUE could be described by quadratic functions. Grain yield and WUE reached their maximum values of 7423 kg/ha and 1.645 kg/m³ at the ET rate of 509 and 382 mm, respectively. IWUE was negatively correlated with irrigated water volume. From the above results, three irrigation schedules: (1) pre-sowing irrigation only, (2) pre-sowing irrigation + irrigation at jointing or booting stage, and (3) pre-sowing irrigation + irrigations at jointing and flowering stages were identified and recommended for practical winter wheat production in the NCP.     

Use of a water deficit sensitivity index for partial irrigation scheduling of wheat and barley

Shortage of water is the most important limiting factor for crop production in the arid and semi-arid regions in Iran. More land can become productive by using partial irrigation at strategic times during the growing season. This may be accomplished if a proper index of crop sensitivity to water deficit at various growth stages is used. A theoretical procedure was applied to determine the savings in water and the economic benefit derived from partial irrigation, using a water stress sensitivity index for winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.) in a dry region of Fars province in Iran. The results indicated that some water reduction is possible. In general, the suggested maximum allowable water reduction was unreasonably high for the sensitivity index (λ _i ) proposed by Nairizi and Rydzewski. Their index is not applicable in arid and semi-arid areas. However, the field-derived λ _i of Aryan resulted in a reasonable water reduction close to the field-applied water reduction to achieve a corresponding relative yield. Therefore, appropriate values of λ _i for different climatic conditions should be used to calculate rational water reductions. The maximum allowable water reduction for spring barley was higher than that for winter wheat. The reduction increased as the benefit to cost ratio (B/C) was increased. Water reductions of 7 and 26% were allowed for winter wheat and spring barley, respectively, at a B/C ratio of 1.5. This corresponded to an 8 and 35% increase in cultivated area, respectively. These results need to be validated in more extensive field experimentation. Received: 9 December 1994     

Irrigation effects on the growth, yield, and water use efficiency of alfalfa

A field study was conducted in the semiarid region of northern Sudan to investigate the effects of variable irrigation on the growth, yield, and water use efficiency (WUE) of alfalfa (Medicago sativa L.). Treatments were 65 mm of water applied every 7 days, 80 mm of water applied every 10 days, or 104 mm of water applied every 13 days. The heavy, infrequent irrigation reduced stem height, stem density, leaf area index (LAI), total biomass production, and the WUE of alfalfa plants. Maximum yields for six harvests were 15.3, 12.9, and 11.2 ton ha^–1 and the WUE values were 0.12, 0.10, and 0.08 ton ha^–1 cm^–1 for the frequent, less-frequent, and infrequent irrigation regimes, respectively. In all the treatments, alfalfa dry matter yield was positively correlated with stem height and LAI. The relationship between dry matter yield and total water use was a linear function (R ²=0.99), regardless of the irrigation treatment. Alfalfa growth, yield, and WUE remained high during the relatively cool months and declined during the hot period under the three water regimes. It was concluded that alfalfa grown under semiarid conditions should be watered lightly and frequently to attain high yields and high WUE. Received: 19 February 1996     

冬小麦冬灌、秸秆覆盖、后期喷生长剂的节水增产效果的研究

试验证明，适时冬灌比早春灌，具有良好的防旱防冻、促根壮蘖增穗作用；小麦越冬期秸秆覆盖能保墒和提高土壤水分的调节能力，为当季小麦生长和套播玉米创造适宜的土壤水分条件；于小麦孕穗和灌浆期喷翠竹生长剂，其增粒增重作用显著。采取冬灌、越冬秸秆覆盖和孕穗、灌浆期喷生长剂等配套措施，可实现保墒与节水相结合，壮苗促蘖增穗与增粒增重的统一，节水增产效果显著。     

Irrigation strategies to improve the water use efficiency of wheat-maize double cropping systems in North China Plain

Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm³ cm⁻³, 0.59 Mg ha⁻¹, 2.05 Mg ha⁻¹, and 0.19 kg m⁻³, respectively, for wheat; and 0.027 cm³ cm⁻³, 0.71 Mg ha⁻¹, 1.51 Mg ha⁻¹ and 0.35 kg m⁻³, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.     

灌排模式和施氮水平对水稻株高与茎蘖生长动态的影响

为探究灌排模式、施氮水平对水稻株高、茎蘖生长动态的影响,以稻田水位作为调控指标,通过测坑控水试验,采用Logistic曲线以及DMOR数学模型定量分析不同施氮水平下分蘖期先旱后涝（FHL）、拔节孕穗期先旱后涝（BHL）以及控制灌排（CID）3种处理对株高、茎蘖生长动态的影响。结果表明：灌排模式主要通过改变水稻株高、茎蘖的生长时间以及生长速率来影响株高、茎蘖生长,最大株高由大到小表现为CID处理、FHL处理、BHL处理,最大茎蘖数由大到小表现为CID处理、BHL处理、FHL处理。施氮主要是通过提高水稻株高、茎蘖的生长速率来促进株高、茎蘖生长;最大株高随着施氮量的增加而增加,CID和FHL两种处理下,最大株高由施氮150kg/hm2的98.9、97.8cm增加到施氮300kg/hm2的102.4、101.2cm,继续施氮没有显著提高;CID处理和BHL处理下,最大茎蘖数随着施氮量的增加而增加;FHL处理下,低氮处理和高氮处理的最大茎蘖数显著小于中氮处理。灌排模式与施氮水平的交互作用对株高、茎蘖数动态过程均有极显著影响,增施氮肥在一定程度上可以缓解因水分胁迫所引起的株高、茎蘖数的下降,但是高氮会加重水分胁迫,不利于株高、茎蘖的生长。     

In-season wheat root growth and soil water extraction in the Mediterranean environment of northern Syria

Wheat is the most important cereal crop in the semi-arid eastern Mediterranean region that includes northern Syria. Knowledge of wheat root depth and the vertical distribution during the winter growing season is needed for sound scheduling of irrigation and efficient use of water. This article reports evaluation of root development for three winter-grown bread (Triticum aestivum L.) and durum (Triticum turgidum L.) wheat under four soil water regimes (rainfed and full irrigation with two intermediate levels of 33 and 66% of full irrigation). Roots were sampled by soil coring to a depth of 0.75 m at four occasions during 2005-2006 growing season. Two distinct phases of root development were identified, a rapid downward penetration from emergence to end tillering phase, followed by a substantial root mass growth along the profile from tillering to mid-stem-elongation phase. Roots were detected as deep as 0.75 m during the initial rapid penetration, yet only 29% of the total seasonal root mass was developed. This downward penetration rate averaged 7 mm d⁻¹ and produced 10.8 kg ha⁻¹ d⁻¹ of root dry-biomass. The bulging of root mass from tillering to mid-stem-elongation coincided with vigorous shoot growth, doubling root dry-biomass at a rate of 52 kg ha⁻¹ d⁻¹, compared to the seasonal root growth rate of 18.3 kg ha⁻¹ d⁻¹. A second-degree equation described the total root dry-biomass as a function of days after emergence (r² = 0.85), whereas a simpler equation predicted it as a function of cumulative growing degree days (r² = 0.85). The final grain yield was a strong function of irrigation regimes, varying from 3.0 to 6.5 t ha⁻¹, but showed no correlation with root biomass which remained similar as soil water regimes changed. This observation must be viewed with care as it lacks statistical evidence. Results showed 90% of root mass at first irrigation (15 April) confined in the top 0.60-0.75 m soil in bread wheat. Presence of shallow restricting soil layers limited root depth of durum wheat to 0.45 m, yet total seasonal root mass and grain yield were comparable with non-restricted bread wheat. Most root growth occurred during the cool rainy season and prior to the late irrigation season. The root sampling is short of rigorous, but results complement the limited field data in literature collectively suggesting that irrigation following the rainy season may best be scheduled assuming a well developed root zone as deep as the effective soil depth within the top meter of soil.