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1.
Summary A field trial was conducted to determine the response of rapeseed (Brassica napus cv. Marnoo) to two irrigation treatments and six nitrogen fertilizer treatments. Response to nitrogen was greater with than without irrigation. Oil content was increased with irrigation but decreased under increasing nitrogen application, and was inversely related to seed nitrogen concentration. Oil yields averaged 1,168 kg ha–1 under irrigated treatments compared with 835 kg ha–1 under rainfed treatments. Maximum oil yield (approx. 1,557 kg ha–1) was obtained from the irrigated treatment fertilized with 100 kg N ha–1 applied at sowing.  相似文献   

2.
Summary Empirical functions to predict the nitrogen uptake, increase in LAI and minimum leaf water potential (LWP) of cotton were incorporated into a water balance model for the Namoi Valley, N.S.W. A function was then developed to describe the lint yield of irrigated cotton as a function of water stress days at 4 stages of development, total nitrogen uptake and days of waterlogging. A water stress day was defined as predicted minimum leaf water potential less than -1.8 MPa up to 90 days after sowing and -2.4 MPa there-after; stress reduced yield by up to 40 kg lint ha–1 d–1 with greatest sensitivity at 81–140 days after sowing and when N uptake was highest. Nitrogen uptake was reduced by 0.98 kg per ha and yield reduced by 33.2 kg lint ha–1 for each day of waterlogging. The model was used to evaluate various irrigation strategies by simulating production of cotton from historical rainfall data. With a water supply from off farm storage, net returns ($ M1–1) were maximized by allocating 7 Ml ha–1 of crop. The optimum practice was not to irrigate until 60 days from sowing and until the deficit in the root zone reached 50%. When the supply of water was less than 7 Ml ha–1 there was no advantage in either delaying the start of irrigation or irrigating at a greater deficit; it was economically more rational to reduce the area shown or, if already sown, to irrigate part with 6 Ml ha–1 and leave the rest as a raingrown crop. Irrigation decisions are compromises between reducing the risk of water stress and increasing the risk of waterlogging. The simulation showed that there is no single set of practices that is always best in every season; in a number of seasons practices other than those which on average are best, give better results.  相似文献   

3.
Summary To determine if drip irrigation increases fertilizer requirements and/or the efficiency of utilization compared to furrow irrigation, growth and nitrogen uptake were measured in a four-year experiment comparing surface (SD) and buried (BD) methods of drip irrigation with furrow irrigation (F) of cotton. The soil was a slowly-permeable cracking grey clay (vertisol) at Narrabri, N.S.W Drip-irrigated treatments were maintained at a deficit of 45 mm below the fully-irrigated soil water content, while F was irrigated when the deficit reached about 90 mm. Nitrogen (N) fertilizer was applied weekly with drip irrigation to BD and SD over the first half of the season, and as a conventional single application to F before sowing. Leaf area index (LAI), dry matter and N uptake were influenced more by season than by method of irrigation. LAI during boll filling averaged 2.4 and was 10% greater in BD than in SD and F. Final dry matter averaged 988 g m–2 and was 10% greater in BD and SD than in F. The efficiency of conversion of solar radiation into dry matter averaged 0.55 g MJ–1; lint yield as a fraction of dry matter averaged 0.18; neither parameter was consistently influenced by the method of irrigation. Total N uptake ranged from 97 to 170 kg ha–1 and was influenced by irrigation method in one season only, when it was less in F than in SD and BD. N was often taken up later under drip irrigation than under F: there was up to 40% less N taken up by SD than F in the early flowering stage. The delay was associated with later application of N to BD and SD compared with F, and the application of N to the surface of alternate furrows of SD. Plant factors such as root ageing and competition between roots and bolls, were also implicated. We conclude that all of the N should be applied to drip-irrigated cotton on these soils by mid flowering, and that some of the N should be applied in the soil before sowing.  相似文献   

4.
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.  相似文献   

5.
Summary Cotton was grown under sprinkler irrigation on a silty clay soil at Keiser, Arkansas, for the 1987, 1988 and 1989 growing seasons. Irrigation treatments consisted of maximum soil water deficits (SWD) of 25, 50 and 75 mm and a nonirrigated control. While the irrigated treatments were significantly different from the control for plant height and total seedcotton yield, significant differences among the three irrigated treatments were only observed for plant height. Yields were significantly lower in 1989 than in the other two years of the study, due in part to later planting. The 3-year averages for total seedcotton yield were 3280 and 2870 kg ha–1 for irrigated and nonirrigated, respectively, for an average increase corresponding to irrigation of 416 kg ha–1 or 14.5% of the nonirrigated yield. The maximum increase was observed in 1988 as 602 kg ha–1 or 20.6% of the nonirrigated yield for that year. The 75 mm allowable SWD was the most efficient treatment and resulted in a 3-year average of 3.85 kg ha–1 additional seedcotton (above the nonirrigated) harvested for each 1 mm of irrigation applied. Maintaining the SWD below a 75 mm maximum required an average of four irrigations and 110 mm of irrigation water per year.  相似文献   

6.
Nitrogen (N2) fixation in an irrigated white clover-grass sward was estimated using the 15N isotope dilution technique following the addition of K15NO3 at 0.5 gN m–2 and 80 atom % 15N in a field study during the 1990–91 season. Two water salinity treatments (channel water; ECw = 0.07 and groundwater; 2.4 dS m–1) and four irrigation frequencies were included in a factorial design with four replicates. The channel water treatments were irrigated when pan evaporation minus rainfall equalled 50 mm, whereas the groundwater treatments were irrigated at deficits of 40, 50, 65 or 80 mm. Cumulative dry matter of the clover was significantly less in treatments irrigated with saline groundwater compared to channel water at day 164, and soil salinities (ECe) increased on average from 2.3 to 5.07 dS m–1. In contrast, salinity of the irrigation water had no effect on the cumulative yield of grass. Cumulative dry matter of the grass and clover were not affected by groundwater irrigation frequency. Total N accumulation by the grass did not differ significantly between treatments. However, total N accumulation in white clover was significantly less (P < 0.05) in all treatments irrigated with groundwater compared to channel water. Neither the N concentrations of the grass nor the clover differed significantly between the salinity treatments. Salinity and irrigation frequency had no effect on the proportion of clover N (Patm) derived from N2 fixation. The values of Patm were high throughout, and increased progressively from 0.78 at day 39 to 0.91 at day 164 (P < 0.01). However, the yield of fixed N was lower in clover when watered with groundwater compared to channel water (P < 0.01). Thus low to moderate soil salinity did not affect the symbiotic dependence of clover, but the yield of biologically-fixed N was depressed through a reduction in the dry matter yield of the legume.  相似文献   

7.
Summary Four irrigation treatments: no irrigation; early irrigation (150 mm); late irrigation (150 mm); and early+late irrigation (275 mm), with 363 mm of rain; and four basic applications of nitrogen (0, 60, 120, 180 kg ha–1), with and without an additional nitrogen top dressing of 60 kg ha–1, were applied to autumn-sown wheat.For any given total nitrogen rate, there was no difference between the single and the split application.Grain yields ranged from 3040 kg ha–1 for the unirrigated, zero-nitrogen treatment to 6340 kg ha–1 for the two irrigations, 180 kg ha –1 N treatment. There was a strong interaction of irrigation and nitrogen on grain yields which was due mainly to the late irrigation: in the absence of the late irrigation the optimal nitrogen rate was 120 kg hat, followed by a marked decline in yield with additional nitrogen, whereas the application of the late irrigation shifted the optimum nitrogen rate to 180 kg ha–1. In the absence of the late irrigation, increasing the nitrogen rate from 0 to 240 kg ha –1 reduced kernel weight from 42 to 32 mg, whereas late irrigation largely prevented this decrease (42 to 39 mg). The reduction in kernel weight was evident even at the first nitrogen increments, in the range where grain yield was still increasing. Lack of nitrogen reduced soil moisture extraction during the grain filling stage, particularly from soil layers deeper than 60 cm.Stomatal aperture in the irrigated treatments was markedly larger in nitrogen-supplied than in nitrogen-deficient wheat, although the leaf hydration was similar; in the unirrigated treatment, the nitrogen-supplied plants had a lower hydration and smaller stomatal aperture than nitrogen-deficient plants.Contribution from the Agricultural Research Organization, Bet Dagan, Israel, No: 282-E, 1977 series  相似文献   

8.
The effects of high temperature stress and supplemental irrigation on seed yield and water use efficiency (WUE) of canola (Brassica napus L.) were studied in a field experiment conducted for 2 years. The experiment was a randomized complete block design arranged in split plot, conducted at Agricultural Research Station of Gonbad, Iran. It was arranged in two conditions, i.e. supplemental irrigation and rainfed. Two cultivars of canola (Hyola401 and RGS003) as subplots were grown at five sowing dates as main plots. The sowing dates were 9 November, 6 December, 5 January, 4 February and 6 March in 2005-2006 and 6 November, 6 December, 5 January, 4 February and 6 March in 2006-2007, to have a wide range of environmental conditions around flowering and seed filling periods, and to coincide reproductive stages of the crop with high temperature stress. Seed yield was improved due to field management practices, such as supplemental irrigation and optimum sowing date. Supplemental irrigation was an efficient practice to mitigate water stress, and to increase aboveground dry matter and seed yield. There was a strongly negative relationship between seed yield and air temperature during reproductive stages. Delay in sowing led to more rapid developmental of canola, decreased aboveground dry matter, leaf area index (LAI), harvest index (HI), WUE, and seed yield. Achieving a high aboveground dry matter was an essential prerequisite for high reproductive growth and a high seed yield. Greater seed yield and WUE at first sowing date were associated with greater LAI and aboveground dry matter, and lower temperatures during reproductive stages. The results support the view that WUE can be used as an indirect selection criterion for seed yield in genotypic selection.  相似文献   

9.
Field experiments were conducted for 2 years to investigate the effects of various levels of nitrogen (N) and methods of cotton planting on yield, agronomic efficiency of N (AEN) and water use efficiency (WUE) in cotton irrigated through surface drip irrigation at Bathinda situated in semi-arid region of northwest India. Three levels of N (100, 75 and 50% of recommended N, 75 kg ha−1) were tested under drip irrigation in comparison to 75 kg of N ha−1 in check-basin. The three methods of planting tried were; normal sowing of cotton with row to row spacing of 67.5 cm (NS), normal paired row sowing with row to row spacing of 35 and 100 cm alternately (NP) and dense paired row sowing with row to row spacing of 35 and 55 cm alternately resulting in total number rows and plants to be 1.5 times (DP) than NS and NP. In NS there was one lateral along each row, but in paired sowings there was one lateral between each pair of rows. Consequently the number of laterals and quantity of water applied was 50 and 75% in NP and DP, respectively, as compared with NS in which irrigation water applied was equivalent to check-basin.Drip irrigation under NS resulted in an increase of 258 and 453 kg ha−1 seed cotton yield than check-basin during first and second year, respectively, when same quantity of water and N was applied. Drip irrigation under dense paired sowing (DP) in which the quantity of irrigation water applied was 75% as compared with NS, further increased the yield by 84 and 101 kg ha−1 than NS during first and second year, respectively. Drip irrigation under NP, in which the quantity of water applied and number of laterals used were 50% as compared with drip under NS, resulted in a reduction in seed cotton yield of 257 and 112 kg ha−1 than NS during first and second year, respectively. However, the yield obtained in NP under drip irrigation was equivalent to yield obtained in NS under check-basin during first year but 341 kg ha−1 higher yield was obtained during second year. The decrease in N applied, irrespective of methods of planting, caused a significant decline in seed cotton yield during both the years. Water use efficiency (WUE) under drip irrigation increased from 1.648 to 1.847 and from 0.983 to 1.615 kg ha−1 mm−1 during first and second year, respectively, when the same quantity of N and water was applied. The WUE further increased to 2.125 and 1.788 kg ha−1 mm−1 under DP during first and second year, respectively. The agronomic efficiency of nitrogen was higher in drip than check-basin during both the years when equal N was applied. The WUE decreased with decrease in the rate of N applied under fertigation but reverse was true for AEN. It is evident that DP under drip irrigation resulted in higher seed cotton yield, WUE and AEN than NS and also saved 25% irrigation water as well as cost of laterals.  相似文献   

10.
The fate of nitrogen applied to sugarcane by trickle irrigation   总被引：1，自引：0，他引：1  
Fertigation can be a more efficient means of applying crop nutrients, particularly nitrogen (N), so that nutrient application rates can be reduced in fertigated crops. However, there is little information on the extent of the possible reduction in N application rate for fertigated sugarcane, one of the major row crops grown under trickle irrigation, nor the fate of N in fertigated sugarcane systems if N application rates are not reduced. An experiment was established to determine the response of cane and sugar production to different N rates (0–240 kg ha–1 year–1) spanning that recommended for conventional irrigation systems (160 kg ha–1 year–1). As well as yield, N removed in the crop and changes in soil mineral N were determined annually for four crops (a plant and three ratoon crops). 15N values were also measured in selected treatments at selected times to assess possible N inputs to the experiment via biological N fixation (BFN). Yields of cane and sugar responded to application of N fertiliser in the three ratoon crops, but they were not significantly increased by applying more than 80 kg ha–1 of N. There were no N responses in the plant crop, as there was >200 kg ha–1 of soil mineral N (SMN) to 2 m depth at the site prior to planting, and much of this SMN was depleted in the treatment receiving no N. There was no evidence of N input from BFN in the experiment. During the 4-year study period, net removal of N from the treatment with no applied N totalled 207 kg ha–1. When 80 or 120 kg ha–1 year–1 of N was applied to ratoon crops, outputs of N from the harvested crop approximately balanced inputs from fertiliser and depletion of SMN during the experiment. Inputs clearly exceeded output at higher N application rates. Assuming that the net removal of N from the treatment with no applied N was the same as the net mineralisation of N from soil organic matter in all treatments in the experiment, 204–639 kg ha–1 of N was unaccounted for in the treatments with applied N over the duration of the experiment. While some of this N (e.g. 45 kg ha–1) may have resulted in small (and undetectable) increases in total soil N, much of it would have been lost to the environment. We suggest that the high soil water contents maintained with daily application of irrigation water through the trickle system promotes mineralisation of soil organic matter and hence losses of N to the environment. Thus, particular care is required to avoid over-application of N in fertigated sugarcane.Communicated by K. Bristow  相似文献   

11.
Irrigation for crops in a sub-humid environment   总被引：4，自引：0，他引：4  
Summary A four year study examined the effect of irrigating at various water deficits at different times in the growing season, in combination with a range of nitrogen fertilizer rates, on the growth, yield and quality of cotton. The major effect of irrigation treatment on growth was to increase leaf area and plant size; net assimilation rate in the vegetative phase was not affected by irrigation treatment. The initial rate of boll setting was slightly faster in low nitrogen and less frequent irrigation treatments, but by day 180 (immediately prior to defoliation), all treatments had 60% of total dry weight as bolls and 7% as leaf. The best irrigation strategy varied from year to year due to the variable rainfall pattern. Irrigation when 80% of the available soil moisture had been depleted in the first half of the season only decreased total lint yield by up to 12% in two of the four seasons. During the second half of the season the 80% level of depletion decreased yield by an average of 15% but gave an earlier crop. Yield was reduced by up to 17% if irrigation at 40–60% of available moisture depletion in the first half of the season was followed by irrigation at 80% of available moisture depletion in the second half of the season. A rainfed treatment yielded from 16 to 43% less than the heaviest yielding irrigation treatment. After irrigation there was evidence of poor aeration in the soil which was most severe and lasted the longest at 30 cm depth. Heaviest yields were obtained with 100–150 kgN ha–1, except in rainfed treatments where 0–50 kgN ha–1 was sufficient. Irrigation at only 40% of available moisture depletion decreased nitrogen uptake in all seasons. Treatment effects on fibre quality in these experiments were small and variable. Nitrogen fertilizer generally increased length and strength but decreased micronaire. Stress during boll filling decreased micronaire and length in two of the four seasons.  相似文献   

12.
水肥耦合对棉花产量和氮累积利用的影响   总被引：2，自引：0，他引：2  
研究膜下滴灌施肥条件下,不同滴灌水量和滴灌施肥用量对棉花产量、氮素动态累积和氮素利用效率的影响。通过设置5个滴灌施肥水平和3个水分水平的完全组合处理以及一个不施肥对照处理,研究了水肥耦合对棉花干物质动态累积量、籽棉产量、氮动态累积量和氮素利用效率的影响。在收获后棉花地上部分器官质量从高到低依次为棉铃,茎秆和叶,而氮素主要集中在棉铃内部,其次是叶片,茎秆最少。灌溉水量显著增加了棉花叶片,茎秆和棉铃质量,从而增加了干物质量和籽棉产量,同时灌溉水量显著增加氮累积量和氮肥利用率。水肥对氮肥偏生产力,氮肥农学效率和氮肥生理利用率影响显著。灌溉水量降低至60%ETc会抑制棉花对氮素的吸收,使干物质量和籽棉产量下降,但可以显著提高氮肥利用率,氮肥偏生产力,氮肥农学效率。在本试验条件下,灌水量在380 mm,施肥量(N-P2O5-K2O)为(250-100-50)kg/hm2时,可以获得低于最高产量6%的籽棉产量,并节省15%的灌水量和16.7%施肥量。  相似文献   

13.
Summary The salt tolerance of irrigated Jerusalem artichokes (Helianthus tuberosus L.) was assessed in terms of biomass of both above ground parts and tubers in greenhouse and field trials. Salinity of irrigation water ranged from 0.7 to 12 dS m–1 in the greenhouse trial and from 0.2 to 10 dS m–1 in the field trial. Yield response of the dry matter of tubers of greenhouse-grown plants and of above ground parts of greenhouse-grown and fieldgrown plants, fell within the moderately tolerant category of Maas and Hoffman (1977). However, tuber yields in the field on a heavy clay loam fell within the moderately sensitive category, described by the equation, Y = 100 – 9.62 (ECe-0.4), where Y = yield (t ha–1) as a % of that under non-saline conditions and ECe = electrical conductivity of saturation extract in the rootzone (0–30 cm). The Cl concentration of leaves increased linearly with increasing external salinity and increased from tubers to stems to leaves. In contrast, leaf Na remained low except at the highest salinities, despite consistently higher stem Na; indicating some mechanism for restriction of leaf Na up to a certain external salinity.  相似文献   

14.
Summary Rapid drying of surface layers of coarse-textured soils early in the growth season increases soil strength and restricts root growth. This constraint on root growth may be countered by deep tillage and/or early irrigation. We investigated tillage and irrigation effects on root growth, water use, dry matter and grain yield of wheat on loamy sand and sandy loam soils for three years. Treatments included all combinations of two tillage systems i) conventional tillage (CT) — stirring the soil to 10 cm depth, ii) deep tillage (DT) — subsoiling with a single-tine chisel down to 35–40 cm, 40 cm apart followed by CT; and four irrigation regimes, i) I0 — no post-seeding irrigation, ii) I1 — 50 mm irrigation 30 days after seeding (DAS), iii) I2 — 50 mm irrigation 30 DAS and subsequent irrigations of 75 mm each when net evaporation from USWB class A open pan (PAN-E) since previous irrigation accumulated to 82 mm, and iv) I3 — same as in I2 but irrigation applied when PAN-E accumulated to 62 mm. The crop of wheat (Triticum aestivum L. HD 2329) was fertilized with 20kg P, 10kg K and 5kg Zn ha–1 at seeding. The rate of nitrogen fertilization was 60 kg ha–1 in the unirrigated and 120 kg ha–1 in the irrigated treatments. Tillage decreased soil strength and so did the early post-seeding irrigation. Both deep tillage and early irrigation shortened the time needed for the root system to reach a specified depth. Subsequent wetting through rain/irrigation reduced the rate of root penetration down the profile and also negated deep tillage effects on rooting depth. However, tillage/irrigation increased root length density in the rooted profile even in a wet year. Better rooting resulted in greater profile water depletion, more favourable plant water status and higher dry matter and grain yields. In a dry year, the wheat in the DT plots used 46 mm more water, remained 3.3 °C cooler at grain-fill and yielded 68% more grain than in CT when unirrigated and grown in the loamy sand. Early irrigation also increased profile water depletion, more so in CT than DT. Averaged over three years, grain yield in DT was 12 and 9% higher than in CT on loamy sand and sandy loam, respectively. Benefits of DT decreased with increase in rainfall and irrigation. Irrigation significantly increased grain yield on both soils, but the response was greatly influenced by soil type, tillage system and year. The study shows that soil related constraints on root growth may be alleviated through deep tillage and/or early irrigation.  相似文献   

15.
A field experiment was conducted for 2 years to investigate the effects of deficit irrigation, nitrogen and plant growth minerals on seed cotton yield, water productivity and yield response factor. The treatment comprises six levels of deficit irrigation (Etc 1.0, 0.9, 0.8, 0.7, 0.6 and 0.5) and four levels of nitrogen (80, 120, 160 and 200 kg N ha−1). These were treatments superimposed with and without plant growth mineral spray. Furrow irrigation treatments were also kept. Cotton variety Ankur-651 Bt was grown during 2006 and 2007 cotton season. Drip irrigation at 1.0 Etc saved 26.9% water and produced 43.1% higher seed cotton yield over conventional furrow irrigation (1.0 Etc). Imposing irrigation deficit of 0.8 Etc caused significant reduction in seed cotton yield to the tune of 9.3% of the maximum yield. Further increase in deficit irrigation from 0.7 Etc to 0.5 Etc significantly decreased seed cotton yield over its subsequent higher irrigation level. Decline in the yield under deficit irrigation was associated with reduction in number of bolls plant−1 and boll weight. Nitrogen at 200 kg ha−1 significantly increased mean seed cotton yield by 36.3% over 80 kg N ha−1. Seed cotton yield tended to increase linearly up to 200 kg N ha−1 with drip Etc 0.8 to drip Etc 1.0. With drip Etc 0.6-0.5, N up to 160 kg ha−1 provided the highest yield, thereafter it had declined. Foliar spray of plant growth mineral (PGM) brought about significant improvement in seed cotton yield by 14.1% over control. The water productivity ranged from 0.331 to 0.491 kg m−3 at different irrigation and N levels. On pooled basis, crop yield response factor of 0.87 was calculated at 20% irrigation deficit.  相似文献   

16.
The increasing scarcity of water for irrigation is becoming the most important problem for producing forage in all arid and semi-arid regions. Pearl millet is a key crop in these regions which needs relatively less water than other crops. In this research, a field study was conducted to identify the best combination of irrigation and nitrogen (N) management to achieve acceptable pearl millet forage both in quantity and quality aspects. Pearl millet was subjected to four irrigation treatments with interaction of N fertilizer (0, 75, 150 and 225 kg ha−1). The irrigation treatments were 40%, 60%, 80% and 100% of total available soil water (I40, I60, I80 and I100, respectively). The results showed that increasing moisture stress (from I40 to I100) resulted in progressively less total dry matter (TDM), leaf area index (LAI), and nitrogen utilization efficiency (NUzE), while water use efficiency (WUE) and the percentage of crude protein (CP%) increased. The highest TDM and LAI were found to be 21.45 t ha−1 and 8.65, in I40 treatment, respectively. TDM, WUE, CP% and profit responses to N rates were positive. The maximum WUE of 4.19 kg DM/m3 was achieved at I100 with 150 kg N ha−1. The results of this research indicate that the maximum profit of forage production was obtained in plots which were fully irrigated (I40) and received 225 kg N ha−1. However, in the situation which water is often limited and not available, application of 150 kg N ha−1 can produce high forage quality and guaranty acceptable benefits for farmers.  相似文献   

17.
Summary In a previous study conducted at the University of California at Riverside, it was shown that water use of cowpea could be reduced while maintaining seed yields by withholding irrigation during the vegetative stage in a rain-free environment, and then irrigating when estimates based on potential evapotranspiration, indicated 40% depletion of available moisture in 90-cm depth of soil. The general applicability of this efficient irrigation management method was tested by experiments conducted at the West Side Field Station in the San Joaquin Valley of California with six irrigation treatments, three different row spacings (single rows on 76- and 102-cm beds, and double rows on a 102-cm bed), a semi-erect cultivar of cowpea (Vigna unguiculata [L.] Walp.), and a prostrate cultivar of lima bean (Phaseolus lunatus L.).Withholding irrigation during the vegetative stage following pre-irrigation substantially reduced dry matter at anthesis (–17% to –38%) and water use (–101 mm) of cowpea, but did not influence seed yield or shoot dry matter at harvest for either cowpea or lima bean. Increasing the irrigation interval until 75% nominal depletion of available water in 90-cm depth of soil reduced water use (–139 cm), but did not affect seed yield of cowpea. Lima bean, however, showed a significant decrease in shoot dry matter production (–17%) and in seed production (–18%) at the longest irrigation interval involving 75% nominal depletion. The different row spacings used in this experiment did not affect shoot dry matter or seed production of the semi-erect cowpea. However, shoot dry matter and seed yield were significantly greater for the prostrate lima bean grown with double rows on a 102-cm bed. Seed yield was 46% and 18% greater than with single rows on 76-cm and 102-cm beds, respectively. Generally, variations in seed yields of lima bean were positively correlated with variations in shoot dry matter production.Nominal depletion of available soil water provided a practical method for scheduling irrigations, but the results with cowpea indicated that the critical level, which resulted in the greatest reductions in water use while maintaining maximum seed yield varied from 40% (at Riverside) to 75% (at West Side Field Station). Additional methods are needed to fine-tune irrigation which is based mainly on nominal depletion of available water. Generally, pressure chamber estimates of leaf water potential exhibited too little variation among plants subjected to different irrigation treatments for it to be useful for fine-tuning irrigation schedules for either cowpea or lima bean. However, differences in temperature between canopy and air, when expressed as a function of either vapor pressure deficit or canopy temperature, and related to percent reduction in yield, appeared to have sufficient resolution to provide a practical method for fine-tuning irrigation schedules for cowpea during flowering and pod-filling, but not lima bean. Normalizing temperature differences with vapor pressure deficit was more effective, but normalizing with canopy temperatures is more convenient because it does not require a measurement of air humidity.  相似文献   

18.
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.  相似文献   

19.
A study was conducted to determine the water stress effect on yield and some physiological parameters including crop water stress index for drip irrigated second crop watermelon. Irrigations were scheduled based on replenishment of 100, 75, 50, 25, and 0% soil water depletion from 90 cm soil depth with 3-day irrigation interval. Seasonal crop evapotranspiration (ET) for I100, I75, I50, I25, and I0 were 660, 525, 396, 210, and 70 mm in 2003 and 677, 529, 405, 221, and 75 mm in 2004. Fruit yield was significantly lowered by irrigation water stress. Average water-yield response factor for both of the years was 1.14. The highest yield was obtained from full irrigated treatment as 34.5 and 38.2 t ha−1 in 2003 and 2004, respectively. Lower ET rates and irrigation amounts in water stress treatments resulted in reductions in all measured parameters, except water-soluble dry matter concentrations (SDM). Canopy dry weights, leaf relative water content, and total leaf chlorophyll content were significantly lowered by water stress. Yield and seasonal ET were linearly correlated with mean CWSI values. An average threshold CWSI value of 0.17 before irrigation produced the maximum yield and it could be used to initiate the irrigation for watermelon.  相似文献   

20.
Yield and nitrogen use efficiency (NUE) of wheat was investigated under field conditions using two types of irrigation waters with and without nitrogen on a sandy-loam to loamy-sand soil during 1992–1993 and 1993–1994. Depending upon different nitrogen treatments, the mean crop yield ranges in 1992–1993 were: grain yield 6.19–6.87 Mg ha− and biomass 15.41–16.34 Mg ha−1 receiving treated effluent. The mean crop yield ranges in 1993–1994 were: grain yield 0.46–3.23 Mg ha−1 (well water) and 5.20–6.54 Mg ha−1 (treated effluent); and biomass 1.84–10.80 Mg ha−1 (well water), and 16.00–19.29 Mg ha−1 (treated effluent). The NUE for grain yield in 1992–1993 was between 16.70–50.23 kg kg−1 N (well water) and 20.65–91.56 kg kg−1 N (treated effluent). Whereas the NUE in 1993-94, varied between 10.49–32.13 kg grain kg−1 N (well water) and 21.30–72.93 kg grain kg−1 N (treated effluent). The NUE for total biomass in 1992–1993 varied between 46.54–130.32 kg kg−1 N (well water) and 53.66–158.77 kg kg−1 N (treated effluent). Similarly, the NUE in 1993–1994 varied between 35.99–102.1 kg biomass kg−1 N (well water) and 59.27–161.89 kg biomass kg−1 N (treated effluent). A significant decrease in NUE was observed with increasing nitrogen application both for grain and biomass production. In conclusion, a higher grain yield and NUE of wheat crop can be achieved with low application rates of nitrogen if the crop is irrigated with treated effluent containing nitrogen in the range of 20 mg L−1 and above.  相似文献   

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