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1.
Summary Effects of weekly (W) and fortnightly (F) irrigation schedules on CO2 assimilation by lucerne grown on untreated (C) and gypsum-ameliorated (G) heavy clay soil were investigated. Leaf area limited rates of assimilation during the initial stages of regrowth, but rates of up to 9 g CO2 m–2 h–1 were measured once full ground cover was achieved after approximately two weeks. High rates were maintained until the fifth week of regrowth (one week after full flower), after which there was a marked decline.During the fourth week of regrowth, afternoon rates of canopy photosynthesis under less frequent irrigation were less than those measured at similar irradiance during the morning. This was evidenced as hysteresis in the light response curves and was apparent in all treatment during the final stages of the experiment.For the first five weeks of regrowth, daytime integrals of photosynthesis were directly related to the amount of light intercepted by the crops. The mean efficiency of utilisation of light in CO2 assimilation was 6.2 g CO2 MJ–1 in all treatments apart from that on untreated soil under the fortnightly irrigation regime (treatment FC). Its mean efficiency was 5.1 g CO2 MJ–1. The amounts of CO2 assimilated exceeded the growth and respiratory requirements of the above-ground components of the crops, and it was estimated that 25% and 40% of the assimilated carbon was partitioned to and retained in the roots and crowns of the weekly and fortnightly irrigated crops, respectively.Results are appraised in terms of the response of lucerne to moisture deficits. Implications for above-ground dry matter production are also discussed.  相似文献   

2.
Summary Several irrigation management experiments were conducted at different locations on sandy soils in Haryana State to overcome excessive permeability, poor soil moisture retention and storage in the root zone. Subsurface compaction to 30–40 cm depth created by 6 passes of a 1,500 kg tractor-driven iron roller, 24 to 48 h after irrigation, was found to be beneficial in reducing irrigation requirement. In general, yield of different crops was not affected significantly by surface rolling, except that of mustard which increased significantly. Slight increase in subsurface compaction, about 0.1 g cm–3, increased the soil moisture retention and reduced the infiltration rate and saturated hydraulic conductivity. Hydraulic conductivity was a better parameter than bulk density for evaluating the effect of rolling. The depth of irrigation water applied in rolling treatment was about 58–74% that of the no-rolling control. Compaction thus reduced water input to these sandy soils without adversely affecting the crop yield.  相似文献   

3.
Production and water use in lettuces under variable water supply   总被引：3，自引：0，他引：3  
The effects of a variable water supply on the water use, growth and yield of two crisphead and one romaine (i.e., Cos) lettuce cultivar were examined in a field experiment using a line source sprinkler system that produced a range of water regimes that occur in growers fields. Four locations at increasing distances from the main line were monitored through the season (i.e., from thinning to harvest, 28–63 days after planting (DAP)). These locations at the end of the season corresponded to: (1) rewatering to field capacity (FC); (2) watering with a volume 13% below that required in the field capacity treatment (0.87*FC); (3) 30% below FC (0.70*FC); and (4) 55% below FC (0.45*FC). A linear production function for dry matter accumulation and fresh weight vs. crop evapotranspiration (ETc) was determined for lettuce during this period, giving a water use efficiency for dry matter of 1.86 g m–2 mm–1 and for fresh weight of 48 g m–2 mm–1 . For lettuce irrigated to field capacity, ETc between thinning and harvest was 146 mm; maximum crop coefficients of 0.81–1.02 were obtained at maturity (55–63 DAP). For the three irrigation treatments receiving the largest water application, ETc was higher in the Cos culivar than in the two crisphead lettuce cultivars which had similar ETc. Plant fresh weight was more sensitive than dry weight to reduction in water supply. In the FC treatment, root length density and soil water extraction were greatest in the top 0–45 cm, and decreased rapidly below 45 cm depth. Soil water extraction by roots increased at lower depths when irrigation was reduced. Instantaneous rates of leaf photosynthesis and leaf water potential showed no response to the irrigation treatments in this study, despite differences in biomass production. Evaporation was determined to be the major component of ETc for 45 of the 63 days of the growing season. The large loss of water by evaporation during mid-season and the apparent insensitivity of lettuce to the volume of irrigation during this period may provide an opportunity for reducing irrigation applications.  相似文献   

4.
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   

5.
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, ma) 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 ma 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 ma. 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 ma at maturity. The study indicates that Δ and ma can be used as indirect selection criteria for grain yield and suggests that ma 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 ma across cultivars and evaluate the possibility to use these traits as predictors of WUE in wheat breeding programs.  相似文献   

6.
Summary Concurrent diurnal measurements of water potential, osmotic potential and conductance were made on leaves of lucerne grown under weekly (W) and fortnightly (F) irrigation on gypsum-treated (G) and untreated soil (C). Measurements were made throughout the period of vegetative growth.Leaf water potentials were lower both at dawn and in the afternoon under fortnightly as compared to weekly irrigation. Gypsum application led to a slower decline in water potential under fortnightly irrigation, although the effect was small compared with more frequent irrigation. Stomatal conductance was reduced under treatments FG and FC during the later stages of vegetative growth, coinciding with leaf water potentials of less than c. –1.6 MPa.The relationship between leaf water potential and turgor potential changed with time such that positive turgor was maintained as leaf water potential declined. Turgor maintenance was achieved through a decrease in leaf osmotic potential. These data suggest that lucerne is capable of osmotic adjustment.Stomatal conductance declined rapidly below a leaf turgor potential of c. 0.1 MPa. It is hypothesised that osmotic adjustment enabled stomatal adjustment, which contributed to continued assimilation despite increasing soil moisture deficits.  相似文献   

7.
The effect of watering up to approximately 100% of volumetric available soil water on total biomass, nitrogen (N) balance, and market yield of broccoli crops (Brassica oleracea L. convar. botrytis var. italica Plenck, cv. Emperor) was studied. The experiment was carried out in a microplot field installation on two soil types (alluvial loam and loessal loam) under spring and autumn cultivation and consisted of three soil water regimes: plants received 21 mm of water by irrigation until the soil moisture reached 75% of the available soil water (ASW), treatment 1; 42 mm after the soil moisture reached 55% ASW, treatment 2; and 63 mm after the soil moisture reached 35% ASW, treatment 3. The ASW of the three treatments was measured at a depth of 0.15 m. The total plant mass was significantly affected by the irrigation strategy on the loessal loam in spring and on the alluvial loam in autumn. The total mass and head mass were lowest when water was applied at 75% ASW in spring and autumn. Calculations of N-balances showed that N losses were large, i.e. more than 70 kg·ha–1 in spring and 130 kg·ha–1 in autumn on the alluvial loam in treatment 1, and were only slightly affected by the irrigation strategy on the loessal loam.Communicated by R. Evans  相似文献   

8.
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   

9.
Summary Dry-seeded rice (Oryza sativa L., cv. Calrose) was subjected to 4 irrigation treatments — continuous flood (CF) and sprinkler irrigation at frequencies of one (S1 W), two (S2W) and three (S3W) applications per week — commencing 37 d after 50% emergence (DAE). The amount of water applied was calculated to replace water lost by pan evaporation. Urea (120 kg N ha–1) was applied in a 1:1 split 36 and 84 DAE, and there were also unfertilized controls for each irrigation treatment. Amounts of nitrate (NO 3 – ) in the soil were very low throughout the growing season in all treatments, despite regular periods of draining which lasted for up to 7 d in SlW. In all irrigation treatments, the majority of the fertilizer nitrogen (N) was located in the top 20 mm of soil. After each application of fertilizer, levels of mineral N in CF declined rapidly, while levels in S3W and S1W remained high for 1–2 weeks longer. The poor growth of sprinkler-irrigated rice was not due to lower amounts of mineral N in the soil. The greater persistence of fertilizer N in the sprinkler-irrigated treatments was probably due to reduced root activity near the soil surface because of frequent periods of soil drying in between irrigations. Net mineralization of soil N in the unfertilized sprinkler-irrigated treatments was reduced by about half compared with CF.On average, the quantity of water applied (1.2–1.4 × EP) to the sprinkler-irrigated treatments appeared to be sufficient to meet the evapotranspiration demands of the crop, except possibly around flowering time. However, the plants may have suffered from moisture stress in between irrigations. Soil matric potential data at 100 mm suggested little water stress in the sprinkler-irrigated treatments during the vegetative stage, consistent with the similar tiller and panicle densities in all irrigation treatments. However, the crop was stunted and yellow and leaf rolling was observed in the sprinkler-irrigated treatments during this period. Soil matric potential data at 100 mm indicated considerable water stress in S1W beyond the commencement of anthesis, and in S2W during grain filling, consistent with the reduced floret fertility and grain weight in those treatments.  相似文献   

10.
Summary An irrigation experiment with water of different salinities (2.8, 7.6 and 12.7 mol Cl m–3) was carried out from 1982 to 1988 in a mature Shamouti orange grove in the coastal plain of Israel. Seasonal accumulation of salts in the soil solution of the root zone (EC of more than 4.0 dS m–1 at the end of the irrigation season) was almost totally leached during the winter. The average annual rainfall of 550 mm reduced EC values below 1.0 dS m–1. Tree growth, as measured by the increase in cross sectional area of main branches, was retarded by saline irrigation water (123, 107 and 99 cm2 growth per tree during six years for the 2.8, 7.6 and 12.7 mol Cl m–3 treatments, respectively). Potassium fertilization (360 kg K2O ha–1) increased yield at all salinity levels during the last three years of the experiment, mainly by increasing fruit size. Saline irrigation water slightly increased sucrose and C1 concentrations in the fruit juice. Salinity decreased transpiration, increased soil water potential before irrigation and decreased leaf water potential. However, the changes in leaf water potential were small. Leaf Cl and Na concentrations increased gradually during the experimental period, but did not reach toxic levels up to the end of the experiment (4.4 g Cl kg–1 dry matter in the high salt treatment vs. 1.7 in the control). Relatively more leaf shedding occurred in the salinized trees as compared to the control. The sour orange root-stock apparently provided an effective barrier to NaCl uptake; therefore, the main effect of salinity was probably osmotic in nature. No interactions were found between N or K fertilization and salinity. Additional N fertilization (160 kg N ha–1 over and above the 200 kg in the control) did not reduce Cl absorption nor did it affect yield or fruit quality. Additional K had no effect on Na absorption but yield and fruit size were increased at all salinity levels. No significant differences were obtained between partial and complete soil surface wetting (30% and 90% of the total soil area resp.) with the same amounts of irrigation water. The effect of salinity on yield over the six years of the experiment was relatively small and occurred only after some years. But, in the last three years salinity significantly reduced average yields to 74.6, 67.1, and 64.2 Mg ha–1 for the three levels of salinity, respectively.These results suggest that saline waters of up to 13 mol Cl m–3 primarily influence the tree water uptake and growth response of Shamouti orange trees, whereas yield was only slightly reduced during six years.  相似文献   

11.
Summary A laboratory study was conducted to investigate the effect of gel-forming conditioner (Jalma) at rates of 0.0, 0.2, 0.4 and 0.8% at four depths of gel-conditioned barriers: 0–0.05, 0.10–0.15, 0.15–0.20 and 0.20–0.25 m, on infiltration, intermittent evaporation, water conservation and soil moisture distribution for calcareous sandy soil (Typic Torripsamments) at two moisture regimes. Addition of 0.8% Jalma on surface significantly increased the time required for 50 mm to infiltrate (t50) into the soil. However, with deeper subsurface barriers the rate of Jalma application had no significant affect on t50 for the first cycle. Time required for 50 mm to infiltrate for any Jalma rate increased with the number of irrigation cycles due to cumulative increase of moisture of soil columns. The times required for 100 mm to infiltrate (t100) increased with increased rate of Jalma application and decreased with the depth of the treated barrier. Surface treatment significantly reduced cumulative evaporation and thus increased the amount of water conserved (PWC). Sub-surface Jalma-treated barriers promoted evaporation and hence reduced the amount of water conserved. Soil moisture profile of the columns showed that Jalma-treated barriers may be used to establish zones of maximum water storage at various depths in a sand profile.  相似文献   

12.
The ability of cotton roots to grow downwards through a partially-wetted soil (Calcic Haploxeralf) profile toward a water source located beneath them was investigated. Plants were grown in 60-cm-high soil columms (diameter 10 cm), the bottom 15 cm of which was kept wet by frequent drip irrigation, while the upper 45 cm was wetted three times per week up to 20, 40, 60, 80 or 100% of pot capacity. Pot capacity was defined as the water content which gave uniform distribution within the pot and was at a soil matric potential ( m ) of –0.01 MPa. Plants were harvested 42 and 70 days after emergence (DAE). Root length density was reduced by decreased soil moisture content. At 42 DAE, density was reduced in the soil profile down to 36 cm. The density in the middle segment of the cylinder (24–36 cm) increased at the second harvest, from 0.1 to 0.35 cm · cm–3 at 40% and from 0.2 to 0.5 cm · cm–1 at 60% of pot capacity, respectively. A significant rise in root length density was found at all moisture contents above 20% in the two deepest soil segments. It was most marked at 40% where the rise was from 0.2 to 0.8 cm · cm–3, due to the development of secondary roots at the wetted bottom of the column. When only 20% of pot capacity was maintained in the top 45 cm of the profile, almost no roots reached the wetted soil volume, and root length density was very low. Hydrotropism, namely root growth through dry soil layers toward a wet soil layer was thus not apparent. Root dry weight per unit length decreased with increasing depth in the column at all moisture levels. However, the only significant decrease was, found between the top and the second soil segments and was due to thicker primary roots in the top segment. There was no clear relationship between length and dry weight of roots. Total plant dry weight and transpiration were reduced significantly only at 20% of pot capacity. Dry matter production by roots was less severely inhibited than that by shoots, under decreased moisture content in the soil profile. Leaf water potential decreased when the soil moisture content of the top 45 cm of the profile was reduced below 60% of pot capacity. It was concluded that even at soil moisture content equivalent to a m of 0.1 MPa, the rate of root growth was sufficient to reach a wetted soil layer at the bottom of the soil column, where the plant roots then proliferated. This implies that as long as the soil above the subsurface dripper is not very dry there is no real need for early surface irrigation.  相似文献   

13.
Summary A coupled soil-vegetation energy balance model which treats the canopy foliage as one layer and the soil surface as another layer was validated againt a set of field data and compared with a single-layer model of a vegetation canopy. The two-layer model was used to predict the effect of increases in soil surface temperature (T s ) due to the drying of the soil surface, on the vegetation temperature (T v ). In the absence of any change in stomatal resistance the impact of soil surface drying on the Crop Water Stress Index (CSWI) calculated from T v was predicted. Field data came from a wheat crop growing on a frequently irrigated plot (W) and a plot left un watered (D) until the soil water depletion reached 100 mm. Vegetation and soil surface temperatures were measured by infrared thermometers from tillering to physiological maturity, with meteorological variables recorded simultaneously. Stomatal resistances were measured with a diffusion porometer intensively over five days when the leaf area index was between 5 and 8. The T v predicted by the single-layer and the two-layer models accounted for 87% and 88% of the variance of measured values respectively, and both regression lines were close to the 11 relationship. Study of the effect of T s on the CWSI with the two-layer model indicated that the CWSI was sensitive to changes in T s . The overestimation of crop water stress calculated from the CWSI was predicted to be greater at low leaf area indices and high levels of stomatal resistance. The implications for this bias when using the CWSI for irrigation scheduling are discussed.List of Symbols C Sensible heat flux from the soil-vegetation system (W m–2) - c l shade Mean stomatal conductance of the shaded leaf area (m s–1) - c l sun Mean stomatal conductance of the sunlit leaf area (m s–1) - c max Maximum stomatal conductance (m s–1) - c 0 Minimum stomatal conductance (m s–1) - C p Specific heat at constant pressure (J kg–1 °C–1) - C s Sensible heat flux from the soil (W m–2) - C v Sensible heat flux from the vegetation (W m–2) - c v Bulk stomatal conductance of the vegetation (m s–1) - CWSI Crop Water Stress Index (dimensionless) - e a Vapor pressure at the reference height (kPa) - e b Vapor pressure at the virtual source/sink height of heat exchange (kPa) - e 0 * Saturated vapor pressure at T 0 (kPa) - e s Vapor pressure at the soil surface (kPa) - e v * Saturated vapor pressure at T v (kPa) - G Soil heat flux (Wm–2) - GLAI Green leaf area index (dimensionless) - GLAIshade Green shaded leaf area index (dimensionless) - GLAIsun Green sunlit leaf area index (dimensionless) - k Extinction coefficient for photosynthetically active radiation (dimensionless) - k 1 Damping exponent for Eq. A 5 (m2 W–1) - LAI Leaf area index (dimensionless) - LE Latent heat flux from the soil-vegetation system (W m–2) - LE s Latent heat flux from the soil (W m–2) - LE v Latent heat flux from the vegetation (W m–2) - p a Density of air (kg m–3) - PARa Photosynthetically active radiation above the canopy (W m–2) - PARu Photosynthetically active radiation under the canopy (W m–2) - r a Aerodynamic resistance (s m–1) - r b Heat exchange resistance between the vegetation and the adjacent air boundary layer (s m–1) - r c Bulk stomatal resistance of the vegetation (s m–1) - R n Net radiation above the canopy (W m–2) - R s Net radiation flux at the soil surface (W m–2) - r st Mean stomatal resistance of leaves in the canopy (s m–1) - R v Net radiation absorbed by the vegetation (W m–2) - r w Heat exchange resistance between the soil surface and the boundary layer (s m–1) - S Photosynthetically active radiation on the shaded leaves (W m–2) - S d Diffuse photosynthetically active radiation (W m –2) - S 0 Photosynthetically active radiation on a surface perpendicular to the beams (W m–2) - T a Air temperature at the reference height (°C) - T b Temperature at the virtual source/sink height of heat exchange (°C) - T 0 Aerodynamic temperature (°C) - T s Soil surface temperature (°C) - T v Vegetation temperature (°C) - w 0 Single scattering albedo (dimensionless) - Psychrometric constant (kPa °C) - 0 Cosine of solar zenith angle (dimensionless)  相似文献   

14.
Atmospheric CO2 enrichment may bring different effects on plant growth and evapotranspiration if plants are under N and water deficient conditions. In this study, spring wheat (Triticum aestivum L.) was grown in pots at two atmospheric CO2 concentrations (ambient and elevated), two levels of soil moisture (well-watered and droughted to 45–60% of field capacity) and five nitrogen (N) fertilization treatments (0, 112.5, 225.0, 337.5, 450.0 kg hm−2) in growth chambers. Leaf growth, leaf area, and tiller increment were largely a function of N application and water supply. Elevated CO2 increased 23–45% in leaf area only with the N-added treatments 55 days after sowing. Elevated CO2 also reduced stomatal conductance more in droughted treatments (−51%) than in well-watered treatments (−41%), and more with zero N application (−60%) than with the adequate N (−35 to 44%). Evapotranspiration (ET) was also reduced by CO2 enrichment in a similar way. Our results showed that the CO2-enrichment-induced decrease in transpiration almost compensated for the increase in ET brought by the higher leaf area under adequate N and water supply, such that ET was similar for control and CO2-enriched plants. Under reduced N and water supply, CO2 enrichment had limited effect on either leaf growth or ET.  相似文献   

15.
Summary A simplified method of estimating actual evapotranspiration of crops during an irrigation interval in which soil-moisture deficits occur is presented. With some simplifying assumptions, a relation is developed between a crop-dependent critical leaf water potential, potential evapotranspiration rates, and the fraction of available soil-moisture at which reduction in evapotranspiration occurs (Fig. 1). This relation was tested by comparing calculated and measured rates of actual evapotranspiration for maize, alfalfa, sorghum, wheat, potato, and sorghum crops (Fig. 2, A through F). Calculated values of actual crop water use were close to measured ones, except for the potato crop. Sensitivity tests indicated that, for crops with a critical leaf water potential above –7.5 bars, i.e. –0.75 MPa, errors exceeding 10 per cent were made in estimating the fraction of available soil moisture at which reduction in evapotranspiration occurs.  相似文献   

16.
The reported study aimed at developing an integrated management strategy for irrigation water and fertilizers in case of wheat crop in a sub-tropical sub-humid region. Field experiments were conducted on wheat crop (cultivar Sonalika) during the years 2002–2003, 2003–2004 and 2004–2005. Each experiment included four fertilizer treatments and three irrigation treatments during the wheat growth period. During the experiment, the irrigation treatments considered were I1 = 10% maximum allowable depletion (MAD) of available soil water (ASW); I2 = 40% MAD of ASW; I3 = 60% MAD of ASW. The fertilizer treatments considered in the experiments were F1 = control treatment with N:P2O5:K2O as 0:0:0 kg ha−1, F2 = fertilizer application of N:P2O5:K2O as 80:40:40 kg ha−1; F3 = fertilizer application of N:P2O5:K2O as 120:60:60 kg ha−1 and F4 = fertilizer application of N:P2O5:K2O as 160:80:80 kg ha−1. In this study CERES-wheat crop growth model of the DSSAT v4.0 was used to simulate the growth, development and yield of wheat crop using soil, daily weather and management inputs, to aid farmers and decision makers in developing strategies for effective management of inputs. The results of the investigation revealed that magnitudes of grain yield, straw yield and maximum LAI of wheat crop were higher in low volume high frequency irrigation (I1) than the high volume low frequency irrigation (I3). The grain yield, straw yield and maximum LAI increased with increase in fertilization rate for the wheat crop. The results also revealed that increase in level of fertilization increased water use efficiency (WUE) considerably. However, WUE of the I2 irrigation schedule was comparatively higher than the I1 and I3 irrigation schedules due to higher grain yield per unit use of water. Therefore, irrigation schedule with 40% maximum allowable depletion of available soil water (I2) could safely be maintained during the non-critical stages to save water without sacrificing the crop yield. Increase in level of fertilization increases the WUE but it will cause environmental problem beyond certain limit. The calibrated CERES-wheat model could predict the grain yield, straw yield and maximum LAI of wheat crop with considerable accuracy and therefore can be recommended for decision-making in similar regions.  相似文献   

17.
Summary The effects of frequent and shallow soil wetting by surface drip irrigation on root growth, morphology, and location, and their impact on plant sensitivity to irrigation management were studied in cotton (Gossypium hirsutum L.). Daily drip irrigation, which wetted the 0 to 40-cm soil depth, encouraged root development mainly around the drippers. Water extraction took place mostly from 0 to 20 cm below the drippers, where the roots were concentrated. Shallowness of root growth was not altered by the expansion and deepening of the wetted soil zone which resulted from an increase in amount of irrigation water. The shallow and restricted root system was characterized by a high fraction of thin roots (less than 1 mm dia.) which comprised almost 90% of the root dry matter. Root proximity to the drippers and the limited amount of water in the rooted soil led to a sensitive and quick response of the plants to small amounts of irrigation. A supply of 1.0 mm H2O given at midday to 70 day-old plants resulted in a leaf water potential (L w) increase from –1.64 to –1.32 MPa over a 20-min period. This amount of irrigation comprised 15% of the average daily quantity. A 24 h delay in irrigation to 80 dayold plants was enough to decrease L w from –1.41 to –2.42 MPa. This decrease was caused by a soil water deficit of less than 6 mm H2O. Extending the irrigation delay to 72 h affected yield and earliness, although the deficient amount of water was supplied over the several days after the treatment. A strong response to minor, but continuous, differences in the daily irrigation amount was detected. Differences in irrigation of less than 1 mm H2O per day applied during the whole growth season substantially affected L w, yield and earliness. It was concluded that the establishment of a shallow and restricted root system resulted in strong dependence of the plants on frequent and sufficient supply of water, and temporary minor changes in irrigation affected plant water status and productivity.  相似文献   

18.
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   

19.
Summary A neutron moisture meter was field calibrated in a cracking grey clay prepared for furrow irrigation at Narrabri, N.S.W. Neutron counts were taken in successive 0.1 m increments between the 0 and 1.5 m depths. Concomitant measurements using undisturbed soil cores provided independent estimates of volumetric water content. Separate linear calibrations were required for the 0–0.1 m, 0.1–0.2 m and 0.2–1.5 m depth increments. Correction for bias due to cracking and changes in bulk density slightly improved the calibrations. The accuracy of predicted soil water content was improved relative to previous calibrations. A precision of ±0.01 m3m–3 required 3 samples per mean by the neutron method or 11 samples per mean by the core sampling method.  相似文献   

20.
In irrigated agriculture, the production of biomass and marketable yield depend largely on the quantity and salinity of the irrigation water. The sensitivity of field-grown muskmelon (Cucumis melo L. cv. Galia) to water deficit was compared, using non-saline (ECi= 1.2 dS m–1) and saline (ECi=6.3 dS m–1) water. Drip irrigation was applied at 2-day intervals at seven different water application rates for each water quality, including a late water-stress treatment. Neutron scattering measurements showed that the soil layers below the root zone remained dry throughout the experiment, indicating negligible deep percolation. Thus, the sum of the seasonal amount of applied water and the change in soil moisture approximated the cumulative evapotranspiration (ET). Gradual buildup of water and salt stresses resulted in small treatment effects on the size of the vegetative cover and large effects on leaf deterioration and fruit production. Crop responses to salinity may result from an osmotic component of the soil water potential or from other salt effects on the crop physiology. Relating plant data to cumulative ET allowed a distinction to be made between the effect on water availability and specific salinity effects. The relation between fruit fresh weight and ET was not sensitive to ECi. The slopes for fruit dry weights were also insensitive to ECi but the intercept was larger for saline treatments. At any given ET saline water increased fruit number, increased fruit dry matter content and decreased fruit netting, in comparison with non-saline water. The combination of salinity and soil-water deficit was detrimental to fruit quality. Saline soil-water deficit decreased the percentage of marketable (netted) fruit and caused an early end to the period of marketable fruit production. Non-saline soil-water deficit increased the percentage of marketable fruit and had no effect on the duration of the production period. Late non-saline water stress caused a pronounced increase in the percentage of marketable fruit.  相似文献   

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