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1.
Recent community based actions to ensure the sustainability of irrigation and protection of associated ecosystems in the Murrumbidgee Irrigation Area (MIA) of Australia has seen the implementation of a regional Land and Water Management Plan. This aims to improve land and water management within the irrigation area and minimise downstream impacts associated with irrigation. One of the plan objectives is to decrease current salt loads generated from subsurface drainage in perennial horticulture within the area from 20 000 tonnes/year to 17 000 tonnes/year. In order to meet such objectives Controlled Water table Management (CWM) is being investigated as a possible ‘Best Management Practice’, to reduce drainage volumes and salt loads.During 2000–2002 a trial was conducted on a 15 ha subsurface drained vineyard. This compared a traditional unmanaged subsurface drainage system with a controlled drainage system utilizing weirs to maintain water tables and changes in irrigation scheduling to maximize the potential crop use of a shallow water table. Drainage volumes, salt loads and water table elevations throughout the field were monitored to investigate the effects of controlled drainage on drain flows and salt loads.Results from the experiment showed that controlled drainage significantly reduced drainage volumes and salt loads compared to unmanaged systems. However, there were marked increases in soil salinity which will need to be carefully monitored and managed.  相似文献   

2.
Summary The energy requirements for manufacturing irrigation equipment were evaluated from a survey of a number of factories and workshops in Israel.Based on the results obtained and the life span of the components, the annual amortization of energy by high-pressure (overhead sprinklers), medium-pressure (undertree sprinklers and sprayers) and low-pressure (drip lines) irrigation systems was calculated for citrus orchards and cotton crops as irrigated in Israel. For citrus orchards a low-pressure sprayer system amortized 1.5 GJ ha–1 y–1 more energy than a medium-pressure undertree sprinkler system, and 2.7 GJ ha–1 y–1 more than a high-pressure, overhead sprinkler system. For irrigating a cotton crop, the low-pressure drip system used 6.8 GJ ha–1 y–1 more embodied energy than the movable, high-pressure overhead sprinkler system.The annual energy invested in irrigation water conveyance through the National Water Carrier, at the current hydraulic pressure of 500 kPa at the farm gate, varies for a cotton crop from 20 to 45 GJ ha–1 y–1 in the northern region and from 70 to 215 GJ ha–1 y–1 in the southern region of Israel, when irrigated with 4,050 m3 ha–1. For a citrus orchard this energy input varies from 60 to 75 GJ ha–1 y–1 in the central region and from 120 to 375 GJ ha–1 y–1 in the southern regions, when irrigated with 7,200 m3 ha–1. For obtaining the same yield in the south as in the north, the energy input for water conveyance has to be increased by 12% in the case of a cotton crop and by 7% in the case of a citrus orchard. Thus, in the north the annual energy amortization of a dripline irrigation system amounts to one third of that expended on water conveyance but in the south amounts to one-eighteenth or less, indicating the large regional dependency of energy inputs for irrigation.Calculations show that the reduction in energy requirement for water conveyance needed by irrigation systems operating at lower pressures compensates for their higher energy losses in system amortization. For example, in citrus irrigation the substitution of medium-pressure undertree sprinkler systems for high-pressure overhead sprinkler systems was calculated to save 8% of the total energy expenditure for water conveyance to the farm gate. This would amount to a saving of 7 GJ ha–1 y–1 for citrus in the central region and of 8 GJ ha–1 y–1 in the south. For cotton the substitution of low pressure dripline systems for high-pressure overhead sprinkler systems could save 16% of the total energy expenditure for pressurized water conveyance. This would amount to a saving of 8 GJ ha–1 y–1 in the northern region increasing to 10 GJ ha–1 y–1 in the south, taking into account a higher irrigation water requirement.Contribution from the Agricultural Research Organization, Bet Dagan, Israel. No. 1589-E, 1985 series  相似文献   

3.
Actual evapotranspiration (ETc) of three mature sweet orange orchards (cv. Salustiana and Washington Navel on sour orange), under border irrigation and typical cultural practices was measured by the water balance method during 1981 to 1984. Soil water content was measured at 7 to 10 day intervals using a neutron meter and soil sampling of the 0–10 cm surface layer. Zero flux plane was calculated by measurements with mercury tensiometers. Irrigation water in these and other 5 similar orchards was measured by broad crested weirs. Rainfall and other climatic data for calculation of reference evapotranspiration by FAO's methods (ETo) were collected in a nearby meteorological station. Average yearly ETc ranged from 750 to 660 mm and mean monthly maximum was 3.7 and 3.2 mm/day in July for Salustiana and W. Navel orchards, respectively.ETo estimates for the different methods used were highly correlated (r 20.94). Monthly crop coefficients (Kc) based on pan evaporation ranged from 0.5–0.6 in spring and summer to 0.8 in autumn and were about 10% higher than those for Penman or radiation methods. Average annual Kc for the three plots studied was 0.64, 0.61 and 0.51, respectively, and correlated well (r 2=0.99) with tree ground cover. Irrigation efficiency was about 50% for orchards with soils with less water holding capacity and more applied water per irrigation and 70–80% in orchards with deeper soils or with a higher water holding capacity. Increasing irrigation frequency and applying smaller amounts of water per irrigation with good uniformity can improve on-farm irrigation efficiency.  相似文献   

4.
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   

5.
Irrigation of Lucerne under semi-arid conditions in Cyprus   总被引：1，自引：0，他引：1  
Summary Three amounts of water –1.0, 0.8 and 0.6 of the irrigation requirement — were used to irrigate lucerne at two frequencies of application — once or twice during each growth cycle. Screened Class A pan evaporation, adjusted by monthly crop coefficients, proved a dependable guide for irrigation. Irrigating once per growth cycle was sufficient, and the highest yield was obtained when the full irrigation requirement was applied. The average annual dry matter yield for the three amounts of irrigation water — 1390, 1110 and 829 mm per year — was 20 285, 16 353 and 12 952 kg ha–1 respectively, i. e., yield decreased linearly with decreasing amount of water applied. As the water used was saline — with an electrical conductivity of 3 mmhos/cm–1 — the main root zone became gradually salinized with the drier treatments, while with the wettest treatment salts accumulated below 80 cm depth. Yields were drastically reduced during the hot summer months, even when adequate water was available in the soil profile. This combined with the high irrigation requirement resulted in very low efficiency of irrigation during summer.  相似文献   

6.
Economic incentives reduce irrigation deliveries and drain water volume   总被引：1，自引：0，他引：1  
This paper describes the application of an economic incentive program to achieve water quality objectives by motivating improvements in farm-level water management practices. The program includes farm-specific water allotments, tiered water pricing, and low-interest loans for purchasing irrigation equipment. The implementation of this program in a California water district has resulted in significant reductions in irrigation deliveries and drain water volume. Since the program was implemented, average irrigation depths have declined by 25% on cotton fields, 9% on tomatoes, 10% on cantaloupes, 30% on seed alfalfa, and 29% on grain fields. The average volume of drain water collected each year in subsurface drainage systems has declined from 4.8 million m3 during 1986 through 1989 to 2.6 million m3 during 1990 through 1993. These results confirm that economic incentives can be effective in generating improvements in water quality.  相似文献   

7.
Water use efficiency of irrigated wheat in the Tarai region of India   总被引：1，自引：0，他引：1  
Experiments were conducted during the winter seasons of 1983–1984 and 1984–1985 to identify suitable irrigation regimes s for wheat grown after rice in soils with naturally fluctuating shallow water table (SWT) at a depth of 0.4 to 0.9 m and medium water table (MWT) at a depth of 0.8 to 1.3 m. Based on physiological stages, the crop was subjected to six irrigation regimes viz., rainfed (I0); irrigation only at crown root initiation (I1); at only crown root initiation and milk (I2); at crown root initiation, maximum tillering and milk (I3); at crown root initiation, maximum tillering, flowering and milk (I4); and at crown root initiation, maximum tillering, flowering milk and dough (I5). Tube-well water with an EC <0.4 dsm–1 was used for irrigation. Based on 166 mm effective precipitation during the cropping season, 1983–1984 was designated as a wet year and 1984–1985 with 51 mm as a dry year. The change in profile soil water content W (depletion) in the wet year was less (23%) under SWT and 10% under MWT as compared to the dry year. The ground water contribution (GWC) to evapotranspiration (ET) was 58% under SWT and 42% under MWT conditions in both the years. The GWC in the wet year was 20% under SWT and 23% under MWT. Of the total net water use (NWU), about 85% was ET and 15% drainage losses. The NWU was highest (641 and 586 mm) in I5 under SWT and MWT conditions, respectively, but not the yield (5069 kg ha–1). Compared to I5, NWU in I2 treatment decreased by 10% in the wet and 25% in the dry year. A similar trend was observed in the I3 treatment under MWT condition. However, there was no statistically significant difference between yields of the I1 to I5 treatments of either water table depth during the wet year. This was also true during the dry year for the I2 to I5 treatments. Under SWT, in I2, the grain yield was 5130 kg ha–1 and under I3 regime, 5200 kg ha–1. Under MWT in I3, the yield was 5188 kg ha–1 and under I4 regime, 5218 kg ha–1. Thus it appears that in the Tarai region where the water table remains shallow (<0.9 m) and medium (<1.3 m) for most of the wheat growing season applications of more than 120 and 180 mm irrigation under SWT and MWT conditions, respectively were not necessary. Irrigation given only at crown root initiation and milk stages under shallow water table conditions, and at crown root initiation, maximum tillering and milk stages under medium water table conditions, appears to be as effective as frequent irrigations.  相似文献   

8.
Summary The mean velocity at which water flowed through large undisturbed cores of soil was determined from the breakthrough of surface-applied Cl–, using a transfer function based on the normal distribution of the logarithm of cumulative drainage. For soils ranging in texture from sandy loam to silty clay loam, mean pore water velocities varied from 7 to 30 cm h–1 for an input rate of 2 cm h–1. Antibiotic-resistant Escherichia coli applied to the soil surface appeared to be transported through large pores only (> 10–15 m diameter), and the relative concentration in the effluent (C/C0) did not change significantly with effluent volume. Mean C/C0 values for E. coli in these soils, which ranged from 0.003 to 0.94, could be predicted from the mean pore water velocity derived from Cl– transport.  相似文献   

9.
Summary In this paper the soil water balance model developed and tested in Part III (Mason and Smith, 1980) for soybeans grown in the variable rainfall environment of the Namoi Valley of New South Wales was used to investigate the potential advantages of a computer-based system of irrigation scheduling. The advantages were evaluated using historical rainfall data for the 25 seasons from 1953/54 to 1977/78. The effects on irrigation efficiency of soil water holding capacity, the allowable soil water deficit prior to irrigation, and ordering irrigation water in advance were evaluated with the model. Reducing the allowed deficit prior to irrigation by 20% compared to the recommended level increased the number of irrigations by an average of 2.8 per year and irrigation requirements by 0.73 X 103 m3 ha–1. The need to order water 6 days in advance because of delays in delivery also increased requirements by 1.46 X 103 m3 ha–1 due to a reduced ability to utilize natural rainfall. Average farm irrigation efficiencies calculated from actual pumping records were found to be low by world standards for the 3-year period 1975/76 to 1977/78. It was concluded that if increased production per unit of water became a high priority in the Namoi Valley, then irrigation efficiency for the three year period discussed could have been increased from 35 to 47%, a saving of 1.3 X 103 m3 ha–1 year–1.  相似文献   

10.
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   

11.
In Marlborough, New Zealand, olives are becoming an important crop alongside grapes. However, despite olives being drought resistant, they are generally planted on the poorer free-draining soils. Also, with the strong increase in cropping area, the demand for irrigation water has increased dramatically. In this research, we investigate the impact of short-term water stress on plant physiological processes, crop yield and oil quality in Marlborough, New Zealand. For that purpose, during the dry summer of 2000–2001, two trees were kept without irrigation for 64 days while two neighbouring trees were irrigated following standard practice. The trees were measured for transpiration (E), leaf and stem water potential (ΨL and ΨS), every other day, from dawn to dusk for three weeks from just before irrigation was started up again. All four trees were wired up for measuring stem sap flow (T) which was recorded hourly and a basic meteorological station provided weather data. Fruit and shoot development was measured weekly. It was found that under the short period of dry conditions with soil moisture (() dropping to <5%, olive trees kept functioning at a very low level with ΨL and ΨS reduced from −1 to <−4.0 MPa (T) reduced from 20 to 5 mm/h and (E) reduced from 1.5 to 1.0 mmol m−2 s−1. Within 10 days of restarting irrigation all these parameters were back to pre-drought levels. Both fruit and shoot growth came to a standstill within a week after drought was induced. During the first few days after re-watering, a high variability in ΨL was found between leaves from the same trees. This variability disappeared after six days. Shoot growth did not recover after re-watering but fruit growth rate, became the same as for continuously irrigated trees within days, but fruit size did not manage to recover before harvest. Yield from the dry trees was low because berry and pit weight were reduced by almost 50% at harvest, had a lower oil and percentage and were lower in phenolics. Stem sap flow was found to give a very good continuous measurement for the hydration status of the olive trees.  相似文献   

12.
In northeast Italy, a regimen of controlled drainage in winter and subirrigation in summer was tested as a strategy for continuous water table management with the benefits of optimizing water use and reducing unnecessary drainage and nitrogen losses from agricultural fields.To study the feasibility and performance of water table management, an experimental facility was set up in 1996 to reproduce a hypothetical 6-ha agricultural basin with different land drainage systems existing in the region. Four treatments were compared: open ditches with free drainage and no irrigation (O), open ditches with controlled drainage and subirrigation (O-CI), subsurface corrugated drains with free drainage and no irrigation (S), subsurface corrugated drains with controlled drainage and subirrigation (S-CI). As typically in the region free drainage ditches were spaced 30 m apart, and subsurface corrugated drains were spaced 8 m apart.Data were collected from 1997 to 2003 on water table depth, drained volume, nitrate-nitrogen concentration in the drainage water, and nitrate-nitrogen concentration in the groundwater at various depths up to 3 m.Subsurface corrugated drains with free drainage (S) gave the highest measured drainage volume of the four regimes, discharging, on average, more than 50% of annual rainfall, the second-highest concentration of nitrate-nitrogen in the drainage water, and the highest nitrate-nitrogen losses at 236 k ha−1.Open ditches with free drainage (O) showed 18% drainage return of rainfall, relatively low concentration of nitrate-nitrogen in the drainage water, the highest nitrate-nitrogen concentration in the shallow groundwater, and 51 kg ha−1 nitrate-nitrogen losses.Both treatments with controlled drainage and subirrigation (O-CI and S-CI) showed annual rainfall drainage of approximately 10%. O-CI showed the lowest nitrate-nitrogen concentration in the drainage water, and the lowest nitrogen losses (15 kg ha−1). S-CI showed the highest nitrate-nitrogen concentration in the drainage water, and 70 kg ha−1 nitrate-nitrogen losses. Reduced drained volumes resulted from the combined effects of reduced peak flow and reduced number of days with drainage.A linear relationship between daily cumulative nitrate-nitrogen losses and daily cumulative drainage volumes was found, with slopes of 0.16, 0.12, 0.07, and 0.04 kg ha−1 of nitrate-nitrogen lost per mm of drained water in S-CI, S, O, and O-CI respectively.These data suggest that controlled drainage and subirrigation can be applied at farm scale in northeast Italy, with advantages for water conservation.  相似文献   

13.
The YinNan Irrigation District in NingXia, China diverts each year about 1.6 × 109 m3 water from the Yellow River for irrigation use. More than half of that water is discharged back to the downstream channel or some low-lying depressions as a result of agricultural drainage. Several studies have indicated that the District is excessively drained, partially caused by the over-dimensioning of the existing drainage system, and proposed to improve the situation by controlled drainage practice. We subsequently carried out a field experiment of controlled drainage in the rice growing area of the District in 2004–2005. Field observations showed that reduction of the drainage depth of field ditches from 1 to 0.4 m resulted in a drainage flow reduction of 50–60%. Drainage water salinity increased only slightly but was still below the salt tolerance level of rice. Measurements of nitrogen concentrations showed no clear trend of changes as the result of irregular fertilization practice in the experimental site.  相似文献   

14.
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   

15.
A great challenge for the agricultural sector is to produce more food from less water, particularly in arid and semi-arid regions which suffer from water scarcity. A study was conducted to evaluate the effect of three irrigation methods, using effluent versus fresh water, on water savings, yields and irrigation water use efficiency (IWUE). The irrigation scheduling was based on soil moisture and rooting depth monitoring. The experimental design was a split plot with three main treatments, namely subsurface drip (SSD), surface drip (SD) and furrow irrigation (FI) and two sub-treatments effluent and fresh water, which were applied with three replications. The experiment was conducted at the Marvdasht city (Southern Iran) wastewater treatment plant during 2005 and 2006. The experimental results indicated that the average water applied in the irrigation treatments with monitoring was much less than that using the conventional irrigation method (using furrows but based on a constant irrigation interval, without moisture monitoring). The maximum water saving was obtained using SSD with 5907 m3 ha−1 water applied, and the minimum water saving was obtained using FI with 6822 m3 ha−1. The predicted irrigation water requirements using the Penman-Monteith equation (considering 85% irrigation efficiency for the FI method) was 10,743 m3 ha−1. The pressure irrigation systems (SSD and SD) led to a greater yield compared to the surface method (FI). The highest yield (12.11 × 103 kg ha−1) was obtained with SSD and the lowest was obtained with the FI method (9.75 × 103 kg ha−1). The irrigation methods indicated a highly significant difference in irrigation water use efficiency. The maximum IWUE was obtained with the SSD (2.12 kg m−3) and the minimum was obtained with the FI method (1.43 kg m−3). Irrigation with effluent led to a greater IWUE compared to fresh water, but the difference was not statistically significant.  相似文献   

16.
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   

17.
Summary Irrigated cultivation of pecans (Carya illinoensis K.) has increased dramatically in the Southwestern USA, yet their tolerance to salinity remains largely unknown. The first part of this study was conducted to assess if stunted tree growth reported in clayey soils is related to salinity, and the second part was to evaluate changes in soil salinity and the performance of 11 year old Western trees irrigated with water of 1.1 dSm–1 and 4.3 dSm–1 for 4 years. The first study, conducted at a commercial orchard (49 ha) in the El Paso valley (TX), showed a highly significant correlation between tree trunk size and salinity of the saturation extract (ECe) with r=–0.89. Soil salinity above which trunk size decreased in excess of the standard error was 2.0 dSm–1 in ECe from 0–30 cm depth, and 3.0 dSm–1 in 0 to 60 cm depth with corresponding Na concentrations of 14 and 21 mmol l–1. Excessive accumulation of salts and Na was found only in silty clay and silty clay loam soils. The second study, conducted at a small experimental field (1 ha), indicated that irrigation with waters of 1.1 and 4.3 dSm–1 increased ECe of the top 60 cm profile from 1.5 to 2.2 and 4.2 dSm–1 and Na concentration in the saturation extract to 17 and 33 mmol l–1, respectively. The leaching fractions were estimated at 13 and 37% when irrigated with waters of 1.1 and 4.3 dSm–1, respectively. Tree growth progressively slowed in the saline plots irrigated with water of 4.3 dSm–1, and became minimal during the 4th year. The cumulative shoot length over the 4 year period was reduced by 24% and trunk diameter by 18% in the saline plots relative to nonsaline plots. Irrigation with the saline water also reduced nut yields by 32%, nut size by 15% and leaflet area by 26% on the 4 year average, indicating that pecans are only moderately tolerant to salinity. The concentration of Na, Cl and Zn in the middle leaflet pair did not differ significantly between the two treatments. Soil salinity provided a more reliable measure for assessing salinity hazard than leaf analysis. However, soil salinity was found to be highly spatially variable following a normal distribution within a soil type. This high variability needs to be recognized in soil sampling as well as managing irrigation.Contribution from Texas Agricultural Experimental Station, Texas A & M University System. This program was supported in part by a grant from the Binational Agricultural Research and Development (BARD) fund  相似文献   

18.
The DSSAT-CSM-CERES-Wheat V4.0 model was calibrated for yield and irrigation scheduling of wheat with 2004–2005 data and validated with 13 independent data sets from experiments conducted during 2002–2006 at the Punjab Agricultural University (PAU) farm, Ludhiana, and in a farmer's field near PAU at Phillaur, Punjab, India. Subsequently, the validated model was used to estimate long-term mean and variability of potential yield (Yp), drainage, runoff, evapo-transpiration (ET), crop water productivity (CWP), and irrigation water productivity (IWP) of wheat cv. PBW343 using 36 years (1970–1971 to 2005–2006) of historical weather data from Ludhiana. Seven sowing dates in fortnightly intervals, ranging from early October to early January, and three irrigation scheduling methods [soil water deficit (SWD)-based, growth stage-based, and ET-based] were evaluated. For the SWD-based scheduling, irrigation management depth was set to 75 cm with irrigation scheduled when SWD reached 50% to replace 100% of the deficit. For growth stage-based scheduling, irrigation was applied either only once at one of the key growth stages [crown root initiation (CRI), booting, flowering, and grain filling], twice (two stages in various combinations), thrice (three stages in various combinations), or four times (all four stages). For ET-driven irrigation, irrigations were scheduled based on cumulative net ETo (ETo-rain) since the previous irrigation, for a range of net ETo (25, 75, 125, 150, and 175 mm). Five main irrigation schedules (SWD-based, ET-driven with irrigation applied after accumulation of either 75 or 125 mm of ETo, i.e., ET75 or ET125, and growth stage-based with irrigation applied at CRI plus booting, or at CRI plus booting plus flowering stage) were chosen for detailed analysis of yield, water balance, and CWP and IWP. Nitrogen was non-limiting in all the simulations.Mean Yp across 36 years ranged from 5.2 t ha−1 (10 October sowing) to 6.4 t ha−1 (10 November sowing), with yield variations due to seasonal weather greater than variations across sowing dates. Yields under different irrigation scheduling, CWP and IWP were highest for 10 November sowing. Yields and CWP were higher for SWD and ET75-based irrigations on both soils, but IWP was higher for ET75-based irrigation on sandy loam and for ET150-based irrigation on loam. Simulation results suggest that yields, CWP, and IWP of PBW343 would be highest for sowing between late October and mid-November in the Indian Punjab. It is recommended that sowing be done within this planting period and that irrigation be applied based on the atmospheric demand and soil water status and not on the growth stage. Despite the potential limitations recognised with simulation results, we can conclude that DSSAT-CSM-CERES-Wheat V4.0 is a useful decision support system to help farmers to optimally schedule and manage irrigation in wheat grown in coarse-textured soils under declining groundwater table situations of the Indian Punjab. Further, the validated model and the simulation results can also be extrapolated to other areas with similar climatic and soil environments in Asia where crop, soil, weather, and management data are available.  相似文献   

19.
A relationship between crop yield and irrigation water salinity is developed. The relationship can be used as a production function to quantify the economic ramifications of practices which increase irrigation water salinity, such as disposal of surface and sub-surface saline drainage waters into the irrigation water supply system. Guidelines for the acceptable level of irrigation water salinity in a region can then be established. The model can also be used to determine crop suitability for an irrigation region, if irrigation water salinity is high. Where experimental work is required to determine crop yield response to irrigation water salinity, the model can be used as a first estimate of the response function. The most appropriate experimental treatments can then be allocated. The model adequately predicted crop response to water salinity, when compared with experimental data.Abbreviations A Crop threshold rootzone salinity in Equation of Maas and Hoffman (dS/m) - B Fractional yield reduction per unit rootzone salinity increase (dS/m)–1 - Ci Average salinity of applied water (dS/m) - Cr Average salinity of rainfall (dS/m) - Cs Linearly averaged soil solution salinity in the rootzone (dS/m) - Cse Linearly averaged soil saturation extract salinity in the rootzone (dS/m) - Cw Average salinity of irrigation supply water (dS/m) - Cz Soil solution salinity at the base of the crop rootzone (dS/m) - C Mean root water uptake weighted soil salinity in equation of Bernstein and François (1973) (dS/m) - Ep Depth of class A pan evaporation during the growing season (m) - ETa Actual crop evapotranspiration during the growing season (m) - ETm Maximum crop evapotranspiration during the growing season (m) - I The total depth of water applied during the growing season (including irrigation water and rainfall) (m) - K Empirical coefficient in leaching equation of Rhoades (1974) - Kc Crop coefficient for equation of Doorenbos and Pruit (1977) to estimate crop water use - Ky Yield response factor in equation of Doorenbos and Kassam (1974) - LF The leaching fraction - Ro Depth of rainfall runoff during the growing season (m) - R Depth of rainfall during the growing season (m) - W Depth of irrigation water applied during the growing season (m) - Y Relative crop yield - Ya Actual crop yield (kg) - Ym Maximum crop yield (kg) - /z Dimensionless depth for equation of Raats (1974), and empirical coefficient for the leaching equation of Hoffman and van Genutchen (1983)  相似文献   

20.
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   

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