Spatial and temporal distributions of nitrogen and crop yield as affected by nonuniformity of sprinkler fertigation

Deep percolation and nitrate leaching are important considerations in the design of sprinkler systems. Field experiments were therefore conducted to investigate the influence of nonuniformity of sprinkler irrigation on deep percolation and spatial distributions of nitrogen and crop yield during the growing season of winter wheat at an experiment station in Beijing, China. Three experimental plots of a sandy clay loam soil in the 0–40 cm depth interval and a loamy clay soil below 40 cm were irrigated with a sprinkler irrigation system that had a seasonal averaged Christiansen irrigation uniformity coefficient (CU) varying from 72 to 84%. Except for the fertilizer applied before planting, fertilizer was applied with the sprinkler irrigation system. The corresponding seasonal averaged CU for fertigation varied from 71 to 85%. Daily observation of matrix water potentials in the root zone showed that little deep percolation occurred. Consequently, the effect of sprinkler uniformity on deep percolation was minor during the irrigation season for the soil tested. Intensive gravimetric soil core samplings were conducted several times during the irrigation season in a grid of 5 m × 5 m for each plot to determine the spatial and temporal variation of NH₄-N and NO₃-N contents. Soil NH₄-N and NO₃-N exhibited high spatial variability in depth and time during the irrigation season with CU values ranging from 23 to 97% and the coefficient of variation ranging from 0.04 to 1.06. A higher uniformity of sprinkler fertigation produced a more uniform distribution of NH₄-N, but the distribution of NO₃-N was not related to fertigation. Rather it was related to the spatial variability of NO₃-N before fertigation began. At harvest, the distribution of dry matter above ground, nitrogen uptake, and yield were measured and the results indicated that sprinkler fertigation uniformity had insignificant effects on the parameters mentioned above. Field experimental results obtained from this study suggest that sprinkler irrigation if properly managed can be used as an efficient and environment-friendly method of applying water and fertilizers.     

Trickle and sprinkler irrigation of potato (Solanum tuberosum L.) in the Middle Anatolian Region in Turkey

The potato (Solanum tuberosum L.) is widely planted in the Middle Anatolian Region, especially in the Nigde-Nevsehir district where 25% of the total potato growing area is located and produces 44% of the total yield. In recent years, the farmers in the Nigde-Nevsehir district have been applying high amounts of nitrogen (N) fertilizers (sometimes more than 900 kg N ha⁻¹) and frequent irrigation at high rates in order to get a much higher yield. This situation results in increased irrigation and fertilization costs as well as polluted ground water resources and soil. Thus, it is critical to know the water and nitrogen requirements of the crop, as well as how to improve irrigation efficiency. Field experiments were conducted in the Nigde-Nevsehir (arid) region on a Fluvents (Entisols) soil to determine water and nitrogen requirements of potato crops under sprinkler and trickle irrigation methods. Irrigation treatments were based on Class A pan evaporation and nitrogen levels were formed with different nitrogen concentrations.The highest yield, averaging 47,505 kg ha⁻¹, was measured in sprinkler-irrigated plots at the 60 g m⁻³ nitrogen concentration level in the irrigation treatment with limited irrigation (480 mm). Statistically higher tuber yields were obtained at the 45 and 60 g m⁻³ nitrogen concentration levels in irrigation treatments with full and limited irrigation. Maximum yields were obtained with about 17% less water in the sprinkler method as compared to the trickle method (not statistically significant). On the loam and sandy loam soils, tuber yields were reduced by deficit irrigation corresponding to 70% and 74% of evapotranspiration in sprinkler and trickle irrigations, respectively. Water use of the potato crop ranged from 490 to 760 mm for sprinkler-irrigated plots and 565–830 mm for trickle-irrigated treatments. The highest water use efficiency (WUE) levels of 7.37 and 4.79 kg m⁻³ were obtained in sprinkle and trickle irrigated plots, respectively. There were inverse effects of irrigation and nitrogen levels on the WUE of the potato crops. Significant linear relationships were found between tuber yield and water use for both irrigation methods. Yield response factors were calculated at 1.05 for sprinkler methods and 0.68 for trickle methods. There were statistically significant linear and polynomial relationships between tuber yield and nitrogen amounts used in trickle and sprinkler-irrigated treatments, respectively. In sprinkler-irrigated treatments, the maximum tuber yield was obtained with 199 kg N ha⁻¹. The tuber cumulative nitrogen use efficiency (NUE_cu) and incremental nitrogen use efficiency (NUE_in) were affected quite differently by water, nitrogen levels and years. NUE_cu varied from 16 to 472 g kg⁻¹ and NUE_in varied from 75 to 1035 g kg⁻¹ depending on the irrigation method. In both years, the NH₄-N concentrations were lower than NO₃-N, and thus the removed nitrogen and nitrogen losses were found to be 19–87 kg ha⁻¹ for sprinkler methods and 25–89 kg ha⁻¹ for trickle methods. Nitrogen losses in sprinkler methods reached 76%, which were higher than losses in trickle methods.     

Soil N and salinity leaching after the autumn irrigation and its impact on groundwater in Hetao Irrigation District,China

Soil water and salinity are crucial factors influencing crop production in arid regions. An autumn irrigation system employing the application of a large volume of water (2200–2600 m³ ha⁻¹) is being developed in the Hetao Irrigation District of China, since the 1980s with the goal to reduce salinity levels in the root zone and increase the water availability for the following spring crops. However, the autumn irrigation can cause significant quantities of NO₃⁻ to leach from the plant root zone into the groundwater. In this study, we investigated the changes in soil water content, NO₃–N and salinity within a 150 cm deep soil profile in four different types of farmlands: spring wheat (F_W), maize (F_M), spring wheat–maize inter-planting (F_W–M) and sunflower (F_S). Our results showed that (1) salt losses mainly occurred in the upper 60 cm of the soil and in the upper 40 cm for NO₃–N; (2) the highest losses of salt and NO₃–N could be observed in F_W, whereas the lowest losses were found in F_W–M.NO₃–N concentration, pH and electrical conductivity (EC) in the groundwater were also monitored before and after the autumn irrigation. We found that the autumn irrigation caused the groundwater concentration of NO₃–N to increase from 1.73 to 21.6 mg L⁻¹, thereby, exceeding the standards of the World Health Organization (WHO). Our results suggest that extensive development of inter-planting tillage might be a viable measure to reduce groundwater pollution, and that the application of optimized minimum amounts of water and nitrogen to meet realistic yield goals, as well as the timely application of N fertilizers and the use of slow release fertilizers can be viable measures to minimize nitrate leaching.     

Potential nitrate losses under different agricultural practices in the pampas region,Argentina

Fertilization is an important cause of groundwater contamination with nitrate in agricultural soils. The objectives of the present work were: (i) to quantify the nitrate leaching in two fertilized and irrigated soils of the Pampas Region, Argentina; (ii) to test the ability of the NLEAP model to predict residual and leached nitrate in those soils. The soils were a Typic Hapludoll and a Typic Argiudoll. The treatments were: natural grassland never ploughed or fertilized; maize with a short history of fertilization; maize with a long history of fertilization; irrigated maize with a long history of fertilization. Both sites were sampled after harvest in two consecutive years to a 3 m depth. Residual nitrate and potential losses below 150 cm were estimated by NLEAP model. The average amount of nitrate (NO₃-N), including values of all treatments, in the upper layer (0–1.5 m) was 128 kg NO₃-N ha⁻¹ in the first sampling date and was consistently lower in the second sampling date (38 kg NO₃-N ha⁻¹). In the deeper layer (1.5–3 m) these values were 80 and 28 kg NO₃-N ha⁻¹ for the first and second sampling date, respectively. Differences between the non-fertilized and the fertilized treatments were significantly smaller in the second sampling date. Obtained results suggest that the rainfall previous to the first sampling was not enough to displace nitrate below 3 m depth. The afterwards heavy rainfall leached nitrate previously accumulated in the soil. Complementary irrigation did not affect nitrate movements. Simulated residual and leached nitrate showed a high correlation with observed values. Nitrate leaching was more associated to rainfall regime and crop yields than to soil type. Simulated residual and leached nitrate showed a high correlation with measured values in both soils, which suggests that NLEAP was appropriate to predict soil nitrate leaching under the studied conditions.     

Comparison of sprinkler,trickle and furrow irrigation efficiencies for onion production

In the Mesilla Valley of southern New Mexico, furrow irrigation is the primary source of water for growing onions. As the demand for water increases, there will be increasing competition for this limited resource. Water management will become an essential practice used by farmers. Irrigation efficiency (IE) is an important factor into improving water management but so is economic return. Therefore, our objectives were to determine the irrigation efficiency, irrigation water use efficiency (IWUE) and water use efficiency (WUE), under sprinkler, furrow, and drip irrigated onions for different yield potential levels and to determine the IE associated with the amount of water application for a sprinkler and drip irrigation systems that had the highest economic return.Maximum IE (100%) and economic return were obtained with a sprinkler system at New Mexico State University’s Agriculture Science Center at Farmington, NM. This IE compared with the 54–80% obtained with the sprinkler irrigation used by the farmers. The IEs obtained for onion fields irrigated with subsurface drip irrigation methods ranged from 45 to 77%. The 45% represents the nonstressed treatments, in which an extra amount of irrigation above the evapotranspiration (Et) requirement was applied to keep the base of the onion plates wet. The irrigation water that was not used for Et went to deep drainage water. The return on the investment cost to install a drip system operated at a IE of 45 was 29%. Operating the drip system at a IE of 79% resulted in a yield similar to surface irrigated onions and consequently, it was not economical to install a drip system. The IEs at the furrow-irrigated onion fields ranged from 79 to 82%. However, the IEs at the furrow-irrigated onion fields were high because farmers have limited water resources. Consequently, they used the concept of deficit irrigation to irrigate their onion crops, resulting in lower yields. The maximum IWUE (0.084 t ha⁻¹ mm⁻¹ of water applied) was obtained using the sprinkler system, in which water applied to the field was limited to the amount needed to replace the onions’ Et requirements. The maximum IWUE values for onions using the subsurface drip was 0.059 and 0.046 t ha⁻¹ mm⁻¹ of water applied for furrow-irrigated onions. The lower IWUE values obtained under subsurface drip and furrow irrigation systems compared with sprinkler irrigation was due to excessive irrigation under subsurface drip and higher evaporation rates from fields using furrow irrigation. The maximum WUE for onions was 0.009 t ha⁻¹ mm⁻¹ of Et. In addition, WUE values are reduced by allowing the onions to suffer from water stress.     

Performance of temperate aerobic rice under different water regimes in North China

Since the late 1990s, aerobic rice varieties have been released to farmers in the North China Plain to grow rice as a supplementary-irrigated upland crop to cope with water scarcity. Little is known about their yield potential, water use, water productivity (WP), and flood tolerance. In 2001–2002, experiments with aerobic rice varieties HD502 and HD297 and lowland rice variety JD305 were conducted under aerobic and flooded conditions. Under aerobic conditions, five irrigation treatments were implemented. Under flooded conditions, JD305 yielded up to 8.8 t ha⁻¹, HD502 up to 6.8 t ha⁻¹, and HD297 up to 5.4 t ha⁻¹. Under aerobic conditions, the aerobic varieties yielded higher than the lowland variety. HD502 produced 3–3.5 t ha⁻¹ with 450–500 mm total water input and 5.3–5.7 t ha⁻¹ with 650 mm water input and more. HD297 produced 3–3.5 t ha⁻¹ with 450–500 mm total water input and 4.7–5.3 t ha⁻¹ with 650 mm water input and more. The water productivity of aerobic rice under aerobic conditions was higher or on a par with that of the lowland variety under flooded conditions, reaching values of 0.6–0.8 g grain kg⁻¹ water. The relatively high yields of the aerobic varieties under aerobic soil conditions were obtained under “harsh” conditions for growing rice. The soil contained more than 80% sand, was permeable, and held water above field capacity for a few hours after irrigation only. The groundwater table was deeper than 20 m, the soil moisture content in the rootzone was mostly between 50 and 80% of saturation, and soil moisture tension went up to 90 kPa. We conclude that the aerobic rice varieties HD502 and HD297 are suitable for water-scarce environments, and can stand being periodically flooded.     

Spatial variability of solutes in a pecan orchard surface-irrigated with untreated effluents in the upper Rio Grande River basin

Untreated effluents are blended with water from the Rio Grande River and used for irrigation in the Juarez Valley of northern Mexico. Effluents are a source of nutrients, but may also be a source of heavy metal contamination. This study was conducted to characterize deposition patterns of selected metals, salts, and total nitrogen in a 6 ha pecan (Carya illinoenisis K.) orchard which had healthy-to-stunted trees with dieback. Orchard soil was collected along multiple transects to depths of 1.2 m, with spacing every 20 m. All solutes showed a magnitude variability in particular ions. Chromium, Ni, Pb, and Cd concentrations averaged <14 mg kg⁻¹. Soil Na, Ca, K, Mg, SO₄, Cl and NO₃–N averaged <100 mg kg⁻¹. Total N was <0.21%. Most solutes accumulated at the soil surface with the exception of Na and SO₄. Linear semi-variograms best described spatial metal deposition and surface clay content with a range of influence >189 m. Spherical semi-variograms best described spatial distribution of salts and total N, but accounted <50% of the variability. The solubility of solutes in moderately alkaline irrigation water and their specific behavior in calcareous soils likely affected deposition patterns. Estimated metal loads from irrigation over a 15-year period were <3 kg ha⁻¹, but about 187 Mg ha⁻¹ for total dissolved solids (salts). Pecan leaf tissue showed no signs of heavy metal accumulation. Suboptimum pecan growth was associated with salt accumulation in a clayey area with low permeability. Salts, in particular Na, rather than metals may be the most important inorganic contaminants for irrigated agriculture in this region. Salt loads in irrigation waters are expected to increase as agriculture increasingly relies on urban effluents too expensive to convert to potable water.     

Cotton yield and applied water relationships under drip irrigation

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

Water use and lint yield response of drip irrigated cotton to the length of irrigation season

A 2-year experiment was conducted at Tal Amara Research Station in the Bekaa Valley of Lebanon to determine water use and lint yield response to the length of irrigation season of drip irrigated cotton (Gossypium hirsutum L.). Crop evapotranspiration (ET_crop) and reference evapotranspiration (ET_rye-grass) were directly measured at weekly basis during the 2001 growing period using crop and rye-grass drainage lysimeters. Crop coefficients (K_c) in the different growth stages were calculated as ET_crop/ET_rye-grass. Then, the calculated K_c values were used in the 2002 growing period to estimate evapotranspiration of cotton using the FAO method by multiplying the calculated K_c values by ET_rye-grass measured in 2002. The length of irrigation season was determined by terminating irrigation permanently at first open boll (S1), at early boll loading (S2), and at mid boll loading (S3). The three treatments were compared to a well-watered control (C) throughout the growing period. Lint yield was defined as a function of components including plant height at harvest, number of bolls per plant, and percentage of opened bolls per plant.Lysimeter-measured crop evapotranspiration (ET_crop) totaled 642 mm in 2001 for a total growing period of 134 days, while when estimated with the FAO method in 2002 it averaged 669 mm for a total growing period of 141 days from sowing to mature bolls. Average K_c values varied from 0.58 at initial growth stages (sowing to squaring), to 1.10 at mid growth stages (first bloom to first open boll), and 0.83 at late growth stages (early boll loading to mature bolls).Results showed that cotton lint yields were reduced as irrigation amounts increased. Average across years, the S1 treatment produced the highest yield of 639 kg ha⁻¹ from total irrigations of 549 mm, compared to the S2 and S3 treatments, which yielded 577 and 547 kg ha⁻¹ from total irrigations of 633 and 692 mm, respectively, while the control resulted in 457 kg ha⁻¹ of lint yield from 738 mm of irrigation water. Water use efficiency (WUE) was found to be higher in S1 treatment and averaged 1.3 kg ha⁻¹ mm⁻¹, followed by S2 (1.1 kg ha⁻¹ mm⁻¹), and S3 (1.0 kg ha⁻¹ mm⁻¹), while in the control WUE was 0.80 kg ha⁻¹ mm⁻¹. Lint yield was negatively correlated with plant height and the number of bolls per plant and positively correlated with the percentage of opened bolls. This study suggests that terminating irrigation at first open boll stage has been found to provide the highest cotton yield with maximum WUE under the semi-arid conditions of the Bekaa Valley of Lebanon.     

Irrigation management and hydrosalinity balance in a semi-arid area of the middle Ebro river basin (Spain)

The analysis of irrigation and drainage management and their effects on the loading of salts is important for the control of on-site and off-site salinity effects of irrigated agriculture in semi-arid areas. We evaluated the irrigation management and performed the hydrosalinity balance in the D-XI hydrological basin of the Monegros II system (Aragón, Spain) by measuring or estimating the volume, salt concentration and salt mass in the water inputs (irrigation, precipitation and Canal seepage) and outputs (evapotranspiration and drainage) during the period June 1997–September 1998. This area is irrigated by solid-set sprinklers and center pivots, and corn and alfalfa account for 90% of the 470 ha irrigated land. The soils are low in salts (only 10% of the irrigated land is salt-affected), but shallow (<2 m) and impervious lutites high in salts (average EC_e=10.8 dS m⁻¹) and sodium (average SAR_e=20 (meq l⁻¹)^0.5) are present in about 30% of the study area.The global irrigation efficiency was high (Seasonal Irrigation Performance Index=92%), although the precipitation events were not sufficiently incorporated in the scheduling of irrigation and the low irrigation efficiencies (60%) obtained at the beginning of the irrigated season could be improved by minimising the large post-planting irrigation depths given to corn to promote its emergence. The salinity of the irrigation water was low (EC=0.36 dS m⁻¹), but the drainage waters were saline (EC=7.5 dS m⁻¹) and sodic (SAR=10.3 (meq l⁻¹)^0.5) (average values for the 1998 hydrological year) due to the dissolution and transport of the salts present in the lutites. The discharge salt loading was linearly correlated (P<0.001) with the volume of drainage. The slope of the daily mass of salts in the drainage waters versus the daily volume of drainage increased at a rate 25% higher in 1997 (7.6 kg m⁻³) than in 1998 (6.1 kg m⁻³) due to the higher precipitation in 1997 and the subsequent rising of the saline watertables in equilibrium with the saline lutites. Drainage volumes depended (P<0.001) on irrigation volumes and were very low (194 mm for the 1998 hydrological year), whereas the salt loading was moderate (13.5 Mg ha⁻¹ for the 1998 hydrological year) taking into account the vast amount of salts stored within the lutites. We concluded that the efficient irrigation and the low salinity of the irrigation water in the study area allowed for a reasonable control of the salt loading conveyed by the irrigation return flows without compromising the salinization of the soil’s root-zone.     

Soil–plant water status and yield of sweet corn (Zea mays L. cv. Saccharata) as influenced by drip irrigation and planting methods

A field experiment was conducted during summer season of 1998 at the Main Research Station, University of Agricultural Sciences, Hebbal, Bangalore. Experiment consisted of four irrigation levels and two methods of planting. Drip irrigation at 0.8 Epan with normal planting recorded significantly higher green cob (20.07 t ha⁻¹) and fodder yield (24.87 t ha⁻¹) compared to either drip at 0.6 Epan or weekly surface irrigation at 0.8 Epan, while drip at 0.4 Epan under paired planting (10.53 and 15.23 t ha⁻¹, respectively registered the lowest. Drip at 0.4 Epan with normal planting recorded higher WUE of green cob and fodder (48.21 and 61.22 kg ha mm⁻¹) with total water requirement of 330.46 mm. With increase in water use (drip at 0.6 Epan, drip/surface irrigation at 0.8 Epan) the water use efficiency decreased. Drip irrigation at 0.8 Epan resulted in higher leaf water potential (−4, −7, −8 bars) at 20, 40 and 60 DAS before irrigation. Consequently, the RWC in the leaf was 81.10% and the available soil moisture ranged from 55.62 to 61.91%.     

Environmental impact and economic benefits of site-specific nutrient management (SSNM) in irrigated rice systems

Site-specific nutrient management (SSNM) provides a field-specific approach for dynamically applying nutrients to rice as and when needed. This approach advocates optimal use of indigenous nutrients originating from soil, plant residues, manures, and irrigation water. Fertilizers are then applied in a timely fashion to overcome the deficit in nutrients between the total demand by rice to achieve a yield target and the supply from indigenous sources. We estimated environmental impact of SSNM and evaluated economic benefits in farmers’ fields in southern India, the Philippines, and southern Vietnam for two cropping seasons in 2002–2003. On-farm research comparing SSNM and the farmers’ fertilizer practice showed increased yield with SSNM for the three locations, even with reduced fertilizer N rates in some cases. SSNM increased partial factor productivity (kg grain kg⁻¹ fertilizer N) when fertilizer N use efficiency with the farmers’ fertilizer practice was relatively low such as at locations in Vietnam and the Philippines. Use of on-farm data with the DNDC model revealed lower percentage of total N losses from applied fertilizers with SSNM during an annual cycle of cropping and fallows. At the location in India, SSNM showed the potential of obtaining higher yields with increased fertilizer N use while maintaining low N₂O emissions. SSNM in the Philippines and Vietnam showed greater yields with less fertilizer N through improved fertilizer use efficiency, which could reduce N₂O emissions and global warming. Use of SSNM never resulted in increased emissions of N₂O per unit of grain yield, and in environments where higher yield could be obtained with less fertilizer N, the use of SSNM could result in reduced N₂O emissions per unit of grain yield. For the economic analysis, data were generated through focus group discussions (FGD) with farmers practicing SSNM and with other farmers not practicing SSNM. Based on FGD, the seasonal increase in yield of farmers solely due to use of SSNM averaged 0.2 Mg ha⁻¹ in southern Vietnam, 0.3 Mg ha⁻¹ in the Philippines, and 0.8 Mg ha⁻¹ in southern India. Farmers practicing SSNM at the study site in India used less pesticide. The added net annual benefit due to use of SSNM was 34 US$ ha⁻¹ year⁻¹ in Vietnam, 106 US$ ha⁻¹ year⁻¹ in the Philippines, and 168 US$ ha⁻¹ year⁻¹ in India. The increased benefit with SSNM was attributed to increased yield rather than reduced costs of inputs.     

Dry-period irrigation and fertilizer application affect water use and yield of spring wheat in semi-arid regions

Based on a field study on the semi-arid Loess Plateau of China, the strategies of limited irrigation in farmland in dry-period of normal-precipitation years are studied, and the effects on water use and grain yield of spring wheat of dry-period irrigation and fertilizer application when sowing are examined. The study includes four treatments: (1) with 90 mm dry-period irrigation but without fertilizer application (W); (2) with fertilizer application but without dry-period irrigation (F); (3) with 90 mm dry-period irrigation plus fertilizer application (WF); (4) without dry-period irrigation and fertilizer application (CK). The results indicate that dry-period irrigation resulted in larger and deeper root systems and larger leaf area index (LAI) compared with the non-irrigated treatments. The root/shoot ratio (R/S) in the irrigated treatments was significantly higher than in the non-irrigated treatments. The grain yields in F, W and WF are 1509, 2712 and 3291 kg ha⁻¹, respectively, which are 13.7, 104.3 and 147.9% higher than that (1328 kg ha⁻¹) of CK, and at the same time the grain yields in W and WF are also significantly higher than in F. Water use efficiencies (WUE) in terms of grain yield are 5.70 and 6.91 kg ha⁻¹ mm⁻¹ in W and WF, respectively, being 65.7 and 101.1% higher than that (3.44 kg ha⁻¹ mm⁻¹) of CK. The highest WUE and grain yield consistently occurred in WF, suggesting that the combination of dry-period irrigation and fertilizer application has a beneficial effect on improving WUE and grain yield of spring wheat.     

Estimating potential nitrate leaching in nitrogen fertilized and irrigated tomato using the computer model NLEAP

Groundwater pollution caused by leaching of NO₃-N from agricultural systems has caused public concern for decades. To preserve the groundwater and reduce economic losses for the farmers, a rapid and accurate estimation of NO₃-N moving below the root zone is crucial. In this study, the value of the computer program NLEAP (Nitrate Leaching and Economic Analysis Package) to simulate nitrate leaching was evaluated using data from an experiment conducted with 12 lysimeters (1.25 m i.d. and 2 m deep) in 1996 and 1997. Three tomato (H2274 variety) seedlings were planted in each lysimeter and nitrogen rates of 0, 80, 160, and 240 kg N ha⁻¹, as ammonium nitrate and ammonium sulphate, were applied to the lysimeters under a fixed irrigation program. Effluent was collected from the outlets of the lysimeters and analyzed for NO₃. The model adequately simulated nitrogen leaching for each year (R²=0.93 and P<0.03 for 1996, and R²=0.87 and P<0.06 for 1997). The high coefficients of determination, between observed and simulated values, revealed that the model can be successfully used to estimate the amount of the NO₃ leaching under the experimental conditions. The results also showed that the NO₃ available for leaching (NAL) values were important background information for determining an optimum N rate for groundwater quality and maximum gain, and NO₃ available for leaching (NAL), amount of NO₃ leached (NL), movement risk index (MRI), and annual leaching risk potential (ALRP) parameters should be considered together to estimate the nitrogen pollution risk.     

The role of supplemental irrigation and nitrogen in producing bread wheat in the highlands of Iran

The West Asia and North Africa (WANA) region, with a Mediterranean climate type, has an increasing deficit in cereal production, especially bread wheat. Rainfed cropping in the highlands of this region coincides with the severely cold winter with mostly, snow from November to April. Cereal yields, are low and variable mainly as a result of inadequate and erratic seasonal rainfall and associated management factors, such as late sowing (or late crop emergence). In an area where water is limited, small amounts of supplemental irrigation (SI) water can make up for the deficits in seasonal rain and produce satisfactory and sustainable yields. This field study (1999–2002) on a deep clay silty soil in north west of Iran was conducted with four SI levels (rainfed, 1/3, 2/3 and full irrigation requirements) combined with different N rates (0, 30, 60, 90 and 120 kg ha⁻¹) with one wheat variety (Sabalan). Yields of rainfed wheat varied with seasonal rainfall and its distribution. A delay in the crop emergence from October (SI treatment) to November (rainfed) consistently reduced yields. With irrigation, crop responses to nitrogen were generally significant up to 60 kg N ha⁻¹. An addition of only limited irrigation (1/3 of full irrigation) significantly increased yields and maximized water use efficiency (WUE). Use efficiency for water and N was greatly increased by SI. Under deficit irrigation, maximum WUE would be achieved when 60 kg N ha⁻¹ is combined with 1/3 of full SI. Early crop germination is essential to ensure adequate crop stand before the winter frost and to achieve high yield. Early emergence can be achieved by applying a small amount (40–50 mm) of SI after sowing. Thus, when limited SI is combined with appropriate management, wheat production can be substantially and consistently increased in this highland semi-arid zone.     

The effects of different irrigation regimes on cucumber (Cucumbis sativus L.) yield and yield characteristics under open field conditions

A study was conducted to determine the effects of different drip irrigation regimes on yield and yield components of cucumber (Cucumbis sativus L.) and to determine a threshold value for crop water stress index (CWSI) based on irrigation programming. Four different irrigation treatments as 50 (T-50), 75 (T-75), 100 (T-100) and 125% (T-125) of irrigation water applied/cumulative pan evaporation (IW/CPE) ratio with 3-day-period were studied.Seasonal crop evapotranspiration (ET_c) values were 633, 740, 815 and 903 mm in the 1st year and were 679, 777, 875 and 990 mm in the 2nd year for T-50, T-75, T-100 and T-125, respectively. Seasonal irrigation water amounts were 542, 677, 813 and 949 mm in 2002 and 576, 725, 875 and 1025 mm in 2003, respectively. Maximum marketable fruit yield was from T-100 treatment with 76.65 t ha⁻¹ in 2002 and 68.13 t ha⁻¹ in 2003. Fruit yield was reduced significantly, as irrigation rate was decreased. The water use efficiency (WUE) ranged from 7.37 to 9.40 kg m⁻³ and 6.32 to 7.79 kg m⁻³ in 2002 and 2003, respectively, while irrigation water use efficiencies (IWUE) were between 7.02 and 9.93 kg m⁻³ in 2002 and between 6.11 and 8.82 kg m⁻³ in 2003.When the irrigation rate was decreased, crop transpiration rate decreased as well resulting in increased crop canopy temperatures and CWSI values and resulted in reduced yield. The results indicated that a seasonal mean CWSI value of 0.20 would result in decreased yield. Therefore, a CWSI = 0.20 could be taken as a threshold value to start irrigation for cucumber grown in open field under semi-arid conditions.Results of this study demonstrate that 1.00 IW/CPE water applications by a drip system in a 3-day irrigation frequency would be optimal for growth in semiarid regions.     

Latent heat flux over a furrow-irrigated tomato crop using Penman–Monteith equation with a variable surface canopy resistance

The Penman–Monteith (P–M) model with a variable surface canopy resistance (r_c) was evaluated to estimate latent heat flux (LE) or crop evapotranspiration (ET) over a furrow-irrigated tomato crop under different soil water status and atmospheric conditions. The hourly values of r_c were computed as a function of environmental variables (air temperature, vapor pressure deficit, net radiation, and soil heat flux) and a normalized soil water factor (F), which varies between 0 (wilting point, θ_WP) and 1 (field capacity, θ_FC). The Food and Agricultural Organization (FAO-56) method was also evaluated to calculate daily ET based on the reference evapotranspiration, crop coefficient and water stress coefficient. The performance of the P–M model and FAO-56 method were evaluated using LE values obtained from the Bowen ratio system. On a 20 min time interval, the P–M model estimated daytime variation of LE with a standard error of the estimate (SEE) of 46 Wm⁻² and an absolute relative error (ARE) of 3.6%. Thus, daily performance of the P–M model was good under soil water content ranging from 118 to 83 mm (θ_FC and θ_WP being 125 and 69 mm, respectively) and LAI ranging from 1.3 to 3.0. For this validation period, the calculated values of r_c and F ranged between 20 and 114 s m⁻¹ and between 0.87 and 0.25, respectively. In this case, the P–M model was able to predict daily ET with a SEE of 0.44 mm h⁻¹ (1.1 MJ m⁻² d⁻¹) and an ARE of 3.9%. Furthermore, the FAO-PM model computed daily ET with SEE and ARE values of 1.1 mm h⁻¹ (2.8 MJ m⁻² d⁻¹) and 5.2%, respectively.     

Review of measured crop water productivity values for irrigated wheat,rice, cotton and maize

The great challenge of the agricultural sector is to produce more food from less water, which can be achieved by increasing Crop Water Productivity (CWP). Based on a review of 84 literature sources with results of experiments not older than 25 years, it was found that the ranges of CWP of wheat, rice, cotton and maize exceed in all cases those reported by FAO earlier. Globally measured average CWP values per unit water depletion are 1.09, 1.09, 0.65, 0.23 and 1.80 kg m⁻³ for wheat, rice, cotton_seed, cotton_lint and maize, respectively. The range of CWP is very large (wheat, 0.6–1.7 kg m⁻³; rice, 0.6–1.6 kg m⁻³; cotton_seed, 0.41–0.95 kg m⁻³; cotton_lint, 0.14–0.33 kg m⁻³ and maize, 1.1–2.7 kg m⁻³) and thus offers tremendous opportunities for maintaining or increasing agricultural production with 20–40% less water resources. The variability of CWP can be ascribed to: (i) climate; (ii) irrigation water management and (iii) soil (nutrient) management, among others. The vapour pressure deficit is inversely related to CWP. Vapour pressure deficit decreases with latitude, and thus favourable areas for water wise irrigated agriculture are located at the higher latitudes. The most outstanding conclusion is that CWP can be increased significantly if irrigation is reduced and crop water deficit is intendently induced.     

Yield response of greenhouse grown tomato to partial root drying and conventional deficit irrigation

Greenhouse grown tomato was used to test partial root drying (PRD), a newly developing irrigation technique to save irrigation water, in Spring- and Fall-planted fresh-market tomato (Lycopersicon esculentum L., cv. Fantastic) cultivar. The PRD practice simply requires wetting of one half of the rooting zone and leaving the other half dry, thereby utilizing reduced amount of irrigation water applied. The wetted and dry sides are interchanged in the subsequent irrigations. Six irrigation treatments were tested during the two-year work in 2000 and 2001: (1) FULL, control treatment where the full amount of irrigation water, which was measured using Class-A pan evaporation data, was applied to the roots on all sides of the plant; (2) 1PRD30, 30% deficit irrigation with PRD in which wetted and dry sides of the root zone were interchanged with every irrigation; (3) 1PRD50; (4) 2PRD50, 50% deficit irrigation with PRD in which wetted and dry sides of the root zone were interchanged every and every other irrigation, respectively; (5) DI30 and (6) DI50, 30 and 50% deficit irrigations, respectively. The defined deficit levels were all in comparison to FULL irrigation. During the first year study in 2000, only three treatments (FULL, 1PRD30 and 2PRD50) were tested. Five treatments with exception of 2PRD50 were included in 2001. The FULL irrigation treatment, in Spring-planted tomato having a 153 day growth period, yielded 110.9 t ha⁻¹. The resulting irrigation-water-use efficiency (IWUE) was 321.8 kg (ha mm)⁻¹. The 1PRD50 treatment gave 86.6 t ha⁻¹, which was not statistically different (P ≤ 0.05) from the FULL irrigation (the control) and had 56% higher IWUE. Although yield differences were not statistically significant in Fall-planted tomato, the highest fruit yield was again obtained under FULL irrigation treatment (205.2 t ha⁻¹) over a growth period of 259 days after transplanting. The PRD treatments had 7–10% additional yield over the deficit irrigation receiving the same amount of water. The PRD treatments gave 10–27% higher marketable tomato yield (>60 g per fruit), compared with the DI treatments. Abscisic acid (ABA) concentrations measured in fresh leaf tissue was the highest under PRD practice relative to FULL and DI treatments. The high ABA content of fresh-leaf tissue observed in the work supports the root signalling mechanism reported earlier in plants having undergone partial root drying cycles.     

Economics of drip irrigation of olives in Turkey

Agricultural growers need investment and cost guidelines for drip irrigation to evaluate the economics of getting crops into production as quickly as possible and to minimise economic losses from drought during the productive life of an olive orchard. The benefits of irrigation may include; better olive survival, earlier crop production, greater yields, efficient nutrient distribution, less plant stress, reduced yield variability and improved crop quality.This research was conducted to help olive growers make decisions regarding investments in drip irrigation systems. This analysis was aimed at the farm business level to provide an economic rationale for investing in drip irrigation systems.The net present value (NPV) criterion was used to determine the discounted break-even investment results from published responses to drip irrigation systems. Growers with typical drip irrigation systems can expect investments of US$ 2244 ha⁻¹ with 1.6 ha blocks of olives. Analysis of survey findings indicate that net present value was US$ 3464 ha⁻¹ after an initial investment of US$ 2244 ha⁻¹.