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.     

Assessment of the effect of tie-ridging on smallholder maize yields in Malawi

Tie-ridging is being promoted in Malawi as an on-field rainwater harvesting technique to ensure a maize (Zea mais L.) crop during a dry or drought year. Resource-poor smallholder farmers are likely to take up tie-ridging if it increases and not decreases maize yield in most years. A numerical study was conducted to calculate the expected maize yield gain due to tie-ridging taking into account the probability of occurrence of drought, dry, normal and wet years (climatic uncertainty). Mean yields due to tie-ridging in drought, dry, normal and wet years at different N levels were derived from observed smallholder maize yield data using a linear nitrogen response model and field-observed retained rainwater amounts in tie-ridged fields. Simulation results indicate that tie-ridging will result in hybrid maize yield gain in a drought year (1050 kg ha⁻¹) and dry year (560 kg ha⁻¹). There will be a hybrid maize yield loss in a normal year (350 kg ha⁻¹) and wet year (700 kg ha⁻¹). For local maize, there will be a yield gain in a drought year (500 kg ha⁻¹), dry year (220 kg ha⁻¹) and normal year (120 kg ha⁻¹). There will be a slight yield loss in a wet year (60 kg ha⁻¹). Considering observed probability of the occurrence of drought, dry, normal and wet years in Malawi, the study reveals that there will be no hybrid maize yield gain in any coming year with tie-ridging. For local maize, the expected yield gain in any coming year was positive (133.3 kg ha⁻¹) but this gain is less than the minimum gain required considering the opportunity cost of labour (142.5 kg ha⁻¹). Thus under the smallholder conditions and climate of Malawi, the expected yield gain in any coming year due to tie-ridging is likely to be minimal and uneconomic.     

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.     

Water and nitrate movement in drip-irrigated onion under fertigation and irrigation treatments

Frequent fertigation of crops is often advocated in the technical and popular literature, but there is limited evidence of the benefits of high-frequency fertigation. Field experiments were conducted on an Indo-American Hybrid var., Creole Red, of onion crop during three winter seasons of 1999–2000 through 2001–2002 in coarse-textured soil of Delhi under the semi-arid region of India. Three irrigation levels of 60, 80 and 100% of the crop evapotranspiration (ET) and four fertigation frequencies of daily, alternate day, weekly and monthly comprised the fertigation treatment. Analysis of soil samples indicated considerable influence of fertigation frequency on NO₃-N distribution in soil profile. NO₃-N in lower soil profiles (30.0–60.0 cm soil depth) was marginally affected in daily, alternate day and weekly fertigation. However, fluctuations of NO₃-N content in 0.0–15.0, 15.0–30.0, 30.0–45.0 and 45.0–60.0 cm soil depth was more in monthly fertigation frequency. The level of soil NO₃-N after the crop season shows that more NO₃-N leached through the soil profile in monthly fertigation frequency. Amounts of irrigation water applied in three irrigation treatments proved to be too small to cause significant differences in the content of NO₃-N leached beyond rooting depth of onion. Yield of onion was not significantly affected in daily, alternate day and weekly fertigation, though there was a trend of lower yields with monthly fertigation. The highest yield was recorded in daily fertigation (28.74 t ha⁻¹) followed by alternate day fertigation (28.4 t ha⁻¹). Lowest yield was recorded in monthly fertigation frequency (21.4 t ha⁻¹). Application of 56.4 cm irrigation water and 3.4 kg ha⁻¹ urea per fertigation (daily) resulted in highest yield of onion with less leaching of NO₃-N.     

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

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

Risk analysis and economic viability of water harvesting for supplemental irrigation in semi-arid Burkina Faso and Kenya

Food insecurity affects a large portion of the population in sub-Saharan Africa (SSA). To meet future food requirements current rainfed farming systems need to upgrade yield output. One way is to improve water and fertiliser management in crop production. But adaptation among farmers will depend on perceived risk reduction of harvest failure as well as economic benefit for the household. Here, we present risk analysis and economical benefit estimates of a water harvesting (WH) system for supplemental irrigation (SI). Focus of the analysis is on reducing investment risk to improve self-sufficiency in staple food production. The analysis is based on data from two on-farm experimental sites with SI for cereals in currently practised smallholder farming system in semi-arid Burkina Faso and Kenya, respectively. The WH system enables for both SI of staple crop (sorghum and maize) and a fully irrigated off-season cash crop (tomatoes). Different investment scenarios are presented in a matrix of four reservoir sealants combined with three labour opportunity costs. It is shown that the WH system is labour intensive but risk-reducing investment at the two locations. The current cultivation practices do not attain food self-sufficiency in farm households. WH with SI resulted in a net profit of 151–626 USD year⁻¹ ha⁻¹ for the Burkina case and 109–477 USD year⁻¹ ha⁻¹ for the Kenya case depending on labour opportunity cost, compared to −83 to 15 USD year⁻¹ ha⁻¹ for the Burkina case and 40–130 USD year⁻¹ ha⁻¹ for the Kenyan case for current farming practices. Opportunity cost represents 0–66% of the investment cost in an SI system depending on type of sealant. The most economical strategy under local labour conditions was obtained using thin plastic sheeting as reservoir sealant. This resulted in a net profit of 390 and 73 USD year⁻¹ ha⁻¹ for the Burkina Faso and Kenyan respective site after household consumption was deducted. The analysis suggests a strong mutual dependence between investment in WH for SI and input of fertiliser. The WH system is only economically viable if combined with improved soil fertility management, but the investment in fertiliser inputs may only be viable in the long term when combined with SI.     

Modelling the effect of groundwater depth on yield-increasing interventions in rainfed lowland rice in Central Java,Indonesia

Because of drought and nutrient stress, the yields of rainfed lowland rice in Central Java, Indonesia, are generally low and unstable. Variation in groundwater depth can contribute to experimental variability in results of yield-increasing interventions. To test this hypothesis, we used the crop growth simulation model ORYZA2000 to explore the impacts of groundwater depth on the effect of sowing date, tillage, fertiliser-N application and supplementary irrigation on the yield of lowland rice at Jakenan, Central Java, Indonesia. ORYZA2000 was first parameterized and evaluated using data from eight seasons of field experiments between 1995 and 2000. The model adequately simulated the soil water balance, crop growth and grain yield. With shallow to medium groundwater depth (less than 0.5 m deep), rainfed rice yields are close to potential yields with timely sowing in the wet season. With groundwater tables fluctuating mostly between 0.5 and 1.5 m, rainfed yields are 0.5–1 Mg ha⁻¹ lower than potential yields with timely sowing. The decrease in yield with late sowing sets in earlier and proceeds faster with deeper groundwater depths. Deep tillage and supplementary irrigation increase yield more with deep groundwater tables than with shallow groundwater tables, but N fertilisation increases yield more with shallow than with deep groundwater tables. Groundwater depth should be taken into account in the selection of yield-increasing interventions.     

Role of straw mulching in non-continuously flooded rice cultivation

Rice (Oryza sativa L.) cultivation under non-flooded (NF) condition is a new alternative to the conventional flooded (CF) rice cultivation system in the regions where rainfall and fresh water resources are limited. Non-flooded rice cultivation may mediate rice growth performance and mulching may be good practice to reduce evapotranspiration and increase water use efficiency (WUE). The research objectives of this study were to investigate the effects of non-flooded cultivation with straw mulching on the rice agronomic traits and water use efficiency of the second rice cropping season (late rice). The treatments were conventional flooded rice cultivation, non-flooded rice cultivations without (NF-ZM) and with rice straw mulching (NF-SM). Irrigation water was 19950 m³ ha⁻¹ in 2003 and 15,850 m³ ha⁻¹ in 2004 in the CF treatments and 7200 m³ ha⁻¹ in 2003 and 5045 m³ ha⁻¹ in 2004 in the non-flooded rice fields (NF-ZM and NF-SM treatments).The field measurements showed that water seepage was 13,442 m³ ha⁻¹ in the CF treatment, 5510 m³ ha⁻¹ in the NF-ZM treatment and 5424 m³ ha⁻¹ in the NF-SM treatment. Rice straw mulching decreased evapotranspiration by 33% and 63% (in 2003), 36.5% and 57.1% (in 2004) to the NF-ZM treatment and CF treatment, respectively. Compared with the NF-ZM treatment, mulch application significantly increased the leaf area per plant, main root length, tap root length and root dry weight per plant of crop. The yield of the NF-SM treatment (2003: 6489 kg/hm²; 2004: 8574.8 kg/hm²) was similar with the value of the CF treatment (2003: 6811.5; 2004: 8630.5 kg/hm²), and much higher than the NF-ZM treatment (2003: 4716; 2004: 6394.8 kg/hm²). The order of irrigation water use efficiency (IWUE) and water use efficiency were as follows: NF-SM > NF-ZM > CF.     

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.     

Performance of sugarcane genotypes grown under sodic soil and water conditions

An experiment was conducted to evaluate the effect of residual sodium carbonates (RSC) of irrigation water on the growth and yield of sugarcane grown on sierozem light textured alkaline soil with sodic ground water and to study the performance of some promising sugarcane genotypes under these conditions. Treatments consisted of five levels of irrigations water viz RSC 2.8, 6.5, 12 me l⁻¹ and RSC 6.5 and 12.0 me l⁻¹ fully amended with gypsum. Plant and ratoon crops of eight genotypes of sugarcane were harvested. Cane yield and yield attributing characters like cane height, number of internodes per cane and number of millable canes were recorded. Juice quality viz percent juice extraction, percent sucrose, and commercial cane sugar (CCS%) in juice were determined at the harvest of crop. For both plant and ratoon crops, the average cane yield of all the genotypes of sugarcane and cane yield attributing characters decreased significantly with the increase in RSC of irrigation water to 6.5 and 12.0 me l⁻¹ (35% and 51% decline in the average cane yield for plant crop). For ratoon crop, the corresponding decrease in the average cane yield was less than the plant crop (only 14% and 21%). Amending RSC with gypsum increased the yield in all genotypes. The cane yield of various genotypes obtained under amended RSC with gypsum treatments were almost equal to the yield obtained under RSC 2.8 me l⁻¹ treatment (89% to 92% average cane yield for plant crop and 93% to 96% for ratoon crop). The effect of RSC of irrigation was variable for different genotypes (for example, for the plant crop of CoH 97, 65% and 76% and for CoH 108, 9% and 20% decline in the cane yield was observed with the application of high RSC irrigation water). As compared to plant crop, the ratoon crop of all genotypes recorded higher average cane yield and lesser decline in the cane yield with the application of high RSC irrigation water. Average juice extraction % decreased from 40.5% to 35.8%, and sugar yield decreased significantly (5.61 to 2.91 t ha⁻¹ for plant crop and 6.18 to 5.38 t ha⁻¹ for ratoon crop) with the increase in RSC of irrigation water, and amending RSC with gypsum increased the juice extraction % and sugar yield per unit area.     

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.     

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%.     

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.     

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.     

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.     

Forage production of cool season pasture grasses as related to irrigation

A significant portion of the irrigated acreage in the intermountain western U.S. is comprised of cool season grass pastures. Droughts, coupled with increasing demands for limited water supplies in the region, have decreased the water volumes available for irrigating these pastures and other crops. Consequently, relationship between crop yield and irrigation (water production functions) should be defined for various species and cultivars to help growers and water managers make appropriate selections based on water availability.During a 3-year study on the Colorado Plateau, a line-source irrigation system was used to evaluate the relationship between applied water and dry forage production of orchardgrass (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), meadow brome (Bromus riparius Rehmann), smooth brome (Bromus inermis Leyss.), two cultivars of intermediate wheatgrass (Elytrigia intermedium [Host] Nevski), crested wheatgrass (Agropyron cristatum L. Gaertn. X desertorum [Fisch. ex Link] J.A. Schultes) and perennial ryegrass (Lolium perenne L.). Irrigation treatments, including precipitation, ranged from 457 to 970 mm in 1996, 427 to 754 mm in 1997 and 490 to 998 mm in 1998. There was a positive linear relationship between yield and irrigation for all cultivars when averaged over all years but the relationships varied between cultivars and years. Orchardgrass, meadow brome and tall fescue produced more dry forage than the other grasses at the highest irrigation levels in all years. These grasses also produced the greatest rates of yield increase per unit of irrigation (average of 0.0129 Mg ha⁻¹ mm⁻¹) and exhibited greater yield stability from year to year than the other grasses at irrigation levels above 700 mm. The intermediate wheatgrasses produced more forage than the other grasses under limited irrigation (less than 600 mm) but the average production rate with irrigation (0.0066 Mg ha⁻¹ mm⁻¹) was only about half that of the aforementioned grasses. The average rate of forage produced per mm of irrigation was intermediate in the smooth brome (0.0096 Mg ha⁻¹) and lowest in the crested wheatgrass and perennial ryegrass (0.0048 and 0.0034 Mg ha⁻¹, respectively). These results suggest that orchardgrass and meadow brome be included in irrigated pastures receiving more than 700 mm of water annually while the intermediate wheatgrasses be selected for pastures receiving an annual water application of less than 700 mm.     

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.     

Groundwater quality in CR-V irrigation district (Bardenas I,Spain): Alternative scenarios to reduce off-site salt and nitrate contamination

Irrigated agriculture may negatively affect groundwater quality and increase off-site salt and nitrate contamination. Management alternatives aimed at reducing these potential problems were analysed in the 15498 ha CR-V Irrigation District (Spain) by monitoring 49 wells and modelling the hydrological regime in a representative well of the Miralbueno Aquifer. Groundwaters presented low to moderate electrical conductivity (EC) (mean = 0.89 dS/m) and high [NO₃⁻] (mean = 94 mg/L). The groundwater depth (GWD) during the 2001 hydrological year responded to the annual cycles of precipitation and irrigation as well as to the secondary cycles derived from irrigation scheduling. GWD were consistently simulated by the groundwater BAS-A model. Model results indicate that an increase in irrigation efficiency and the pumping of groundwater for irrigation will decrease GWD and aquifer's discharge by 56–70%, depending on scenarios. These recommendations will save good-quality water in the reservoir, will be beneficially economical to farmers, and will minimize off-site salt and nitrogen contamination.     

Effect of water supply and salinity on pima cotton

A field study was conducted in northwestern Negev to determine the effect of the amount of water and its salinity level on the yield of Pima cotton (cv. S5). Irrigations were applied by means of a double line-source sprinkler system using two parallel lines, each supplied with water of a different salinity. The water salinity ranged from 2 to 7.5 dS m⁻¹ and the seasonal water application ranged from 30.0 to 68.0 cm. With water amounts of up to 50.0 cm (42% of Class A evaporation), an increase in water salinity caused a reduction in the seed cotton yield and the salinity threshold increased with an increasing amount of water. The maximum yield of seed cotton (about 5000 kg ha⁻¹) was obtained with a water application of 50 cm and a water salinity between 4 to 5 dS m⁻¹. With seasonal water applications exceeding 50 cm, an increase in salinity increased the yield. This is attributed to a depression of excessive vegetative growth in the presence of large amounts of water.     

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.