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.     

Responses of five almond cultivars to irrigation: Photosynthesis and leaf water potential

In the Trás-os-Montes region, almond orchards are usually planted in the dry soils on the upper valley of the Douro river and are typically cultivated under non-irrigated conditions, leading to low yields. This study aimed to compare the physiological responses of five almond varieties (Francoli, Ferragnès, Glorieta, Lauranne and Masbovera) growing under non-irrigated and irrigated conditions. In irrigated conditions, all cultivars had higher photosynthetic rates, with maximum rates in a range of 10–12 μmol CO₂ m⁻² s⁻¹. Study of daily photosynthesis (June–August) indicates that, irrigated plants showed maximal values at 11 h (32 °C), while in water stressed ones highest values were found at 9 h (28 °C). The irrigation induced an increase in photosynthesis of around 173% in Lauranne, 187% in Francoli, 204% in Glorieta, 266% in Masbovera and 331% in Ferragnès. In relation to values of water potential that allow half-rate of photosynthesis (ψ_w50), they were calculated as −2.95, −2.50, −3.10, −3.20 and −3.30 MPa for Ferragnès, Glorieta, Masbovera, Francoli and Lauranne, respectively.     

Sediment phosphorus dynamics for three tile fed drainage ditches in Northeast Indiana

Phosphorus (P) losses from agricultural lands degrade surface waters due to anthropogenic eutrophication. Previous studies focused on plot-to-field scale P loss and reductions from best management practices (BMP's), little information in intense agricultural catchments has been gathered on the dynamics influencing P beyond the edge of the field. This study was conducted to examine the phosphorus equilibrium between the water column and sediments in three tile fed drainage ditches in Northeast Indiana. Surface water and sediment samples were collected and analyzed for organic carbon (C), particle size and P from sites along three ditches with similar soils and land use at sites within each watershed draining approximately 300 and 1500 ha on each ditch. Organic C, silt and clay fractions of the bottom sediments decreased with increasing drainage area. Soluble P concentrations were low in Ditch A, but increased with increasing drainage area (0.02–0.05 mg P L⁻¹). Overall, the P concentrations were higher in the Ditches B and C (0.06–0.09 mg P L⁻¹). Exchangeable P, P partitioning index and equilibrium P concentrations (EPC_o) decreased with increasing drainage area by as much as 95, 93 and 100%, respectively, except in one catchment area with a confined animal feeding operation between sampling points, where ExP and EPC_o increased by 4 and 116%, respectively. Aluminum sulfate and calcium carbonate treatment of ditch sediments reduced exchangeable P and sediment EPC_o in this study. Results from this study indicated some watershed characteristics, as well as sediment physiochemical properties, affect ditch sediment and water P equilibrium and buffering capacity. Furthermore, this study demonstrated that managers could potentially use chemical treatment of the ditches to increase the temporary retention of P in ditches and maybe reducing sediment P availability.     

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.     

Shallow groundwater contribution to pistachio water use

Pistachio can be grown in the central desert of Islamic Republic (I.R.) of Iran with adverse conditions such as shallow saline groundwater tables. The contribution of water from shallow, saline groundwater to crop water use may be important in such conditions. The objectives of this study were to determine the contributions from shallow, saline groundwater to water use of pistachio seedlings, and how this contribution was affected by groundwater depth, salinitiy, and irrigation conditions. The results indicated that an increase in groundwater depth resulted in significant increase in root depth and significant decrease in seasonal evapotranspiration (ET), transpiration, and groundwater contribution to the plant water use. Non-saline shallow (30–120 cm depth) groundwater under irrigated and non-irrigated conditions contributed 72.4–89.7% and 90.7–100.0% of plant water use, respectively. However, these contributions were 57.2–74.8% and 79.3–100.0% for irrigated and non-irrigated conditions, respectively for saline shallow (30–120 cm depth) groundwater. The effect of groundwater depths (D, cm) on groundwater contributions (q, %) was found to be influenced by the salinity levels of the groundwater (EC, dS m⁻¹). The linear multiple regression equations were q = 97.5 − 1.24(EC) − 0.194(D) and q = 105.9 − 0.48(EC) − 0.154(D) for irrigated and non-irrigated conditions, respectively. The maximum reductions in relative plant dry weight of 80.3% and 44.8% were occurred under non-irrigated condition and saline groundwater depth of 30 cm and non-saline water depth of 60 cm, respectively. Root depth analysis indicated that vertical root growth caused the root to reach a moist layer near the groundwater. A very close to 1:1 relationship between relative reduction in top dry weight (1 − y/y_m) and relative reduction in transpiration (1 − T/T_m) was obtained.     

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.     

Response of safflower (Carthamus tinctorius L.) to saline soils and irrigation: I. Consumptive water use

Salt-tolerant crops can be grown with saline water from tile drains and shallow wells as a practical strategy to manage salts and sustain agricultural production in the San Joaquin Valley (SJV) of California. Safflower (Carthamus tinctorius L.) was grown in previously salinized plots that varied in average electrical conductivity (EC_e) from 1.8 to 7.2 dS m⁻¹ (0–2.7 m depth) and irrigated with either high quality (EC_i<1 dS m⁻¹) or saline (EC_i=6.7 dS m⁻¹) water. One response of safflower to increasing root zone salinity was decreased water use and root growth. Plants in less saline plots recovered more water on average (515 mm) and at a greater depth than in more salinized plots (435 mm). With greater effective salinity, drainage increased with equivalent water application rates. Seed yield was not correlated with consumptive water use over the range of 400–580 mm. Total biomass and plant height at harvest were proportional to water use over the same range. Safflower tolerated greater levels of salinity than previously reported. Low temperatures and higher than average relative humidity in spring likely moderated the water use of safflower grown under saline conditions.     

Response of two varieties of lentil to soil salanity

Two varieties of lentil were grown in tanks filled with clay, and were irrigated with waters containing three different levels of salinity. Salinity affected the germination and survival of the seedlings; the pre-dawn leaf-water potential and maximum osmotic adjustment; the development of leaf area, dry matter and number of flowers, and, finally, the yield.Lentil has a high water-use efficiency, about 2 kg m⁻³ under non-saline conditions, much higher than legumes such as broadbean and soybean. The crop, however, is much more salt sensitive and can only be grown on non-saline soils. At an EC_e of 2 dS/m, the limit between non-saline and slightly saline soils, the yield reduction is about 20% and at an EC_e of 3 dS/m it is 90–100%.The salt tolerance classification, made after a greenhouse experiment with nutritive solutions, was not confirmed by the experiments reported here.     

Irrigation with saline water in the reclaimed marsh soils of south-west Spain: impact on soil properties and cotton and sugar beet crops

The drained and irrigated marshes in south-west Spain are formed on soils of alluvial origin from the ancient Guadalquivir river estuary. The most important characteristics of these soils are the high clay content (about 70%), high salinity, and a shallow, extremely saline, water table. The reclaimed area near Lebrija, called Sector B-XII (about 15,000 ha), has been under cultivation since 1978. Some years, however, water supply for irrigation is limited due to drought periods. The objective of this work was to evaluate the effects of irrigation with high and moderately saline waters on soil properties and growth and yield of cotton and sugar beet crops. The experiments were carried out during 1997 and 1998 in a farm plot of 12.5 ha (250 m×500 m) in which a drainage system had been installed, consisting of cylindrical ceramic sections (0.3 m long) forming pipes 250 m long, buried at a depth of 1 m and spaced at intervals of 10 m. These drains discharge into a collecting channel perpendicular to the drains. Two subplots of 0.5 ha (20 m×250 m) each were selected. In 1997 cotton was growing in both subplots, and irrigation was applied by furrows. One subplot (A) was irrigated with fresh water (0.9 dS m⁻¹) during the whole season, while in the other subplot (B) one of the irrigations (at flowering stage) was with water of high salinity (22.7 dS m⁻¹). During 1998 both subplots were cropped with sugar beet. Subplot A was irrigated with fresh water (1.7 dS m⁻¹) during the whole season, while in subplot B two of the irrigations were with moderately saline water (5.9–7.0 dS m⁻¹). Several measurement sites were established in each subplot. Water content profile, tensiometric profile, water table level, drainage water flow, soil salinity, and crop development and yield were monitored. The results showed that after the irrigation with high saline water (subplot B) in 1997 (cotton), the soil salinity increased. This increase was more noticeable in the top layer (0–0.3 m depth). In contrast, for the same dates, the soil of subplot A showed no changes. After five irrigations with fresh water, the salinity of the soil in the subplot B reached values similar to those before the application of saline water. In 1998 (sugar beet) the application of moderately saline water in subplot B also increased soil salinity, but this increase was lower than in 1997. The irrigation with high saline water affected crop development. Cotton growth was reduced in comparison with that in the subplot irrigated only with fresh water. Despite this negative effect on crop development, the crop yield was the same as in the subplot A. Sugar beet development did not show differences between subplots, but yield was higher in subplot B than in subplot A.     

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.     

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.     

An ecological optimality approach for predicting deep drainage from tree belts of alley farms in water-limited environments

The clearing of natural vegetation for agriculture in southern Australia has increased deep drainage, led to increased groundwater recharge and, hence, the salinisation of land and streams. Alley farming systems, comprising alternate belts of trees and crops, have been proposed for reducing deep drainage but their effectiveness is unknown. This paper describes an application of ecological optimality theory to estimate the equivalent no drainage (ENOD) width B (m) for a tree belt. The relative drainage RD from an alley farm, compared to conventional agriculture is, therefore, 1 − B/W, where W is the centre spacing of the belts. We present a method for estimating B_LA from the leaf area per unit length of belt LLA (m² m⁻¹), divided by the leaf area index LAI (m² m⁻²) of nearby natural vegetation. Preliminary evaluation of B_LA showed good agreement with B_WB measured from water balance and B_DD measured from deep drainage. The estimation of B_LA for calculation of RD allows rapid estimates of the relative drainage reduction expected from alley farms in water-limited environments.     

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.     

Effect of water-saving irrigation on rice yield and water use in typical lowland conditions in Asia

With decreasing water availability for agriculture and increasing demand for rice, water use in rice production systems has to be reduced and water productivity increased. Alternately submerged–nonsubmerged (ASNS) systems save water compared with continuous submergence (CS). However, the reported effect on yield varies widely and detailed characterizations of the hydrological conditions of ASNS experiments are often lacking so that generalizations are difficult to make. We compared the effects of ASNS and CS on crop performance and water use, at different levels of N input, in field experiments in China and the Philippines, while recording in detail the hydrological dynamics during the experiment. The experiments were conducted in irrigated lowlands and followed ASNS practices as recommended to farmers in China. The sites had silty clay loam soils, shallow groundwater tables and percolation rates of 1–4.5 mm per day.Grain yields were 4.1–5.0 t ha⁻¹ with 0 kg N ha⁻¹ and 6.8–9.2 t ha⁻¹ with 180 kg N ha⁻¹. Biomass and yield did not significantly differ between ASNS and CS, but water productivity was significantly higher under ASNS than under CS in two out of three experiments. There was no significant water×N interaction on yield, biomass, and water productivity. Combined rainfall plus irrigation water inputs were 600–960 mm under CS, and 6–14% lower under ASNS. Irrigation water input was 15–18% lower under ASNS than under CS, but only significantly so in one experiment. Under ASNS, the soils had no ponded water for 40–60% of the total time of crop growth. During the nonsubmerged periods, ponded water depths or shallow groundwater tables never went deeper than −35 cm and remained most of the time within the rooted depth of the soil. Soil water potentials did not drop below −10 kPa. We argue that our results are typical for poorly-drained irrigated lowlands in Asia, and that ASNS can reduce water use up to 15% without affecting yield when the shallow groundwater stays within about 0–30 cm. A hydrological characterization and mapping of Asia’s rice area is needed to assess the extent and magnitude of potential water savings.     

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.     

Development and evaluation of integrated water and nitrogen model for maize

Maize (Zea mays L.) is an important food crop for irrigated regions in the world. Its growth and production may be estimated by different crop models in which various relationships between growth and environmental parameters are used. For simulation of maize growth and grain yield, a simulation model was developed (Maize Simulation Model, MSM). Dynamic flow of water, nitrogen (N) movement, and heat flow through the soil were simulated in unsteady state conditions by numerical analysis in soil depth of 0–1.8 m. Hourly potential evapotranspiration [ET_p(t)] for maize field was estimated directly by Penman–Monteith method. Hourly potential evaporation [E_p(t)] was estimated based on ET_p(t) and canopy shadow projection. Actual evaporation of soil surface was estimated based on its potential value, relative humidity of air, water pressure head and temperature at soil surface layer. Actual transpiration (T_a(t)) was estimated based on soil water content and root distribution at each soil layer. Hourly N uptake by plant was simulated by N mass flow and diffusion processes. Hourly top dry matter production (HDMA^j + 1, where j is number of hours after planting) was estimated by hourly corrected intercepted radiation (RSLT^j + 1) by plant leaves [determined from leaf area index (LAI^j + 1)] with air temperature, the maximum and minimum plant top N concentration and the amounts of nitrogen uptake. The value of LAI^j + 1 at each hour was estimated by the accumulated top dry matter production at previous hour using an empirical equation. Maize grain yield was estimated by a relationship between harvest index and seasonal plant top dry matter production. The model was calibrated using data obtained under field conditions by a line source sprinkler irrigation. When the values of water and nitrogen application were optimum, grain yield (moisture content of 15.5%) was 16.2 Mg ha⁻¹. Model was validated using two independent experimental data obtained from other experiments in the Badjgah (Fars province). The experimental results validated the proposed simulation model fairly well.     

Nitrogen loss through subsurface drainage effluent in coastal rice field from India

Experiments were conducted to estimate nitrogen loss through drainage effluent in subsurface drained farmers’ field at a coastal site near Machilipatnam, Andhra Pradesh, India. The concentration of three forms of nitrogen, namely, NH₄–N, NO₂–N and NO₃–N in the subsurface drainage effluent from 15, 35 and 55 m drain spacing areas were measured in 1999 and 2000. The area with 15 m spacing was already reclaimed during 1986–1998 by the subsurface drainage system. The soil salinity of the root zone was brought down from an initial high of 35 to 4 dS m⁻¹. The subsurface drainage system with 35 and 55 m drain spacing was laid in the adjoining area and commissioned in 1998. Earlier raising of any crop in the area with 35 and 55 m spacings was not possible due to very high salinity, sodicity and poor drainage conditions. The nitrate-nitrogen loss dominated in reclaimed land with 15 m spacing whereas ammonium-nitrogen loss dominated in the land that was highly saline and in the initial stage of reclamation by the subsurface drainage technology with 35 and 55 m drain spacing. The total nitrogen loss of 3.75 kg per ha per year in 15 m drain spacing area was minimum and 23.53 kg per ha per year in 35 m drain spacing area was maximum. The nitrate-nitrogen loss contributed the maximum of 82% and ammonium- and nitrite-nitrogen contributed 11 and 7%, respectively, in 15 m drain spacing area whereas the ammonium losses contributed 93 and 82% in 35 and 55 m drain spacing areas, respectively. The losses in the form of nitrite and nitrate remained negligible in 35 m drain spacing area, but the losses to the tune of 8 and 15% in the form of nitrite and nitrate, respectively, occurred in 55 m drain spacing area.     

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.     

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.     

The influence of crop canopy on evapotranspiration and crop coefficient of beans (Phaseolus vulgaris L.)

Experiments were conducted to investigate the effect of crop development on evapotranspiration and yield of beans (Phaseolus vulgaris L.) at the Instituto Agronômico (IAC), Campinas, State of São Paulo, Brazil, during the dry season of 1994. A completely randomized design was carried out with three population density treatments and four replications. The treatments were: (a) crop sown in evapotranspirometers at a density of 50 plants m⁻², and thereafter thinned to 25 plants m⁻², when the canopy achieved full ground cover; (b) crop sown with population densities of 14 and 28 plants m⁻² in an irrigated field. Crop growth was evaluated considering dry matter (DM), vegetative ground cover (GC%) and leaf area index (LAI). These parameters were successfully related to basal crop coefficient (k_cb) and crop coefficient (k_c), demonstrating the strong dependence of both coefficients on canopy development. A simulation study was carried out and showed that k_cb based on LAI would allow good estimates of water use for different plant density populations in the field.