Timing of limited irrigation and N-injection for grain sorghum

When subsurface irrigation sources are lacking in humid and subhumid regions, high yearly precipitation may allow for storage of surface water in farm ponds and lakes for irrigation. Irrigation at selected growth stages may avoid critical stress for crops with some drought tolerance, such as grain sorghum [Sorghum bicolor (L.) Moench]. Because grain sorghum is responsive to N, injecting fertilizer N through the irrigation system also may improve production. The objective of this study was to determine the effect of timing of limited-amount irrigation and N fertigation on grain sorghum yield; yield components; grain N content; and N uptake at the 9-leaf, boot, and soft dough stages. The experiment was conducted from 1984 to 1986 on a Parsons silt loam (fine, mixed, thermic, Mollic Albaqualf). The experiment was designed as a 6 × 2 factorial plus two reference treatments. Six timings for irrigation were targeted at the 9-leaf (9L), boot (B), soft dough (SD), 9L-B, 9L-SD, and B-SD growth stages. N application systems were either 112 kg N ha^–1 surface-banded preplant or 56 kg N ha^-1 preplant and 56 kg N ha^–1 injected through the irrigation at a rate of 28 kg N ha^–1 per 2.5 cm of irrigation. Two reference treatments included were one receiving N but no irrigation and one receiving neither N nor irrigation. In 1984, irrigation generally increased grain sorghum yield by nearly 1 Mg ha^–1. However, yield was not affected by selection of irrigation timing, N application method, or the interaction of the two factors. This was partly because early irrigations increased kernels/head, whereas later irrigations increased kernel weight. Above average rainfall during the growing season, especially just prior to the 9-leaf, boot, and soft dough growth stages, resulted in no irrigations in 1985. In 1986, yield was increased by early (9-leaf) irrigations as compared to soft dough irrigations. Early irrigations resulted in higher kernels/head; however, rainfall after the soft dough irrigation may have masked any treatment effect on kernel weight. As in 1984, N application method did not affect grain sorghum yields, even though yield was reduced to less than 3 Mg ha^–1 with no N nor irrigation. In both 1984 and 1986, N uptake at succeeding growth stages appeared to respond to irrigations made at previous growth stages. Injecting half of the fertilizer N through the irrigation system did not affect N uptake compared to applying all N preplant. The lack of response to fertigation may be related to the low leaching potential of the soil used in this study.Contribution No. 92-606-J, Kansas Agricultural Experiment Station     

Water use,growth and rubber yields of four guayule selections as related to irrigation regimes

Summary There has been renewed interest in cultivating guayule (Parthenium argentatum G.) for rubber production. Water use, growth and rubber yields of four guayule selections (593, 11.591, 11 646 and 4265 XF) were evaluated for two years in nonweighing field lysimeters at El Paso, TX. Four irrigation treatments were evaluated; these involved irrigation when about 40, 60 or 90% of available water was depleted, and the fourth treatment was irrigated at 60% depletion using saline water containing 3,300 mg of dissolved salts per liter. Water use for the two year period for these treatments amounted to 219, 147, 96 and 132 cm, respectively, plus biennial rainfall of 32 cm. Shrub and resin yields increased linearly with increasing irrigation, while rubber contents generally decreased with irrigation. Resultant rubber yields were highest under the lowest stress treatment, yielding about 840 kg/ha. Rubber yields with other treatments averaged 560 kg/ha with no significant yield differences among the tested selections. The salt treatment increased rubber contents of the shrubs, but caused reductions in shrub and rubber yields. Guayule plants survived well under low soil moisture, but water requirement to produce unit quantities of biomass was high (about 15 cm to produce one ton of dry shrub per ha). Guayule should not be regarded as a low water consuming crop if high yields per land area are to be achieved.Contribution from Texas Agricultural Experiment Station. This project was supported in part by a fund from USDA Latex Commission and Binational Agricultural Research and Development Fund (BARD). The authors are Associate Professor, and Technicians, respectively     

Effects of saline water irrigation on soil salinity,Pecan tree growth and nut production

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

Responses of grain sorghum to variable water supply under two irrigation frequencies

Summary Two experiments were conducted with Sorghum bicolor (L.) Moench Cv. Pioneer 846 in a deep loam soil in the 1977 season. Experiment I consisted of two line-source sprinkler plots, one irrigated at two-day intervals (HF) and the other every 10 to 14 days (NF). In comparable treatments of both regimes, the seasonal amount of water applied was the same. Since the subsoil was very dry at planting, the different amounts of water applied led to the development of a range of water stresses from none to severe. Experiment II was conducted in an adjacent area with a fully wetted soil profile. The treatments were irrigated every week (I) and nonirrigated (NI). Applied water was measured after each irrigation. Soil water content, leaf water potential, leaf-area index, ground cover and dry-matter accumulation were measured at frequent intervals, and yields were taken at the end of the growing season. Linear relations were found between both total dry-matter production and grain yield and seasonal evapotranspiration (ET) in both HF and NF regimes. With seasonal values of ET near the potential, grain yield and dry-matter production did not differ between irrigation frequencies. At low seasonal ET values, however, the NF regime gave greater yields of dry-matter and grain than did the HF regime.     

Wheat yield response to line source sprinkler irrigation and soil management practices on medium-textured shallow soils of arid environment

A field experiment was conducted for 3 years to evaluate the effect of deficit irrigation under different soil management practices on biomass production, grain yield, yield components and water productivity of spring wheat (Triticum estivum L.). Soil management practices consisted of tillage (conventional and deep tillage) and Farmyard manure (0 and 10 t ha^?1 FYM). Line source sprinkler laterals were used to generate one full- (ETm) and four deficit irrigation treatments that were 88, 75, 62 and 46 % of ETm, and designated as ETd₁, ETd₂, ETd₃, and ETd₄. Deep tillage significantly enhanced grain yield (14–18 %) and water productivity (1.27–1.34 kg m^?3) over conventional tillage. Similarly, application of FYM at 10 t ha^?1 significantly improved grain yield (10–13 %) and water productivity (1.25–1.31 kg m^?3) in comparison with no FYM. Grain yield response to irrigation varied significantly (5,281–2,704 kg ha^?1) due to differences in soil water contents. Water productivity varied from 1.05 to 1.34 kg m^?3, among the treatments in 3 years. The interactive effect of irrigation × tillage practices and irrigation × FYM on grain yield was significant. Yield performance proved that deficit irrigation (ETd₂) subjected to 75 % soil water deficit had the smallest yield decline with significant water saving would be the most appropriate irrigation level for wheat production in arid regions.     

Soil management and traffic effects on infiltration of irrigation water applied using sprinklers

Zero tillage and controlled traffic have been proposed as means for more productive and sustainable irrigated farming. Both practices affect soil infiltration characteristics and, therefore, should have effects on sprinkler irrigation performance. This study compared water infiltration and runoff in three sprinkler irrigation tests performed on an alluvial loam soil at different times during a maize (Zea mays L.)–cotton (Gossypium hirstium L.) rotation under two soil managements: permanent beds with crop residue retention (PB: planting beds maintained unaltered from year to year) and conventional beds with residues incorporated with tillage (CB: disc and chisel ploughing followed by rotavator pass and bed forming every year). Traffic was controlled and two types of furrows were distinguished in both tillage systems: with (+T) and without (−T) wheel traffic. The irrigation tests were performed on maize at full cover, on bare soil just before cotton sowing and on cotton with 50% ground cover. Infiltration and runoff were affected notably by both traffic and soil management. The soil under PB infiltrated more water than under CB, and −T furrows more than +T furrows. Considering the combined treatments, −T furrows in the CB system infiltrated more water than +T furrows in the PB system. A sprinkler irrigation model for simulating water application and soil infiltration and runoff was formulated. The model was used to analyse irrigation performance under infiltration characteristic of the CB and PB systems in trafficked and non-trafficked furrows. Five irrigation performance indicators were used to assess the various combinations of tillage and traffic: Wilkox–Swailes coefficient of uniformity; application efficiency; deep percolation ratio; tail water ratio; and adequacy. The model was used to develop operation diagrams and provided guidelines for making irrigation decisions in the new controlled traffic/permanent bed system and in a standard conventional system.     

不同粉垄深度和春灌灌水量对土壤水盐运移规律影响研究

为了解决南疆干旱区盐碱地改良问题,探讨不同粉垄深度和灌水量在春灌期间对土壤的水盐运移规律.基于新疆图木舒克市盐碱地试验田,以传统翻耕CK(20 cm)为对照,设置3个粉垄深度S1(40 cm)、S2(60 cm)、S3(80 cm)和3个灌水量W1(2400 m3/hm2)、W2(3000 m3/hm2),W3(360...     

Evaluation of humic substances fertigation through surface and subsurface drip irrigation systems on potato grown under Egyptian sandy soil conditions

The aim of this study was to evaluate the effect of humic substances application in sandy soil under surface and subsurface drip irrigation systems on potato tubers yield quantity, quality, nutrients concentration in tubers and soil fertility after harvesting. For this purpose, field experiment was carried out at the experimental farm of the Agricultural Research Station, National Research Center, El-Nubaria district, Egypt during the winter season of 2007/2008. The used experimental design was split plot design with three replicates, main treatments were presented irrigation systems, i.e. surface and subsurface drip irrigation, while subtreatments were presented rates of humic substances additives which were 0, 60 and 120 kg ha⁻¹. Results showed that increasing humic substances application rates up to 120 kg ha⁻¹ enhanced tubers yield quantity, starch content and total soluble solids. The increase of humic substances application rates was associated with the decrease of nutrients leaching, which was reflected on increasing macro- and micronutrients concentration in potato tubers, as well as increasing concentration of these nutrients in soil after tubers harvesting. Subsurface drip irrigation system was found to be more efficient than surface drip irrigation system on improving tubers yield quantity, quality parameters and nutrients concentration content, in addition to soil fertility after harvesting.     

Long term use of saline water for irrigation

Use of saline drainage water in irrigated agriculture, as a means of its disposal, was evaluated on a 60 ha site on the west side of the San Joaquin Valley. In the drip irrigation treatments, 50 to 59% of the irrigation water applied during the six-year rotation was saline with an EC_w ranging from 7 to 8 dS/m, and containing 5 to 7 mg/L boron and 220 to 310 g/L total selenium. Low salinity water with an EC_w of 0.4 to 0.5 dS/m and B 0.4 mg/1 was used to irrigate the furrow plots from 1982 to 1985 after which a blend of good quality water and saline drainage water was used. A six-year rotation of cotton, cotton, cotton, wheat, sugar beet and cotton was used. While the cotton and sugar beet yields were not affected during the initial six years, the levels of boron (B) in the soil became quite high and were accumulated in plant tissue to near toxic levels. During the six year period, for treatments surface irrigated with saline drainage water or a blend of saline and low salinity water, the B concentration in the soil increased throughout the 1.5 m soil profile while the electrical conductivity (EC_e) increased primarily in the upper l m of the profile. Increaszs in soil EC_e during the entire rotation occurred on plots where minimal leaching was practiced. Potential problems with germination and seedling establishment associated with increased surface soil salinity were avoided by leaching with rainfall and low-salinity pre-plant irrigations of 150 mm or more. Accumulation of boron and selenium poses a major threat to the sustainability of agriculture if drainage volumes are to be reduced by using drainage water for irrigation. This is particularly true in areas where toxic materials (salt, boron, other toxic minor elements) cannot be removed from the irrigated area. Continual storage within the root zone of the cropped soil is not sustainable.     

Yield and water relations of wheat as influenced by irrigation and depth of tillage

Summary Development of a ploughpan has been reported in Bangladesh for almost all ploughed soils which are puddled for transplanted rice cultivation. Field information on the water requirement of dryland crops such as wheat and the effects of loosening the dense layer on crop yield and water use efficiency are very limited. Field experiments were, therefore, conducted in the grey floodplain soil of Sonatala series (Aeric Haplaquept) to study the irrigation and tillage effects on the yield and water relations of wheat (Triticum aestivum L. cv. Sonalika). The split plot design experiment comprised four irrigation treatments in the mainplots viz. W₀ = no irrigation, W₁ = irrigation of 5 cm at 4 weeks after planting, W₂-W₁ + irrigation(s) of 5 cm each at irrigation water to cummulative pan evaporation (IW/CPE) ratio of 0.75 and W₃- W₁ + irrigation(s) of 5 cm eacht at IW/CPE ratio of 0.50. The sub-plot tillage depth treatments were: A-7.5 cm (traditional), B-15 cm, C-22.5 cm, D-22.5 cm practised in alternate wheat seasons. Measurements were made of grain and straw yield, soil water depletion and water expense efficiency.Irrigation had no effect on grain or straw yield. Tillage to 15 cm increased wheat yield by about 15% over traditional depth to ploughing. In general, deep tillage coupled with one irrigation at four weeks after planting produced the largest wheat yield.Soil water depletion (SWD) in the 0–90 cm profile was greatest in the treatment receiving two irrigations, one at 4 weeks and again at IW/CPE ratio of 0.50. The average SWD in this treatment was 113 in 1982–83 and 82 mm in 1983–84. Plots receiving traditional tillage (7.5 cm) had the greatest SWD. Total water expense were the greatest in treatments receiving three irrigations. The maximum water expense efficiency (WEE) of wheat was observed in the non-irrigated plots in 1982–83 and 1983–84, respectively. Deep tillage treatments, in general, had significantly greater WEE than those under traditional ploughing. Intensive irrigation and efficient soil and water management are important factors in enhancing crop productivity. The former not only permits judicious water use but also better utilization of other production factors thereby leading to increased crop yield which, in turn, helps stabilize the farming economy. The best way to meet increasing demand for water is to adopt efficient water management practices to increase water use efficiency.Irrigation should aim at restoring the soil water in the root zone to a level at which the crop can fully meet its evapo-transpiration (ET) requirement. The amount of water to be applied at each irrigation and how often a soil should be irrigated depend, however, on several factors such as the degree of soil water deficit before irrigation, soil types, crops, and climatic conditions (Chaudhury and Gupta 1980).Knowledge of movement of water through the soil is imperative to efficient water management and utilization. The presence of a dense pan impedes water movement into the sub-soil. As a result, the top soil becomes saturated by irrigation and sensitive dryland crops can fail as this plough layer impedes the penetration of roots into deeper soil layers and decreases water extraction. Crops growing in these soils often undergo severe water stress within 5–8 days after rainfall or irrigation (Lowry et al. 1970). Due to decrease rates of water flow, the lower soil layer may remain unsaturated and as a result, the recharge and soil water storage in the profile are considerably decreased (Sur et al. 1981).In Bangladesh, ploughpans develop to varying degree in almost all ploughed soils (Brammer 1980). They are particularly marked in soils which are puddled for transplanted rice cultivation where the pan is usually only 8–10 cm below the soil surface and 3–5 cm thick. Its presence is generally regarded as advantageous for cultivation of transplanted rice in that it prevents excessive deep percolation losses of water. But in the same soil this cultivation for a subsequent dryland crop would adversely affect yield. A slight modification of the plough layer could enable good yields of both rice and a dryland crop to be obtained in the same soil in different seasons (Brammer 1980). The sub soils have a good bearing capacity, both when wet and dry and the pan can easily be reformed, if desired, for cultivating transplanted rice after a dryland crop like wheat.Professor of Soil Science, Dhaka University, Dhaka, Bangladesh     

Sugar beet production as influenced by limited irrigation

Summary Sugar beets (Beta vulgaris L.) were grown on a Millville silt loam soil at Logan, Utah to study the relationships between yield (total dry matter, fresh root, and sucrose) and various levels of irrigation simulating different types of limited irrigation under drought conditions. There were four harvest dates. A model, PLANTGRO, was tested for yield prediction under the imposed conditions. A line source sprinkler irrigation system which applied irrigation water from an excess to a zero amount, was used to impose the various levels of irrigation. Irrigation was continued throughout the season on half of the area and terminated at mid-season on the other half. For both irrigation treatments, yield responses to irrigation levels were large. Unlike continuous irrigation throughout the season, when irrigation was terminated in mid-season, there was no increase in yield (total dry matter, fresh root, or sucrose) from harvest 1 to harvest 4. The relation of yield to termination of irrigation depended on the amount of stored soil water at the time of termination. Yield and relative yield exhibited a strong linear relationship with ET. Percent sucrose was not significantly affected by irrigation regimes or harvest date, but tended to increase as amount of applied irrigation water increased. The model PLANTGRO gave good predictions for relative yields of fresh roots, sucrose, and total dry matter under full-season irrigation. The relative yield relations of fresh roots, sucrose and total dry matter were similar. Where irrigation was terminated in mid-season the model slightly under-predicted yield at high irrigation levels.Contribution from Utah Agricultural Experiment Station, Utah State University, UT 84322, USA     

The effect of high sodium irrigation water on soil salinity and yield of mature grapefruit orchard

Summary Citrus is considered to be specifically sensitive to chloride and sodium, yet little data exist to show the effect of these ions on yield. An experiment was started in 1978 to study the effect of sodic irrigation water on yield. The treatments were SAR of the irrigation water of 2.8-(L), 5.5-(M), and 10.3-(H) (mol/m³)^1/2 . The experiment follows a study on the same plots using irrigation water of variable chloride concentration and a uniform SAR of 4.2 (mol/m³)^1/2.The high SAR, high Cl water resulted in a yield reduction of 9% from the control treatment. This reduction was similar to the reduction observed when only Cl was a variable. Total water uptake was reduced as salt concentration in the soil increased. The average water uptake for the four irrigation seasons 1978 to 1981 was 1025 mm, 953 mm and 823 mm for the L, M and H treatments, respectively.Soil ESP was increased as a result of sodium accumulation in the soil profile in the M and H treatments, while Cl and EC remained relatively constant with time during the experiment. After four years of irrigation the infiltration capacity values were 0.26, 0.17 and 0.16 cm/h for the L, M and H treatments, respectively. Fruit quality was not affected by the treatments.No specific toxicity symptoms were observed when the Na concentration in the soil saturation extract was 16 mol/m³ and the ESP was 8.0. The results lead to the conclusion that within the range used in this experiment the high ESP did not specifically effect yield and that yield response was due to the total salt concentration in the soil.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 626-E, 1982 series     

Barley yield response to irrigation and potential profits in the Texas High Plains

Summary Irrigated winter barley (Hordeum vulgare L.) can be a profitable alternative to some low profit major crops in the Texas High Plains. A six-year evaluation of yield response related to total spring irrigation water, applied by surface methods (furrow), and seasonal precipitation resulted in a multivariate function explaining 74% of the yield variation. Predicted yields varied from a low of 3.69 Mg ha^–1 to a maximum 6.18 Mg ha^–1 with 0 and 389 mm, respectively, based on average monthly precipitation quantities. Precipitation is skewed to less than average in th semi-arid Texas High Plains. Using modal precipitation amounts of 40% of average precipitation, yield estimates were reduced to 2.29 Mg ha^–1 with zero spring irrigation and to 5.63 Mg ha^–1 at the peak with 450 mm. A second multivariate yield response function related to alternative timings of single and multiple spring irrigations explained 76% of the variation in yields. Among all combinations of 1, 2, 3, and 4 spring irrigations, irrigation water-use efficiency was estimated to be highest with one application at the boot stage of development. All other single and combinations of multiple irrigations resulted in lower water-use efficiencies. A comparison of enterprise budgets of four irrigation timing alternatives and levels of application indicated highest profit over variable costs, $ 287 ha^–1, was attained by applying a total of 307 mm in three spring applications at the boot, head, and milk stages. A lower level of 217 mm applied at boot and milk stages was $ 12 ha^–1 less profitable and a higher level of 425 mm was $ 24 ha^–1 less profitable. When fixed costs of irrigation facilities, land, and machinery were considered, returns to management and risk were highest, $ 101 ha^–1, with 217 mm. Using 40% of average precipitation, profits were reduced $ 65 ha^–1 with 217 mm and $ 69 ha^–1 with 307 mm spring irrigation levels.Respectively, agricultural economist, research scientist, and research associate, Texas Agr. Exp. Station, Amarillo, Texas; Emeritus Extension agronomist, Texas Agr. Ext. Service, Amarillo, Texas; agricultural engineer, Texas Agr. Exp. Station, Amarillo, Texas     

Infiltration and runoff as affected by pitting,mulching and sprinkler irrigation

Summary Changes in infiltration and runoff caused by pitting and mulching under sprinkler irrigation were studied on two soil types. Pitting or diking was done with an implement called a dammer-diker. Five soil treatments were applied: shallow and deep dammer-diker, shallow dammer-diker with mulch, bare, and a mulched soil, combined with two water application rates. Total water infiltration and runoff varied during the experiment. Runoff decreased with area of water storage provided by the pits and the less water was applied. Mulch treatments also reduced runoff. Surface water storage decreased during the season. Changes in soil physical properties due to pitting were more important in controlling runoff than surface water storage.The effective saturated hydraulic conductivity of the soil progressively decreased through the season for all soil treatments and water application rates.A model was developed to simulate the effect of pits on runoff. On a silt loam soil, simulated percent runoff and accumulated runoff over time for the bare and pitted treatments agreed closely to measured values. The agreement of simulated to measured runoff for a silty clay loam soil was not as good probably because of cracking which the simulation model did not take into account.     

Landscape irrigation scheduling efficiency and adequacy by various control technologies

Automated residential irrigation systems tend to result in higher water use than non-automated systems. Increasing the scheduling efficiency of an automated irrigation system provides the opportunity to conserve water resources while maintaining good landscape quality. Control technologies available for reducing over-irrigation include evapotranspiration (ET) based controllers, soil moisture sensor (SMS) controllers, and rain sensors (RS). The purpose of this research was to evaluate the capability of these control technologies to schedule irrigation compared to a soil water balance model based on the Irrigation Association (IA) Smart Water Application Technologies (SWAT) testing protocol. Irrigation adequacy and scheduling efficiency were calculated in 30-day running totals to determine the amount of over- or under-irrigation for each control technology based on the IA SWAT testing protocol. A time-based treatment with irrigation 2 days/week and no rain sensor (NRS) was established as a comparison. In general, the irrigation adequacy ratings (measure of under-irrigation) for the treatments were higher during the fall months of testing than the spring months due to lower ET resulting in lower irrigation demand. Scheduling efficiency values (measure of over-irrigation) decreased for all treatments when rainfall increased. During the rainy period of this testing, total rainfall was almost double reference evapotranspiration (ET_o) while in the remaining three testing periods the opposite was true. The 30-day irrigation adequacy values, considering all treatments, varied during the testing periods by 0-68 percentile points. Looking at only one 30-day testing period, as is done in the IA SWAT testing protocol, will not fully capture the performance of an irrigation controller. Scheduling efficiency alone was not a good indicator of controller performance. The amount of water applied and the timing of application were both important to maintaining acceptable turfgrass quality and receiving good irrigation adequacy and scheduling efficiency scores.     

Water relations,growth and yield of Fino lemon trees under regulated deficit irrigation

Fino lemon trees (Citrus limon L. Burm. fil.) on sour orange (Citrus aurantium L.), growing on a low water retention capacity soil, were submitted to three different irrigation treatments over four years: 100% ETc all year (T-0), 25% ETc all year except during the rapid fruit growth period when 100% ETc was applied (T-1) and 100% ETc all year, except during the rapid fruit growth period when 70% ETc was applied (T-2). A water saving of 30 and 20% was achieved in the T-1 and T-2 treatments, respectively. The plant responses to irrigation treatments were similar in all the years studied. Leaf water potential decreased during deficit irrigation periods in T-1 and T-2 treatments. Larger differences were found in values taken at predawn ( _pd) than at midday ( _md), indicating that _pd is a more useful indicator of plant water status. There was neither osmotic nor elastic adjustment in response to deficit irrigation treatment. A clear separation between the main periods of shoot and fruit growth was found, which can be considered an advantageous characteristic in applying regulated deficit irrigation strategies. Onset of the critical period of rapid fruit growth could be determined precisely by considering the decrease in relative fruit growth rate values. T-2 treatment did not induce a significant reduction in total yield, but it caused a delay in reaching marketable lemon fruit size. T-1 treatment did not affect total yield, with a reduction in yield on the first pick occurring in only one year. Chemical characteristics of lemon fruit were not significantly modified by irrigation treatment.     

Drip irrigation of cotton with saline-sodic water

Summary A two-year study was conducted in the Negev region of Israel, using the drip method, to determine the effect of four levels of water quality (EC =1.0, 3.2, 5.4 and 7.3 dS/m) in combination with three soil amendment treatments (gypsum spread on the soil surface along the drip laterals after planting, injection of H₂SO₄ into the water during each irrigation, and a control) on plant response, salt distribution in the soil profile, and soil sodification processes. Salinity did not reduce yields even at the highest level, in spite of sodium and chloride accumulation. The highest seed cotton yield (6.4 t/ha) was obtained with the local well water (EC =3.2 dS/m), indicating an optimal response to salinity. The addition of soil amendments during the irrigation season, although reducing exchangeable sodium accumulation near the emitter, endangers the next crop by increasing sodium accumulation under the plant row. It is therefore, recommended that the amendment be applied only before the winter.Contribution from the Agricultural Research Organization, Israel. No. 1131-E, 1984 series     

Response of Salustiana oranges to high frequency deficit irrigation

Summary Mature Salustiana orange trees under drip irrigation were subjected to deficit irrigation during three years. The water applied (including effective rainfall) in the five irrigation treatments was: (A) 60% of the evaporation of a Class A pan over irrigated grass (Control treatment); B) and C 80% and 60% of control, during the whole year, respectively; (D) 60% of control during the flowering and fruit set period; (E) 60% of control during the fruit maturation period. During the rest of the year, treatments D and E received the same amount of water as the control. There were four replicates in a completely randomized block design. Irrigation frequency was the same for all treatments. Crop evapotranspiration (ET) was estimated by the water balance method using a neutron moisture meter. ET for the control treatment was about 840 mm/year and it was reduced in the deficit treatments. Irrigation treatments affected both yield and fruit quality although the effects varied between years according to the season's rainfall. Fruit number was not affected by the irrigation treatments, therefore differences in yield were due to effect on average fruit weight. Compared to the control treatment, treatments B and C decreased yield significantly (p = 0.05) by 5% and 15%, respectively, and increased the total soluble solids and acids content of the fruit juice. Water deficit in the flowering and fruit set period (treatment D) decreased yield by 4%, acids content of the juice and peel thickness. Treatment E produced fruit of lower quality with thicker peel and more acids than the control. Treatments did not affect juice and pulp content, maturity index of fruits nor maturation time. The effects of the irrigation treatments on the water status of the trees, fruit set and abscission and their implications on irrigation scheduling are also discussed.     

Effect of nozzle type on runoff and yield of corn and sorghum under center pivot sprinkler systems

Summary Corn (Zea mays L.) and grain sorghum (Sorghum bicolor L.) production were compared under impact and spray nozzled center pivot sprinkler systems. The crops were grown under two pairs of sprinkler systems located approximately 110 km apart. One system of each pair was equipped with high pressure (379 or 414 kPa) impact sprinkler heads and the other system was equipped with low pressure (172 or 207 kPa) spray nozzles. Half of each circle was planted to corn and half was planted to sorghum. Additionally, four tillage treatments were included in the experimental design (conventional tillage, conventional tillage + deep ripping, conventional tillage + diking, and minimum tillage). The evaporative losses from the high pressure system with impact sprinkler heads were not significantly different from the low pressure system with spray nozzles. The minimum tillage and deep ripped treatments reduced runoff while diking eliminated it. The two nozzle types did not produce significantly different grain sorghum yields; however, corn yielded significantly more under the high pressure system with impact sprinkler heads than under the low pressure system with spray nozzles. The different tillage treatments did not influence yields of either crop significantly.Contribution of the Texas Agricultural Experiment Station. Paper No. 19198     

Irrigation effects on rooting patterns of Spring Barley

Summary The objective of this experiment was to quantitatively describe, on three dates throughout the growing season, the rooting patterns of spring barley (Hordeum vulgare L.) growing under an irrigation gradient on a clay loam soil (clayey over loamy, montmorillonitic (calcareous), thermic Vertic Torrifluvent) as Las Cruces, New Mexico. Evapotranspiration (E_t) was calculated at 15 locations along the gradient, using the water balance method, and ranged from 320 to 565 mm in 1982 and 320 to 575 mm in 1983. Roots were first sampled before the irrigation treatments were started when the crop was in the tillering or jointing stage; secondly, in the middle of the growing season after heading, and finally at maturity. Soil was sampled in 0.15 m increments to a depth of 1.2 m at each location using a soil tube. Roots were extracted from the soil using a saline water flotation method. Total above-ground biomass was determined at maturity.Journal Article 1243, Agricultural Experiment Station, New Mexico State University, Las Cruces, NM 88003, USA