Cm Of Irrigation Water Research Articles

Impact of different quantity and quality of irrigation water on crop yield and biomass of winter maize using FAO-Aqua crop model

Irrigation has a major role to play in the productivity of winter maize. Precise information about the quantity and quality of irrigation water is the key for higher productivity of winter maize. In the present study attempt has been made to asses the impact of different depth of irrigation water on crop yield and biomass of winter maize using FAO-Aquacrop Model. In the first case crop yield and biomass was simulated for irrigation water depth varied from 20 mm to 80 mm, keeping the irrigation water quality constant. Similarly, in another case the optimum irrigation depth was kept constant and irrigation water quality varied from 1 to 10 ds/m. The simulated crop yield and biomass increases up to 40 cm depth of irrigation water application for all three seasons. When a similar comparison was made for 30 cm depth of irrigation water application the simulated yield reduction was only 0.79%, 2.2% and 2.4 % for the year 2016-17, 2017-18 and 2018-19 respectively. The analysis suggested that this yield reduction can easily be compromised for saving 10 cm of irrigation water. This study indicated that 30 cm depth of irrigation water is optimum for Winter maize in BurhiGandak river basin of North Bihar In case of deficit irrigation of 20 cm depth of irrigation water application the simulated yield reduced by 14.4 %, 25.4 % and 11.4 % for the year 2016-17, 2017-18 and 2018-19 respectively. Assessment of response of different quality irrigation water on simulated crop yield and biomass of winter maize using FAO-Aquacrop model suggests that simulated yield was found maximum with 1 ds/m. The reduction in simulated yield with 10 ds/m water quality was observed maximum with a value of 41.3 %, 44.4 % and 38.4 % respectively for the year 2016-17, 2017-18 and 2018-19. FAO-Aquacrop model can be used as an important tool for efficient planning of irrigation water under diminishing water supply and deteriorating water quality.

Performance of rice (Oryza sativa) cultivars as influenced by irrigation regimes and establishment methods

The present study was carried out at Punjab Agricultural University, Ludhiana during kharif 2016 and 2017 to compare economics, energetics, crop and water productivity of rice (Oryza sativa L.) cultivars grown under variable irrigation regimes and crop establishment methods. Results revealed that the rice variety PR 126 produced 22.6 and 23.3% higher grain yield than PR 115 and PR 124, respectively. Scheduling irrigation at 2 days after infiltration of ponded water (DAIPW) in puddled transplanted rice (PTR) resulted in highest grain yield (7.07 t/ha), which was statistically similar to irrigation at 3 DAIPW in PTR (6.96 t/ha), but significantly higher than direct seeded rice (DSR) irrigated at 2, 4, 6 and 8 DAIPW. The interaction between cultivars and establishment-irrigation regimes showed that PR 126 performed statistically equal under PTR and DSR conditions at all irrigation regimes except 6 and 8 DAIPW. However, maximum net returns and B:C was obtained from PR 126 when puddled transplanted and irrigated at 2 DAIWP. PR 124 irrigated at 2 DAIPW in PTR consumed maximum amount of irrigation water (130.3 cm). Compared to that, PR 126 when direct seeded and irrigated at 4 DAIPW saved 42.8 cm of irrigation water and registered 43, 30.2, 6.6 and 6.3% higher apparent crop water productivity, total crop water productivity, energy use efficiency and energy productivity, respectively with statistically similar grain yield and B:C.

Modelling Water Productivity of Selected Grain Crops in Rain-fed and Surface Irrigated Fields in Northern Nigeria

Field trials of selected grain crops (rice, wheat and maize) were conducted for three years under rain-fed and surface irrigated systems to evaluate their water productivity and model same. A completely randomized design (CRD) experiment was used at the Irrigation Research Station, Kadawa, Kano State. Rice yield was 11.6, 9.9 and 5.3 tons/ha; wheat yield was 1.46, 1.92 and 2.0 tons/ha, while Maize yield was 0.8, 0.4 and 0.91 tons/ha in the 2009/2010, 2010/2011 and 2011/2012 cropping season, respectively. ANOVA revealed a highly significant difference in the yield of paddy rice, wheat and maize at both 1 % and 5% significant levels (Fcalc>Ftab), with p-value of 0.0002, 0.004 and 0.001 for rice, wheat and maize respectively. Crop – water productivity models developed revealed that optimum crop yield of 12.8 tons/ha of paddy rice, 2.7 tons/ha of wheat and 0.94 tons/ha of maize is achievable with 58.3 cm of rainfall, 34 cm and of 29.8 cm of irrigation water respectively.

Leaching Behavior of Two Pendimethalin Formulations in a Soilless Growing Medium

Pendimethalin is commonly applied for PRE weed control in container nursery production. Field and laboratory trials were conducted to determine herbicide effectiveness and leaching of two pendimethalin formulations in pine bark, the primary component used in the growing medium of container-grown plants in the South. The microencapsulated (ME) formulation of pendimethalin gave lower control of southern crabgrass and leached deeper than the emulsifiable concentrate (EC) formulation in pine bark. The EC formulation controlled southern crabgrass 93% compared with only 70% with the ME formulation at 4.48 kg ai ha−1. After applying 3.4 kg ai ha−1pendimethalin and 17.8 cm of irrigation water, the ME formulation showed greater leaching into the 3- to 6- and 6- to 9-cm depths than the EC formulation on the basis of a southern crabgrass bioassay. Using a microwave extraction method, only 0.91 mg kg−1pendimethalin was found in the 3- to 6-cm pine bark depth compared with 4.0 mg kg−1for the ME formulation. Below the 6-cm depth, no pendimethalin was detected when the EC formulation was applied, but 0.5 ppm was found for the ME formulation. No pendimethalin was detected in effluent collected from irrigation water for the EC; however, 3.0 mg kg−1was collected from leachate for the ME formulation. Pendimethalin ME is leaching much deeper than the EC formulation in the pine bark profile, which results in lower weed control. This extensive leaching of ME formulation may be due to capsule movement with the irrigation water, combined with a delayed release of pendimethalin, which then binds to the pine bark much lower in the container profile.

An economic analysis of role of technology in sustaining water resources for enhanced agricultural production

Sugar producing regions in India have more than 80 percentage groundwater irrigation through deep-well pumping. Whereas, NASA's gravity recovery and climate experiment satellites have revealed faster depletion of groundwater stocks in India. These areas are cultivating 93 percentage of sugarcane. This research is a comparative study and has attempted to estimate the economic value of irrigation water and the benefits of water and energy that can be saved through adoption of improved irrigation technologies. The economic value of each ha. cm of irrigation water for sugarcane was also worked out. Including additional area under irrigation with the water saved should be recommended only in safe and semi-critical regions to prevent 'rebound' effect.

SIGNIFICANCE OF NO- AND CONVENTIONAL TILLAGE IN COMBINATION WITH SOME LOCAL NATURAL AMENDMENTS AS RELATED TO SOIL PHYSICO-CHEMICAL PROPERTIES AND WHEAT PRODUCTIVTY IRRIGATED WITH LOW QAULITY WATER

A field experiment was conducted at Tamaya district, El-FayoumGovernorate, Egypt during two successive to seasons of 2008-2009/2009-2010 to evaluate the effect of either no- or conventional tillage practices assolely treatments or applied mineral N and P fertilizers alone or conjunctionwith some local natural amendments, i.e., gypsum, farmyard manure andfilter mud for ameliorating some soil properties, i.e., organic matter content,pH, infiltration rate and moisture retention as well as grain yield of wheat(Triticum aestivum L., Sakha 69 cv.) plants as a next crop after rice (Oryzasativa L., Giza 176 cv.) and irrigated with a low quality of irrigation water.The obtained results showed that in case of no-tillage, the rice plantresidues of 10 cm height were left, and in turn caused an increase in each ofsoil organic matter content and infiltration rate vs a parallel decrease in soilpH value. The corresponding increase of soil organic matter content at theend of experiment reached 0.519 %, as a mean value for no-tillage vs 0.455% in case of the conventional tillage in soil depth of 0-15 cm. Suchpronounced increase in soil organic matter content positively reflected onwheat grain yield. Moreover, the grain yield was maximized with increasingthe applied doses of N and P fertilizers. These increases achieved anusefulness at no-tillage practice as compared to the conventional one duringthe first season of 2008-2009, while an opposite trend was occurred at thenext season of 2009-2010.Practically, 32.44 cm irrigation water was used per year in case of notillage practice vs 39.66 cm in case of the conventional one, with superiorityfor no-tillage that could be saved 7.22 cm of irrigation water. Finally, theresults emphasized the necessity of using 120 kg N + 25 kg P2O5/ha asfertilizer doses with farmyard manure or filter mud or gypsum under notillage practice for improving soil organic matter content and sustainingwheat-rice cropping sequence under the prevailing conditions of using lowquality of irrigation water.

Development of Clemson variable-rate lateral irrigation system

Crops in the Southern United States are generally produced in fields which are known to have a high degree of variability in soil type, water holding capacity, infiltration rates, and other major factors which affect crop production. In these fields, the ability to turn irrigation water on or off or apply variably to different segments of the field is advantageous over the conventional uniform application. A variable-rate lateral irrigation (VRLI) system was developed for site-specific application of water to match field variability. The system consists of solid-state relays controlled by custom software, air-actuated diaphragm valves, a forward speed control system and a GPS receiver. The Clemson VRLI system applies variable-rate water utilizing the nozzle-pulsing technique and variable speed control system. This system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Reference Network (CRN) data. Uniformity tests show that the system is able to control the irrigation rate from 0 to 2.5 cm of irrigation water and can control the forward speed between 145 and 29 m/h. The pulsing technique to deliver variable amounts of irrigation had little adverse effect on system uniformity and nozzle flow rate with an average application error of less than 2%.

Effect of subsurface drip irrigation on onion yield

Subsurface drip system is the latest method of irrigation. The design of subsurface drip system involves consideration of structure and texture of soil, and crop’s root development pattern. A 3-year experiment was conducted on onion (Allium Cepa L., cv. Creole Red) in a sandy loam soil from October to May in 2002–2003, 2003–2004 and 2004–2005 to study the effect of depth of placement of drip lateral and different levels of irrigation on yield. Tests for uniformity of water application through the system were carried out in December of each year. Three different irrigation levels of 60, 80 and 100% of the crop evapotranspiration and six placement depths of the drip laterals (surface (0), 5, 10, 15, 20 and 30 cm) were maintained in the study. Onion yield was significantly affected by the placement depth of the drip lateral. Maximum yield (25.7 t ha−1) was obtained by applying the 60.7 cm of irrigation water and by placing the drip lateral at 10 cm soil depth. Maximum irrigation water use efficiency (IWUE) (0.55 t ha−1 cm−1) was obtained by placing the drip lateral at 10 cm depth. The greater vertical movement of water in the sandy-loam soil took place because of the predominant role of gravity rather than that of the capillary forces. Therefore, placement of drip lateral at shallow depths is recommended in onion crop to get higher yield.

Tillage and residual organic manures/chemical amendment effects on soil organic matter and yield of wheat under sodic water irrigation

The effect of no-tillage (NT) and conventional tillage (CT) practices applied either with NP fertilizer alone or in conjunction with gypsum or farm yard manure (FYM) or sulphitation pressmud (SPM) were evaluated on soil organic carbon (SOC), soil pH, sodium absorption ratio (SAR), infiltration rate, water saving and grain yield of wheat grown with sodic water in rice ( Oryza sativa L.)–wheat ( Triticum aestivum L.) rotation at Central Soil Salinity Research Institute Research Farm, Kaithal, India. In NT treatment the residue of previous rice (15 cm height) crop was left on the surface whereas in CT treatment no crop residue was involved. NT practice increased SOC and infiltration rate in all treatments. The mean organic carbon in 0–15 cm soil layer at the end of study was 3.17 g kg −1 in NT treatment against 2.84 g kg −1 in CT treatment. Organic carbon improvement in NT treatment was reflected in grain yield increament. Soil pH was lower in NT than CT treatment. In general, wheat yield increased with the increase in nitrogen (N) and phosphorus (P) fertilizer doses. The grain yield in the NT treatment remained below the CT treatment during the first year (2001) but was greater than CT treatment during the next two years (2002 and 2003). However, the average yields data for the three years remained statistically non significant. In NT practice, 32.44 cm irrigation water was used each year as compared to 39.66 cm in CT practice. No-tillage, thus, saved 7.22 cm of irrigation water. The results emphasized the necessity of using N120P26 kg ha −1 fertilizers dose with FYM or SPM or gypsum under NT practice for improving soil organic matter and sustaining wheat production under condition of sodic water irrigation.

Effect of drip tape placement depth and irrigation level on yield of potato

Subsurface drip irrigation (SDI) is the most advanced method of irrigation, which enables the application of the small amounts of water to the soil through the drippers placed below the soil surface. One of the most commonly discussed aspects of SDI system is installation depth of drip lateral. Determining the appropriate depth of installation involves consideration of soil structure, texture, and crop's root development pattern. Site-wise and crop-wise variations of these parameters preclude the possibility of framing general recommendations for installation depths of SDI system. An experiment was conducted on potato (var. Kufri Anand) during October–February for 3 years (2002–2003, 2003–2004 and 2004–2005) to study the effect of depth of placement of drip tape and different levels of irrigation application on potato yield. Drip tapes were buried manually in the middle of different ridges. Tests for uniformity of water application through the SDI system were carried out in the month of October every year. Three different irrigation levels of 60, 80 and 100% of the crop evapotranspiration and five depths of placement of drip tape namely, 0.0, 5.0, 10.0, 15.0 and 20.0 cm were maintained in the study. The coefficient of variation (CV) of flow rates was found 0.046, 0.047 and 0.064 during 2002–2003, 2003–2004 and 2004–2005, respectively. The low CV indicated good performance of the SDI system throughout the cropping season. The values of statistical uniformity (SU) and distribution uniformity (DU) were more than 92.0% during all the three cropping seasons. Soil water distribution at different growth stages of potato under different depths of placement of drip tape for varying irrigation levels was monitored. When drip tape was placed at surface and buried at 5.0 cm soil depth, upward movement of water takes place, 21.5% soil water content was found throughout the crop season of potato. When drip tape was buried 10.0, 15.0 and 20.0 cm below the surface, upward water movement due to capillary forces was not sufficient and soil surface remained relatively dry. The maximum yield was recorded when drip tape was buried at 10.0 cm during 2002–2003 and 2004–2005 and at 15.0 cm during 2003–2004 that was followed by drip tape placement at 20.0, 10.0 and 5.0 cm depths in 2002–2003 to 2004–2005, respectively. Treatment 0.6T4 gave maximum IWUE of 2.07, 2.13 and 2.05 t ha −1 cm −1 during 2002–2003, 2003–2004 and 2004–2005, respectively. The highest benefit cost ratio of 1.7 was obtained for treatment T3. Lowest benefit–cost ratio of 0.9 was found for treatment 0.6T5. The cost incurred for the installation of drip tape at successively higher depths, increases the annual cost of production. The placement depth of drip tape significantly affected potato yield. Maximum yield was obtained by applying the 100% of the crop evapotranspiration (23.6 cm of irrigation water) and by placing the drip tape at 10.0 cm depth. In the sandy loam soil at the experimental site, the gravity force predominated over the capillary force causing a greater downward movement of water. Therefore, shallow depth of placement of drip tape (10.0 cm) was recommended in potato crop to get higher yield. Appropriate depth of placement of drip tape however, will differ with crop and the change in soil type.

Non-irrigation in Fall and Winter Improves Florida Citrus Fruit Quality

Moderate water stress applied to citrus trees can increase fruit °Brix. Florida citrus growers have been required to use less irrigation as competition for water increases. The goal of this study was to see if irrigation could be eliminated in the fall and winter with few negative consequences. Water stress was imposed over a 3-year period on `Hamlin' and `Valencia' oranges (an early and late variety, respectively) by stopping irrigation in late October and restarting it in March. `Hamlin' fruit was harvested after 2 months of stress and `Valencia' fruit was harvested after 4 to 5 months of stress. In most years, °Brix was increased by water stress. Over a 3-year period, `Hamlin' yield was not affected by the water stress, but `Valencia' yield decreased slightly in the 3rd year. The increase in °Brix is beneficial economically, and, over 3 cm of irrigation water per year can be saved.

Sensitivity of Selected Crops to Isoxaflutole in Soil and Irrigation Water

Isoxaflutole, a preemergence herbicide for use in corn, causes bleaching of plant tissue and plant death at low rates. A concern regarding widespread use of isoxaflutole is the unintentional exposure of high-value, minor hectareage crops that may be sensitive. Unintentional exposure could occur because of carryover from a previous application, spray drift, or contamination of irrigation water. The objective of this study was to determine the potential for injury to nine minor hectareage Michigan crops. Crops evaluated were: adzuki bean, alfalfa, carrot, cucumber, dry bean (navy and black beans), onion, sugar beet, and tomato. Experiments were conducted in the greenhouse to evaluate injury from low rates of isoxaflutole applied to soil to simulate carryover as well as low concentrations of isoxaflutole in 2.54 cm of irrigation water applied over the course of 1 h to 15-cm-tall plants. Isoxaflutole rates and concentrations that cause 20% injury (I20) were calculated using Seefeldt's log-logistic dose–response model. Regardless of application type, onion was always the least sensitive plant to isoxaflutole (I20= 37 g/ha applied to soil and 194 μg/L in irrigation water), whereas navy bean and black bean were the most sensitive (I20= 9 g/ha applied to soil and 5 μg/ L in irrigation water). The remaining plants exhibited intermediate sensitivity. All of the rates that resulted in injury were substantially less than the rates used for weed control in corn. Carryover from isoxaflutole applications in corn production may require plant back restrictions for certain sensitive crops.

Effect of Irrigation on the Efficacy of Insecticides for Controlling Two Species of Mole Crickets (Orthoptera: Gryllotalpidae) on Golf Courses

Effects of irrigation regimen, quantity, and timing on the efficacy of three insecticides for controlling nymphs of the southern mole cricket, Scapteriscus borellii Giglio-Tos, and the tawny mole cricket, Scapteriscus vicinus Scudder, were studied on golf courses in 1997, 1998, and 1999. Two irrigation regimen tests using two rates of bifenthrin and lambda-cyhalothrin produced inconclusive results. Mole cricket damage ratings after the applications of bifenthrin (60 g [AI]/ha) and lambda-cyhalothrin (76 g [AI]/ha) were not significantly different among the four irrigation regimens (non-irrigation, irrigation before treatment, irrigation after treatment, and irrigation before and after treatment). Mole cricket damage rating after the application of bifenthrin (120 g [AI]/ha) under irrigation before and after irrigation was significantly better than those under other irrigation regimens at 14 and 21 d after treatment (DAT). Different irrigation quantity and irrigation timing (after insecticide treatment) did not significantly affect the performance of imidacloprid (434 g [AI]/ha) in the 1998 tests. However, the results from the 1999 test indicated that mole cricket damage ratings from the imidacloprid-treated plots were significantly different between 2 and 0.5 cm irrigation water after treatment at 21 and 28 DAT. Application of bifenthrin at a rate of 120 g (AI)/ha with 0.5 cm of irrigation water after treatment resulted in significantly lower mole cricket damage ratings than those of 1.0 and 2.0 cm of irrigation water after treatment at 30 DAT only in the 1998 test. Bifenthrin with irrigation at 1 h after insecticide treatment provided better mole cricket control than that of irrigation at 5 min after treatment at 30 DAT only in the 1998 test. Mole cricket damage ratings after application of bifenthrin were not significantly different between either irrigation quantity treatment or irrigation timing treatment in the 1999 tests. Possible effects of application timing, environmental conditions, irrigation practice, and insecticide physical properties on the results are discussed.

Bromide transport under sprinkler and flood irrigation for no-till soil condition

Understanding the influence of irrigation methods on solute transport is essential to properly manage chemical use in agricultural soils. In this study, we compare the transport of a conservative solute (bromide) under sprinkler and flood irrigations on a sandy clay loam (mixed Ustollic Haplargid) under no-till condition. After spraying 148.8 kg/ha of KBr on the surface, ≈25 cm of irrigation water was applied in six increments over two months as flood irrigation on one plot and as sprinkler irrigation on another plot. The net applied water (NAW=irrigation+precipitation−evaporation) was similar for both plots, which allowed the comparison of the Br profiles for the two types of irrigation. Water content and Br concentration were sampled at 5, 19, 34, and 68 days after chemical application. The recovered mass of Br and the location of center of mass were comparable for the two types of irrigation. The spread around the center of mass, however, was higher for the flood-irrigated plot. On the flood-irrigated plot, more mass leached below the depth of 90 cm, with the differences being statistically significant. The velocity of the Br center of mass was consistently 10%–20% larger than the piston displacement velocity. Dispersion and velocity coefficients varied substantially between sampling time. A recent quasi-steady solution of the convection–dispersion equation [M.H. Nachabe, L.R. Ahuja, Quasi-analytical solution for predicting the redistribution of surface-applied chemicals. Trans. ASAE 39(5) (1996) 1659–1664], which accounts for variable flow and dispersion, simulates the Br profiles fairly well.

Onion Irrigation and Nitrogen Leaching in the Arkansas Valley of Colorado 1990-1991

Water and nitrogen (N) are major inputs in the production of onions in the Arkansas Valley of Colorado. Because nitrates move with irrigation water, the effect of different rates of application of both N fertilizer and water on nitrate leaching were studied simultaneously. After a 2-year field study (1990-1991), it was concluded that >50 t·ha-1 of onions could be obtained without any N fertilizer when >42 ppm of nitrate nitrogen (NO3-N) were initially present in the top 33 cm of soil and up to 112 cm of irrigation water was applied. Total onion yield was not improved by applying more than the calculated irrigation requirement. The 2-m profile of soil under these experiments was found to contain >1400 kg·ha-1 of residual NO3-N prior to fertilizer treatments. When twice the estimated irrigation requirement was applied, >1000 kg·ha-1 of NO3-N was unaccounted for and presumed to have been mostly leached below the 2-m profile and partly denitrified. In both years, the onions were planted on land that had been fallowed the previous season, which does not help explain the presence of the high levels of nitrates found in the soil profile. It was concluded that sound water and N management practices in onion fields are crucial for preservation of water quality.

Soil and crop imrovement with water-soluble polymers

Summary The soil conditioner Krilium failed some 30 years ago because it was too expensive, too difficult to use, and the results were inconsistent. Advances in polymer chemistry have made possible a new generation of water-soluble polymers which with new application techniques can largely overcome the problems associated with Krilium. Some new polymers have molecular weights 100 or more times than Krilium, and for some purposes the application rate need be only 1/100 that used for Krilium. High efficiency of use can be obtained when water-soluble polymers are applied in irrigation water to newly tilled soil to stabilize existing aggregates. Experiments in which water-soluble polymers were applied in solution to seedbeds indicate that as little as 2 kg ha −1 prevents surface crusting of soil when at least 1/4 cm of irrigation water is applied with the polymer. Effective rates vary with clay content of soil and amount of soil organic matter. Some synergistic effects on plant growth are often observed when polymer and organic matter are applied to soil simultaneously. The physical properties of soil are improved throughout the plow depth with application rates somewhat higher than 2 kg ha −1 polymer with irrigation water carrier. Benefits include improved soil aeration, water conservation, and control of erosion of soil. Laboratory testing of soil helps to guide use of water-soluble polymers and can show which of cationic and anionic polymer should be used for a given soil. Some soils respond more if some soluble Ca is also applied.

Título en español

Se compararon distintos sistemas de regar arrozales cultivados intensivamente. Los rendimientos más altos se obtuvieron cuando la semilla se sembró en terreno seco, se tapó con tierra y enseguida se regó intermitentemente por 3 semanas, y luego se anegó permanentemente (7,020 kg de arroz en cáscara/ha). Se obtuvo una producción más baja, 5,300 kg/ha, cuando se sembró semilla pregerminada en terreno inundado permanentemente. Este sistema puede practicarse cuando la condición del terreno no permite usar el sistema anterior. En tal caso es aconsejable desaguar los campos unos 3 días después de la siembra o inmediatamente, si mucha de la semilla flotase. En este caso, se debe regar a intervalos durante aproximadamente 3 semanas y luego inundar los campos permanentemente. Si los campos se mantienen inundados después de sembrar se pueden combatir mejor los yerbajos y algunos insectos, pero las algas pueden constituir un serio problema. Además, si flota mucha de la semilla la plantación no será uniforme. No deben mantenerse más de unos 8 cm de agua sobre el terreno mientras las plantitas se desarrollan. Se obtuvo un buen rendimiento 6,830 kg/ha, regando intermitentemente durante todo el ciclo de producción. Este sistema permite sembrar arroz en terrenos que no se pueden inundar debido a su topografía o porosidad o donde no hay agua suficiente, ya que requiere menos agua. Sin embargo, es necesario combatir los yerbajos con más frecuencia.

A Severe Drought: Impact on Tree Growth, Phenology, Net Photosynthetic Rate and Water Relations

An unusually severe drought occurred in central Missouri during the summer of 1976. The drought resulted in an average soil water potential of ?26.1 bars in the upper 45 cm of soil profile in spite of the addition of 4.9 cm of irrigation water. It enabled us to examine its effects on phenology, growth and physiological processes, as well as the water relations of white oak (Quercus alba L. ), and eight other species found in this oak-hickory forest. The drought had a dramatic impact on base (presunrise) xylem pressure potential of white oak in both irrigated ( ? 19.6 to ?34.3 bars) and nonirrigated specimens ( ? 27.8 to ?45.2 bars). Growth was reduced, die-back increased, net photosynthetic rate was depressed to near the compensation point and phenological patterns in the following year (1977) were altered. An estimation of the number of days on which stornata were closed for most of the photoperiod was compared to the number of days when mature leaves were present. The following ranking of species based on this index of stomatal control was possible (from most to least time spent with stornata closed) : sunflower > flowering dogwood = hlack walnut > sugar maple > northern red oak > white oak =? eastern red cedar = black oak. Various drought avoidance mechanisms are also presented and discussed in regard to these eight species. The long periods of low soil water potentials and base xylem pressure potentials experienced during the drought of 1976 did not prevent the recovery of the growth processes that autumn or the subsequent spring. All study species seemed well-adapted to survival and to continued functioning during this severe drought.

Injection of Insecticide in Irrigation Water To Control Corn Earworm and Fall Armyworm on Corn

ABSTRACT A scaled one-nozzle irrigation system was con-structed and tested for injecting insecticide into irrigation water for control of insects attacking corn. In-secticide was injected either inside the sprinkler nozzle or at the intake of the irrigation pump. The two injection methods gave equal insect control. Also, the injection of water-soluble and non-soluble materials into the system gave equal results. A formulation composed of 2 L of oil plus 1 L of Sevin-4 oil resulted in the same insect control as Sevin-4 oil alone. Application of 0.36 cm of irrigation water after completion of insecticide treatments did not significantly affect kill of corn earworm, Heliothis zea (Boddie). Field tests indicated that corn treated with water-soluble methomyl had significantly more wormfree ears than corn treated with stirofos (tested as Gardona 80 per-cent in oil). Oil used by itself resulted in significantly less wormfree ears than Gardona in oil.

Effect of time of irrigation on the distribution of 1,2‐dibromo‐3‐chloropropane in soil after shallow injection

AbstractThe effect of irrigation time on the dispersion of 1,2‐dibromo‐3‐chloroproparie (DBCP) in soil after a shallow injection treatment was determined for Yolo fine sandy loam. When injections equivalent to 23.5 litres of DBCP/ha at a depth of 7 to 8 cm were subsequently followed by 15 cm of irrigation water, adequate distribution of DBCP was obtained if the soil was irrigated within 5 days. However, the most rapid and deepest penetration of fumigant was obtained by irrigating 2 to 5 days after application. There was insufficient downward movement of DBCP in non‐irrigated soil.