T. W. Sammis

Computing the crop water production function for onion

Abstract Onions are a major irrigated crop in New Mexico. An excessive amount of water is generally applied, because the crop is shallow-rooted and requires frequent irrigation to achieve good yields. Onions under deficit irrigation have a decrease in evapotranspiration and yield. Consequently, farmers need to use the water production function (wpf) for onions to estimate water requirements at different locations for selected yield goals. The wpf is the relationship between yield and water applied. The same relation can be expressed in terms of evapotranspiration, in which case the production function is known as the evapotranspiration production function (Etpf). A gradient sprinkler line source onion experiment was conducted in 1986 and 1987 at Farmington New Mexico and a linear Etpf determined. The linear Etpf was expressed as a relative Etpf and the yield response factor (Ky), which represents the slope of relative Etpf, was calculated for onions at Farmington, NM and found to be 1.52, compared to 1.5 obtained by [Doorenbos, J., Kassam, A.H., 1986. FAO Irrig. Drain., Paper 33, Rome, Italy] for onions stressed at the yield formation period. A second gradient drip line- source irrigation experiment was conducted at Las Cruces, NM, during 1994–1996 to determine a wpf as related to applied water for drip irrigated onions. The irrigation treatments were 40, 60, 80, 100, and 120% of calculated nonstressed evapotranspiration determined from the sprinkler line source experiment. The wpf was curvilinear because excess water was applied to the different irrigation levels in the experiment in order to keep the base plate of the onions wet so root growth would continue. The result was that part of the applied water went to deep drainage rather than to evapotranspiration. The wpf was corrected for the amount of irrigation water lost as deep drainage and expressed as evapotranspiration versus yield (Etpf) by using reference evapotranspiration measured at Las Cruces and season crop coefficients for selected yield levels measured at Farmington, NM. Maximum onion yield at Las Cruces under the drip irrigation system was 20% higher than measured at Farmington using the sprinkler system. The results indicate that high onion yield are achievable using a drip system compared to a sprinkler system but a larger amount of applied water goes to deep drainage using a drip system compared to a sprinkler system to achieve maximum yield.

A growth-irrigation scheduling model for wastewater use in forest production

Applying wastewater and sludge to land for remediation has been recommended by the Environmental Protection Agency (EPA) as a method to recycle nutrient and organic matter and conserve water resources. The level of sewage treatment can range from simple primary treatment using a lagoon to tertiary treatment using a standard wastewater treatment plant. Small communities are selecting primary treatment and land application as the most cost-effective way of treating municipal wastewater. Wastewater was used to irrigate an Eucalyptus camaldulensis plantation in Ojinaga, Chihuahua, Mexico. The overall objective of the research was to develop a daily growth-irrigation scheduling model (GISM) for Eucalyptus tree plantations based on the trees’ water needs with the source of irrigation water being wastewater from a lagoon sewage treatment system. A second objective was to check this model against measured growth data to determine the limitations of using a simple irrigation-scheduling model to manage the irrigation system to maximize tree growth and wood production. The GISM calculated the evapotranspiration (Et) from the volume balance soil water model and a tree biomass sub-model, based on a water use efficiency (WUE) (biomass/Et) that partitions biomass determined from Et into the component parts of leaves and stems plus branches. The water balance portion of the model computes the Et for grass growing between the trees until a closed canopy system is reached. Weather data and a soil water stress function were used to calculate Et based on calculated reference Et and crop coefficients (Kcs) for both the trees and grass scaled to nonstressed Et. The GISM model accurately modeled height and diameter growth, although, it slightly overestimated the height growth of Eucalyptus for the high irrigation treatment in the second and the third years. The GISM model was successful in predicting height and diameter growth within a 95% confidence level of the measured height and diameter of the trees under all irrigation treatments. Based on the modeled and measured data analysis, the GISM model can be a useful tool to predict tree growth and schedule irrigations for Eucalyptus tree plantations, understand the trees response to environmental and water stress, and to provide better analyses for future research efforts. The climate-driving variables (temperature and rainfall) needed by the model are readily available for any location in the world from the National Climatic Data Center (NCDC).

YIELD-BASED, IRRIGATED ONION CROP COEFFICIENTS

Irrigation scheduling is one of the most important tools for developing best management practices (BMPs) for irrigated projects. Proper irrigation scheduling results in the high irrigation water use efficiencies necessary to conserve limited water resources. Information about crop coefficient (Kc), daily reference evapotranspiration (Eto), and daily evapotranspiration (Et) is important for irrigation scheduling. A gradient sprinkler line source irrigation experiment was conducted to determine the Kc for irrigated onion. The Kc curve obtained from this study corresponds to the typical Kc curve described by Doorenbos and Kassam (1986), with a maximum Kc of 1.09 associated with a maximum yield of 73 000 kg ha –1 , obtained under non-moisture-stress conditions. Growing degree days (GDD) were correlated to the Kc values, which were fitted to a third-order polynomial. The results were integrated to determine the maximum Kc associated with maximum yield. A quartic equation was developed using GDD and relative peak Kc to predict a Kc for a selected yield level. This equation was developed to help onion growers to establish the Kc curve for particular yield. The simulated Kc curve obtained from this method for the non-moisture-stress yield level of 73 000 kg ha –1 was similar to the one measured. This new method is practical and gives farmers an idea of the predicted seasonal irrigation water requirements for their onion crop. In addition, this method is simple and easy to use to schedule irrigation events for onion.

Effect of moisture level on the root pattern of Alfalfa

SummaryThere have been a few investigations on the effect of moisture on root development of alfalfa (Medicago sativa L.), but none have attempted to describe the relationships in a quantitative manner. Therefore, alfalfa root patterns along with yield and evapotranspiration (ET) were examined under different moisture levels, using a line-source sprinkler system. Water application ranged from 28 to 153 cm, the latter representing the potential evapotranspiration. Alfalfa root mass and yield were highest under high moisture levels, and the shoot/root ratio increased with increasing moisture level. The relationships between ET and root mass and between ET and shoot/root ratio were curvilinear. The largest percentage of root mass under all moisture treatments was found in the top 45 cm of the soil profile where the largest differences in total root mass between treatments were observed. The percentages of roots at each soil depth averaged over three ranges of moisture levels were curvilinear functions of soil depth. Although alfalfa roots were found to a depth of at least 150 cm for all moisture levels, there was a greater rooting depth with a higher moisture level. Roots were detected to a depth of 210 cm for the high moisture treatment, although root biomass was small below 170 cm where a sand layer was encountered which may have impeded root penetration. The root diameter was found to be independent of moisture level, which means that there was a greater root surface area with higher moisture levels. Root length density distribution was similar to root mass distribution.

Effects of irrigation method on chile pepper yield and Phytophthora root rot incidence

A field experiment was conducted in 1995 and 1996 to examine the effects of different irrigation methods on yields and Phytophthora root rot disease of chile plants (Capsicum annum New Mexico ‘6‐ 4’). Three irrigation methods, daily drip, 3-day drip, and alternate row furrow irrigation, were applied to plots infested with P. capsici and uninfested plots. For both years, the drip irrigation (either daily or 3day) created higher marketable green chile yields than the alternate row furrow irrigation (p < 0.05), and the yields between the daily and 3-day drip irrigation were statistically similar. The effect of irrigation on marketable combined yields was similar to that on green chile yields. In 1995, root rot disease incidence in the infested plots was significantly higher under alternate row furrow irrigation than for daily and 3day drip irrigation. There was no disease development in the uninfested plots regardless of the irrigation method. The disease decreased green chile yield by 55% (p < 0.1), and combined yield (greena red chile) by 36% (p < 0.1) in 1995 compared to that in uninfested plots in alternate row furrow irrigation. In 1996, however, no disease occurred in any treatment. The results suggested that drip irrigation increases chile yield through providing either favorable soil moisture conditions or unfavorable conditions for Phytophthora propagation. # 1999 Elsevier Science B.V. All rights reserved.

Alfalfa yield as related to transpiration, growth stage and environment

SummaryThe utility of water production models as irrigation management tools is dependent upon their accuracy. Development of precise water production models requires a thorough understanding of how water and other factors interact to affect plant growth and yield. The objective of this experiment was to identify significant environmental variables which control water production function (transpiration vs. yield) variability between harvests and seasons for alfalfa (Medicago sativa L.) over a seven year (1981–1987) period in northwestern New Mexico. A single line-source design was used to supply a continuous gradient of irrigation (I) to the crop, and transpiration (T) was calculated as the difference between evapotranspiration, as estimated by the water balance method, and modeled soil water evaporation at each I level. Yield per cutting was found to be a function of T, growing degree-day accumulation, average daily solar radiation, year and harvest number within year. A multiple regression equation formulated with these variables explained 82% of the yield variability. Average yield per cut in 1981 at 50 mm of T was l Mg ha-1 and in 1985 at the same level of T was 2 Mg ha-1 based on the regression model. Yield per cut at any given level of T, as estimated by the coefficients of this equation reached a maximum at year 5.7 and a minimum in year 1. Within a season, yield per unit T was generally greatest at cut 1 and lowest at cut 2. Total seasonal yield was found to be a function of T and year which explained 90% of yield variability. Yield varied from 0.83 Mg ha-1 to 18.1 Mg ha-1 and T varied from 186 mm to 1298 mm.

SENSITIVITY ANALYSIS OF THE SURFACE ENERGY BALANCE ALGORITHM FOR LAND (SEBAL)

New versions of evapotranspiration (ET) algorithms based on the Surface Energy Balance Algorithm for Land (SEBAL) are being published, each containing slightly different equations to calculate the energy balance. It is difficult to determine what impact changing one or more of the equations or coefficients in the series of equations of SEBAL has on the final calculation of ET. The objective of this article is to conduct a sensitivity analysis of ET estimates in SEBAL to identify the most sensitive variables and equations. A remote sensing ET model based on SEBAL was programmed and validated against eddy-covariance data. A sensitivity analysis was conducted for three contrasting land surface conditions: full, half, and sparse canopy cover in pecan orchards. Results were most sensitive to the selection (according to temperature) of the dry (~zero ET) reference pixel and to c (the estimated ratio of soil heat flux to net solar radiation). At all the three degrees of canopy cover, estimated ET changed by 40% to 270% (1 to 2 mm d-1) when either variable changed from its baseline value by ±50% of the permissible range. Estimated ET was also sensitive to the selection of the wet (full ET) reference pixel and to dT (aerodynamic difference of air and land temperatures). Changes in ET estimates were 47% to 72% (1.3 to 3.7 mm d-1) at both the full and half canopy areas under changes from baseline values equal to 50% of the permissible range for either variable. In addition, ET was sensitive to the roughness length in areas of half canopy cover (ET changed by 61% [1.5 mm d-1]) and to the value of the normalized difference vegetation index (NDVI) in areas of sparse canopy cover (ET changed by 118% [0.35 mm d-1]). Future research on ET algorithm improvement should focus on the above variables and relative equations. The selection of the wet- and dry-spots should be automated to avoid subjective errors from manual selection.

Effects of limited irrigation on lettuce and chinese cabbage yields

SummaryYield response of lettuce (Lactuca sativa L.) and Chinese cabbage (Brassica campestris L. Group pekinensis) to eight different drip irrigation rates was determined in 1980–1984 at Lalamilo, Hawaii. Treatments were arranged in a gradient irrigation design replicated three times and were irrigated daily with amounts ranging from 0.76 mm to 6.09 mm. Yield response from a 0 treatment, equal to rainfall, was also measured. Marketable yield increased linearly with increased water application up to 49.7 Mg/ha for lettuce and 73.1 Mg/ha for Chinese cabbage with an associated seasonal evapotranspiration of 205 mm and 209 mm for lettuce and Chinese cabbage, respectively. The relationship between deficit relative yield (yield divided by maximum yield) and deficit relative evapotranspiration (evapotranspiration divided by maximum evapotranspiration) was linear with a deficit response coefficient of 1.07 for lettuce and 1.35 for Chinese cabbage. Marketable percentage of total potential biomass production decreased linearly with a decrease in marketable yield. Lettuce head size also decreased linearly with a decrease in marketable yield. Water use efficiency (yield divided by water applied) was 24 and 36 kg/m3 of water for lettuce and Chinese cabbage, respectively.

Relationships Between Crop Water Stress Index and Alfalfa Yield and Evapotranspiration

ABSTRACT THE objectives of this study were to compare two methods of determining Crop Water Stress Index (CWSI), and to relate CWSI to the ratio of measured evapotranspiration (E) to potential evaporation (Ep) and to dry forage yield of alfalfa (Medicago sativa L.). The first method requires determination of a lower baseline, the relationship between vapor pressure deficit (V) and canopy minus air temperature (Tc - Ta) when the crop is fully transpiring, and an upper baseline, the relationship between V and Tc - Ta when the crop is non-transpiring. The CWSI is the relative position between the upper and lower baselines. An infrared thermometer was used to measure Tc at 30-min intervals throughout 7 days in 1982 in well-watered alfalfa in Arizona to determine the lower baseline. The highest value of Tc - Ta obtained from alfalfa irrigated using a line-source sprinkler system near Las Cruces, New Mexico was taken to be the upper baseline (4 °C). The infrared thermometer was used to measure Tc on 22 days in 1982 at five locations along the irrigation gradient in New Mexico. The CWSI was then determined for each day at each location on the gradient. Evapotranspiration was calculated for three cutting periods in 1982 using the water balance method at the five locations on the gradient, and Ep was calculated using the Penman equation. Dry forage yield was determined three times at the five locations. Significant relationships (P<0.01) were obtained between CWSI and measured E/Ep (r2 = 0.85), and between CWSI and yield (r2 = 0.79). The second method used energy balance considerations to determine CWSI, and required evaluation of the aerodynamic resistance (ra). Three methods were used to evaluate ra, which gave considerable differences in the CWSI estimates. When ra was evaluated using the wind profile method, CWSI gave a poor estimate of measured E/Ep and yield. This was thought to be caused by the lack of complete soil cover by the alfalfa canopy in this study. However, when ra was evaluated using the convective heat transfer method, the CWSI was significantly correlated (P<0.01) with measured E/Ep (r2 = 0.90). The third method, the leaf boundary layer method, did not provide as good a CWSI estimate as did the second method.

Review of Satellite Remote Sensing Use in Forest Health Studies~!2010-01-27~!2010-04-05~!2010-06-29~!

Satellite remote sensing has been used in forest health management as a method for vegetation mapping, fire fuel mapping, fire risk estimation, fire detection, post-fire severity mapping, insect infestation mapping, and relative water stress monitoring. This paper reviews the use of satellite remote sensing in forest health studies, including current research activities; the satellite sensors, methods, and parameters used; and their accuracy. The review concludes that the Moderate Resolution Imaging Spectroradiometer satellite data (MODIS) are more appropriate for most of the remote sensing applications for forest health than other current satellite data when considering temporal and spatial resolutions, cost, and bands. MODIS has a 1-2 day temporal and a 250-1000 m spatial resolution; the data are free and cover more spectral bands than other satellites (up to 36 bands). We recommend that physical and physiological modeling (e.g., evapotranspiration and biomass growth) be developed for remote sensing of forest health. Some additional satellite sensors, such as for high temperature estimates (as high as 1800 K) and sensors of narrow bands, are also needed.