A center pivot and linear move sprinkler irrigation system are modified to work with low-pressures. Furrow drops which deliver water directly to the furrow and spray heads, which spray the water at approximately 1.20 m above the ground are both tested. Earthen checks are used in the furrow (furrow checks) to retain the water because application rates exceed the infiltration rate of the soil. The stop-and-go movement of the system causes non-uniform water distribution along the furrow. This non-uniformity is investigated in the field and with a computer model. Results indicate that this non-uniformity depends on the furrow check spacing and the length of the system, but not on the system speed. The uniformity perpendicular to the furrows (along the main supply line of the system) is very good. The irrigation efficiency and the yield are high while substantial water and energy savings can be obtained.

The movement of salts in soils following application of feedlot wastes was studied experimentally and theoretically. The objectives of the study were (1) to evaluate the movement of salts in the soil following heavy application of animal wastes as related to the aggregate sizes of manure and water management practices and (2) to develop a mathematical model to predict the movement of salts within the soil and manure mixture. In the experimental study, air dried manure was formed into three distinct sizes, small (to pass 40 mesh sieve), medium (0.9 am in diameter, 1.2 cm in length), and large (1.8 cm in diameter, 1.8 cm in length). Soil columns of 15 cm inside diameter were packed with 30 cm of a soil-manure mixture over a 10 cm depth of soil. The manure application rate was equivalent to 100 metric tons/ha calculated on the basis of the cross-sectional area of the column. A total of five pore volumes of water was passed through the soil under continuous and intermittent water applications. The leachates were collected in 1/2 pore volume increments and the volume, EC, and pH determined immediately. Within 48 hours of the sampling, the leachates were analyzed for Na, K, Ca, Mg, Cl, and five trace elements (Fe, Mn, Zn, Cu, and Ni). The EC of the leachate for the first 1/2 pore volume was significantly (1% level) highest for the small-sized aggregates and the lowest for the large aggregate treatments under both moisture regimes. During the second increment, the order was reversed. In the later water applications, the EC for small aggregates was higher than the other sizes. There were no significant differences between the EC of the leachate from medium and large aggregate treatments during the later periods under either water treatments. Under both moisture regimes, the amount of Na removed from small aggregates decreased more rapidly than the other sizes. More than 90% of the total Na added to the system by manure was removed from the small aggregate treatment. In contrast, the highest amount of K removed (895 mg from small-sized aggregates under continuous leaching' represents about 35% of the total amount present In the manure applied. More Ca was removed from the small-sized aggregate treatments under both moisture regimes than was added by manure application. As for Mg the pattern of the removal was similar to that of Ca. No Cl was detected in the leachate after the fifth 1/2 pore volume was displaced. A mathematical model was developed to predict the movement of readily soluble ions such as Na, K, and Cl from different aggregate sizes of manure. The theoretical curves were compared with earlier experimental data and the parameters appearing in the mathematical equation were estimated. The results for Cl, Na, and K are presented graphically, and the estimated parameters as well as the values of the square roots of the sum of the squares between the theoretical and experimental values as percentage of the sum of the experimental values (SSR) are reported. From the low value of SSR's, it is evident that the model can predict the movement of the readily soluble ions from different aggregate sizes of manure quite accurately. A discussion on the suitability of the model for different sizes of manure aggregates and also a comparison between two different procedures to fit the model to the experimental data are given. In addition, a three phase theoretical model was developed to describe the movement of readily soluble ions from a soil-manure-water system. Experimental data were used in testing the model. The results for Na, K, and Cl are presented graphically. Estimated parameters for the experimental system and the values of SSR are presented. This model also can predict the movement of readily soluble ions from a soil-manure-water system.

The yield, fruiting habits, plant nitrogen uptake, dry matter production, and boll and fiber properties were studied in relation to nitrogen fertilizer and water application rate interactions in trickle-irrigated cotton. Nitrogen applications did not significantly increase yields because of high initial soil nitrogen and nitrogen added with the irrigation water. Significant yield differences did exist between the 60% consumption use (CU) irrigation level and the 90% and 120% CU irrigation levels. The 60% CU level resulted in appreciable plant water stress and appreciably lower yields. Nitrogen additions significantly increased seasonal plant petiole NO₃-N values as well as the number of flowers produced during the growing season. Increased water application rate lengthened the periods of peak flowering and peak boll production but had no effect on petiole NO₃-N. Increased water application rate did not significantly increase boll production, but an increasing trend of increased boll production with increasing water application rates was evident. Nitrogen applications did not significantly increase boll production, but percent boll set for the control treatment was higher. Both nitrogen additions and increased water application rates increased plant nitrogen uptake, which ranged from 163 kg N/ha to 242 kg N/ha for the water levels and 188 kg N/ha to 220 kg N/ha for the nitrogen treatments. Increased water application rates significantly increased dry matter production during the growing season. Nitrogen and water application rates affected only a few boll and fiber properties. Average boll size was increased significantly with increasing water application rates. This partially accounted for the higher yield observed at the higher irrigation levels.

Levels of nitrogen, phosphorus, potassium, calcium, magnesium, zinc, manganese, copper and selenium in grasses grown under rainfed conditions on different soils in the Santa Rita Experimental Range and other areas in southern Arizona were evaluated to determine whether these nutrients are deficient, sufficient or toxic to cattle. In the greenhouse, two grasses grown on five different soils representing four soil orders were fertilized with nitrogen and phosphorus and the uptake of a number of nutrients was determined. For the grasses collected from the field, the nutrient contents generally decreased with time to maturity and the highest levels were attained during August when the grasses were young, and March, the start of the spring growth. The nitrogen and phosphorus contents were lower than the requirement for grazing cattle indicating the need for supplementing protein and phosphorus. The contents of potassium, calcium, zinc, manganese, copper and selenium were adequate for grazing animals. Although the magnesium level in some cases was lower than the requirement, it was considered adequate because its deficiency is now known in warm season grasses. The nutrient contents in the grasses grown on Comoro soils were generally higher than when grown on an adjacent Sonoita soil. Soil analysis revealed no consistent pattern of the levels in these grasses and in Comoro and Sonita soils on which they were grown, except for nitrogen. The nutrient contents in the heads and leaves of two species of grasses were higher than in their stems. The greenhouse experiments showed that the vegetation on the N + P treatment was more vigorous than on the nitrogen treatment and the control, respectively. For the two grasses grown on the five different soils, the nitrogen and magnesium contents mostly were not significantly different between the three treatments, probably due to the dilution effect resulting from the vigorous vegetative growth on the N + P treatment. The phosphorus content in the grasses grown on the N + P treatment was significantly higher than the other two treatments. The nitrogen and phosphorus levels in the soils before and after planting were similar indicating that nitrogen and phosphorus fertilization helped maintain their levels in the soils. Other nutrients in the soils decreased after planting. Most of the nutrients were higher in the surface soils than in the subsurface soils, probably due to the ability of grasses to recycle nutrients from the subsoil.

Spectral and surface temperature measurements were made of various rangeland surface conditions using a hand-held radiometer and an infrared thermometer. Three different soil series, each with three plots with varying surface conditions were studied. T-tests, simple-linear regression analysis, and principal components analysis were used to relate rangeland surface features to spectral and thermal measurements. Vegetation was the feature that had the most effect on surface temperature under dry conditions, and vegetated plots had a lower percent change in daily temperature than bare plots. Under wet conditions, there were no significant differences in temperature between plots with differing surface conditions. Correlation coefficients showed that the hue of the soil was highly correlated with the percent reflectance in all four spectral bands, and the green grass cover decreased the reflectance in bands one, two and three. There were high correlation levels among the spectral bands showing an overlap of spectral information.

The purpose of this investigation was to develop empirical relationships between pan evaporation and meteorological factors, under varied climatic conditions. Linear regression equations relating potential evapotranspiration and pan evaporation were derived for five stations in Arizona from January to December, 1983. Five climatological models (temperature, temperature-radiation, net radiation, solar radiation, and Penman combination) were applied to data collected from Mesa, Tucson (Campus Agricultural Center and UA 1), Oracle Agricultural Center, and Yuma. At each site high correlations were found between predicted values and open pan evaporation when data were grouped into monthly and weekly periods, although coefficients of variation were markedly different. Of the five methods, the net radiation equation, which required local calibration showed the poorest agreement between the empirical and measured values. Improvement in comparisons between empirical and measured values was observed with the temperature, radiation-temperature, and solar radiation methods. The Penman combination equation corresponded most closely to measured values.