Allen G. Smajstrla

Water Requirements and Crop Coefficients of Drip-irrigated Strawberry Plants

Studies were conducted for three production seasons between 1988 and 1991 to measure water use of drip- irrigated strawberry plants and to evaluate the effects of soil tension management level on fruit yield and drip irrigation water requirement. Water balance lysimeters were designed and installed to measure monthly water requirements of drip- irrigated strawberry plants. Drip-irrigated strawberry plots that were established next to the lysimeter facility used tensiometers to schedule irrigations with treatment management levels of 5, 10, and 15 kPa of soil tension.

Evapotranspiration and crop coefficients for young blueberries in Florida

A three-year study of water use by two species of cultivated blueberry was conducted. The experiment was performed on two rabbiteye (Vaccinium ashei Reade) varieties, Premier and Powderblue, and one highbush (Vaccinium corymbosum L.) variety, Sharpblue. Water was applied to the plants using a microirrigation system. Irrigations were triggered at three soil water tension levels: 10-kPa, 15-kPa, and 20-kPa. Water use for both species was monitored using drainage-type lysimeters and a water budget method. Grass reference crop modified coefficients for the modified Penman equation (Burman, 1980) during the first three years of establishment were developed based on the 10-kPa treatments for both species. Modified crop coefficients for microirrigated highbush blueberries were below 0.2 during the first two years of plant establishment and increased to 0.35 in the third year as the plants rapidly increased in size. Coefficients for the rabbiteye varieties were consistently higher during all three years, reaching 0.5 in the third year.

Microcomputer-based control of irrigation systems

A low cost, computer-based irrigation control system is presented. The system uses readily available components that result in a reliable and highly flexible controller. The system has been used in a variety of field conditions including mist, sprinkler, and microirrigation systems. Commercial installations have successfully used this system for a period of up to six years. This article presents the components of a successful microcomputer-based control system for irrigation management.

Parametric Uncertainty in Stochastic Precipitation Models: Wet Day Amounts

A methodology was developed to quantify the uncertainty associated with maximum likelihood parameter estimates used in the wet day amount component of stochastic rainfall models. Traditional point parameter estimates were combined with interval estimates to construct a probabilistic region of parametric uncertainty. Regions of model uncertainty were then constructed from the region of parametric uncertainty. The wet day amount model was implemented by repeatedly selecting parameters from a bivariate normal distribution. The results of this test suggested that the amount model was sensitive to small changes in parameters. The model was least sensitive to parametric uncertainty for small wet day amounts and increased in sensitivity toward large amounts.

LONG-TERM VARIABILITY OF MONTHLY TOTAL PRECIPITATION

A methodology was developed to quantify long-term temporal variability of monthly total precipitation. Ninety-three years of data from four weather stations on the Florida peninsula were used. This peninsula, covered by a single 8° × 10° grid of the NASA/GISS atmospheric GCM, is a transitional climatological region, influenced on a seasonal basis by mid-latitude continental fronts, convective thunderstorms and tropical disturbances. Traditional statistical descriptors suggested that the distribution of monthly total precipitation was highly non-Gaussian. A gamma probability density function was successfully fit to the historical data and used to investigate the possible presence of long-term trends. These findings suggested that the distribution of monthly total precipitation, rather than the mean and standard deviation, should be used in weather and climate model development and validation. This methodology also may be applicable to sub-grid scale spatial variability of monthly precipitation.

Evaluation of a computer model to simulate water table response to subirrigation

(3) and Salvadore Jose Locascio(4) Abstract - The objective of this work was to evaluate the water flow computer model, WATABLE, using experimental field observations on water table management plots from a site located near Hastings, FL, USA. The experimental field had scale drainage systems with provisions for subirrigation with buried microirrigation and conventional seepage irrigation systems. Potato (Solanum tuberosum L.) growing seasons from years 1996 and 1997 were used to simulate the hydrology of the area. Water table levels, precipitation, irrigation and runoff volumes were continuously monitored. The model simulated the water movement from a buried microirrigation line source and the response of the water table to irrigation, precipitation, evapotranspiration, and deep percolation. The model was calibrated and verified by comparing simulated results with experimental field observations. The model performed very well in simulating seasonal runoff, irrigation volumes, and water table levels during crop growth. The two-dimensional model can be used to investigate different irrigation strategies involving water table management control. Applications of the model include optimization of the water table depth for each growth stage, and duration, frequency, and rate of irrigation.