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The principles of irrigation and drainage in cracking soils differ markedly from non-cracking soils, and are not thoroughly understood. This paper presents a conceptual model to simulate water and salt flows in cracking soils of the Imperial Valley, CA, in the presence of ground water that contributes partially to ET demand of crops. A salt reactivity function is introduced in the model to account for mineral precipitation (salt deposition) and mineral dissolution (salt pick up). The conceptual water flow model assumes that surface irrigation water moves into the cracks, infiltrates horizontally to wet the soil profile and a fraction bypasses below the root zone into the shallow ground water and is retained for later crop extraction via upflow. Then, water drains vertically through the soil profile step by step, and root water extractions are calculated. When ET exceeds available water upflow of ground water is calculated. Provision for reclamation leaching before the next crop is also made. The associated conceptual salt transport model involves complete mixing of invading and resident soil water. Salt concentration from ET is subjected to a salt reactivity function to obtain salt deposition of calcite and gypsum to obtain salt concentration after precipitation. This reactivity function is also used in the inverse when two or more waters mix to transform salt after precipitation to salt concentration after ET. The flow of salts follows the water transport algorithum. The model has been applied to a point in the Imperial Valley and observed data from Bali et al. () was used for calibration. Simulated point data from four successive years of alfalfa, reclamation leaching, wheat and lettuce are evaluated in this paper. [ABSTRACT FROM AUTHOR]

Production economics literature contains many studies which assume that the producer's goal is to maximize profits. This study tests the hypothesis that Bernoullian and lexicographic utility are more accurate predictors of farmer behavior than profit maximization. Six large California farms were used to test the hypothesis. After-income tax E-V (expectation-variance) boundaries were developed for each farm and utility, and profit maximizing crop plans were determined for each. A goodness-of-fit criterion showed that Bernoullian utility formulations provided the greatest accuracy in predicting actual and planned crop patterns, followed by the lexicographic formulation. Profit maximization showed the poorest predictive power. [ABSTRACT FROM AUTHOR]

Conventional demand based approaches to recreational economics are reviewed and found unsuitable for analyzing the effects of changes of the quality of recreation. An alternative approach using a simulation model is proposed, which allows the use of both quantitative data and subjective input on the qualitative effects. The critical economic variables are found to be fishing recreation visitor days and investment in recreational facilities at the Salton Sea, California. The model results are projected for 20 years and key parameters and assumptions are identified by parametric analysis. These parameters were then subjected to critical interaction by a group of specialists in the area, during a workshop session. Results of the final model are compared to a previous economic study of the region and found to be more pessimistic about the benefits of quality control. Verification of the model is performed by tests of deviation of the predictions of visitor days by the model from the actual visitor days recorded over eight years. [ABSTRACT FROM AUTHOR]

New high-yielding varieties of crops are now available in developing countries. Their potential for improving food and fiber supplies is limited by the availability of inputs such as fertilizer, irrigation, and pesticides. The effects of present, projected, and nonrestrictive supplies of fertilizer are estimated for Punjab State, India. Results indicate that large amounts are needed over and above current plan targets in order to maximize food output and farm incomes. Further, changes in price policy will be necessary to maintain production of crops where no improved-yield-potential varieties are available. Uniform allocations of scarce fertilizer supplies within a state will not maximize agricultural production and incomes. [ABSTRACT FROM AUTHOR]