Marshall English

Perspectives on deficit irrigation

An analysis of deficit irrigation in three quite different situations was conducted to better understand the potential benefits and risks associated with this irrigation strategy. Existing crop yield functions and cost functions, developed independently of the present research, were used to estimate the levels of applied water that would produce maximum net income in each situation. These same functions were also used to estimate the degree to which the three crops could be under-irrigated without reducing income below that which would be earned under full irrigation. The analysis encompassed wheat production in the northwestern USA, cotton production in California and maize production in Zimbabwe. Results suggest that (1) deficits of between 15% and 59% would be economically optimal, depending on the circumstances, and (2) the estimated margin for error in these estimates is quite wide.

Feasibility of soil moisture monitoring with heated fiber optics

Accurate methods are needed to measure changing soil water content from meter to kilometer scales. Laboratory results demonstrate the feasibility of the heat pulse method implemented with fiber optic temperature sensing to obtain accurate distributed measurements of soil water content. A fiber optic cable with an electrically conductive armoring was buried in variably saturated sand and heated via electrical resistance to create thermal pulses monitored by observing the distributed Raman backscatter. A new and simple interpretation of heat data that takes advantage of the characteristics of fiber optic temperature measurements is presented. The accuracy of the soil water content measurements varied approximately linearly with water content. At volumetric moisture content of 0.05 m3/m3 the standard deviation of the readings was 0.001 m3/m3, and at 0.41 m3/m3 volumetric moisture content the standard deviation was 0.046 m3/m3. This uncertainty could be further reduced by averaging several heat pulse interrogations and through use of a higher?performance fiber optic sensing system.

A growth model for coho salmon including effects of varying ration allotments and temperature

Abstract A growth model is developed for coho salmon which accounts for temperatures and feeding rates typically encountered in fish hatchery operation. Feeding rates utilized by the model ranged from maintenance to maximum utilizable rations. The model is derived from an empirical equation for maximum growth rate, and a theoretical equation for net energy utilization. The resultant equation is modified to improve fit at higher feeding levels. Calibration is accomplished with experimentally obtained data. The model is similar to one developed by G.D. Stauffer, but represents an improvement because points on the growth curve between maintenance and maximum ration can be fitted even if maintenance and maximum requirements are obtained independently.

Mapping variability of soil water content and flux across 1-1000 m scales using the Actively Heated Fiber Optic method

The Actively Heated Fiber Optic (AHFO) method is shown to be capable of measuring soil water content several times per hour at 0.25 m spacing along cables of multiple kilometers in length. AHFO is based on distributed temperature sensing (DTS) observation of the heating and cooling of a buried fiber-optic cable resulting from an electrical impulse of energy delivered from the steel cable jacket. The results presented were collected from 750 m of cable buried in three 240 m colocated transects at 30, 60, and 90 cm depths in an agricultural field under center pivot irrigation. The calibration curve relating soil water content to the thermal response of the soil to a heat pulse of 10 W m−1 for 1 min duration was developed in the lab. This calibration was found applicable to the 30 and 60 cm depth cables, while the 90 cm depth cable illustrated the challenges presented by soil heterogeneity for this technique. This method was used to map with high resolution the variability of soil water content and fluxes induced by the nonuniformity of water application at the surface.

Effects of organic matter in aquacultural waste on the ammonium exchange capacity of clinoptilolite

Abstract Clinoptilolite, an ammonium-selective ion exchanger, is being used to control ammonia accumulation in recirculating culture systems. Studies were conducted to establish a correlation among the ammonium exchange capacity of clinoptilolite, level of organic matter in aquacultural wastewater, and regenerant solution type. A recirculating culture system of 2300-I capacity provided wastewater with a represantative organic matrix. Treatment of the wastewater led to a decrease in the performance of clinoptilolite under non-equilibrium (packed-column) and equilibrium operating conditions. The extent of the effects increased with an increase in organic level of the treatment solution. In packed-column tests, the maximum observed reductions in mean removal efficiency (3.5%), volume of wastewater treated prior to reaching breakthrough (14.9%), and operating exchange capacity (19.7%), occurred in columns regenerated with a brine of pH 7.0. Columns regenerated with a brine of pH 10.5 showed little response. Treatment of aquacultural wastewater produced a brown discoloration of the packing which was removed by treatment with 1 bed volume of a hypochlorite restorant solution (0.5% Cl2).

Optimization of feeding schedules in salmon hatcheries

A methodology is developed that determines feeding schedules which will reduce total food consumption for coho salmon in a hatchery during the rearing period. The method presented assumes that the feeding level has a parabolic mathematical form with respect to time. Coefficients of this parabola are converged upon in such a way that the fish achieve a particular size on a chosen release date and simultaneously total food consump tion for the rearing period is minimized. The indicator of feeding level chosen is a nondimensional parameter that equals one at the minimum feeding rate resulting in maximum growth rate and equals zero at a feeding rate that results in a zero growth rate. Results show that for long rearing periods corresponding to rearing in unheated water, the feeding level should be low initially and gradually increase towards the end of the rearing period. Conversely, for rearing periods simulating the accelerated growth periods that occur in heated hatcheries, feeding levels should in general be high at the beginning and gradually decrease throughout the rearing period though sometimes in creasing towards the end. In general, it has been shown that optimum feeding schedules sacrifice efficiency at the beginning of the rearing period when little weight is being gained and max imize efficiency at the end of the rearing period when the greatest amount of weight is being gained. This is in contrast to schedules often devised by hatchery managers to achieve a specified size at a particular date. These schedules may sacrifice efficiency at the end of the rearing period to achieve the goal.

Optimizing Estimates of Soil Moisture for Irrigation Scheduling

Irrigation scheduling commonly involves a water balance analysis in which daily estimates of ET are used to compute cumulative soil water depletion, and occasional soil moisture measurements are used to ‘correct’ the estimate of depletion. However, both ET estimates and soil moisture measurements are characterized by significant uncertainty, and both produce uncertain estimates of depletion. When water use is not limited the problem of uncertainty can be avoided by maintaining soil moisture at higher than critical levels, relying on moisture measurements to decide when to irrigate, and keeping some soil water in reserve as a hedge against uncertainty. On the other hand, deficit irrigation, an increasingly common strategy for maximizing net economic returns to limited water, must be managed differently. Deficit irrigation strategies allow the crop to be stressed to some degree,which implies there will be no soil moisture held in reserve. But errors in management of crop stress can be costly.

A Web-Based Advisory Service for Optimum Irrigation Management

The optimum (profit maximizing) level of irrigation water use is usually less than the yield maximizing level, particularly when water has an associated opportunity cost. However, the amount of analysis required to implement a profit maximizing strategy is usually too time consuming to be practical for most farmers. Furthermore the practical operational constraints imposed on typical irrigation practices are usually too complicated to be fully encapsulated in software. Oregon State University and the NRCS have cooperatively developed a web-based, user-directed application for optimum irrigation management. This system has already completed two years of field trails and has a demonstrated capacity for delivering conventional irrigation schedules. The system is now entering a second phase of development where we are adding new analytical tools that enable easy generation of optimum irrigation schedules. This system, known as Irrigation Management Online (IMO), explicitly analyzes irrigation efficiency and yield reductions for deficit irrigation, performs simultaneous, conjunctive scheduling for all fields in the farm that share a limited water supply, and employs both ET and soil moisture measurements in a Bayesian decision analysis to enhance the accuracy of the irrigation schedules. To mitigate the complexities of irrigation constraints the system has been designed so that the user is an integral part of the irrigation optimization procedure.

A Coordinated Oregon Program for Conserving Energy and Water in Irrigated Agriculture

The Save Water/Save Energy Program developed in Oregon is a cooperative effort designed to assist and motivate irrigators to increase the efficiency of water application and energy use in irrigated agriculture. Entities involved in the cooperative program include local, state and federal resource conservation agencies; electric suppliers; irrigation districts; and individual irrigators. The Save Water/Save Energy Program is designed to take advantage of each energy and water conservation program and is planned to include a program web site, marketing of the program, training for program, and the use of technical coordinators of the energy and water-conservation programs of participating organizations. These coordinators are working to foster communication and education to achieve energy and conservation outcomes.

A Feedback System to Optimize Crop Water Use Estimates in Irrigation Scheduling

This paper deals with errors in estimation of soil water depletion inirrigation management. Such errors can reduce net economic returns to water, increase economic risk and motivate risk averse farm managers to adopt less profitable strategies. Two common methods of estimating depletion are discussed, one based on cumulative ET the other on soil moisture measurements. Both are characterized by significant uncertainty. It is common practice to rely on one or the other of these estimators for irrigation scheduling. This paper proposes an alternative approach that utilizes both estimators in combination. Rather than treating them as deterministic quantities, they are treated as random variables. The probability distributions of each are combined in a Bayesian analysis to derive a probability distribution of depletion, which then provides a better basis for irrigation decisions.