The most common management problem associated with irrigated agriculture is knowing when to apply irrigation and how much of it is required. This is termed irrigation scheduling. Despite numerous techniques and tools developed by the scientific community to aid and improve irrigation scheduling, surveys have shown that farmers growing the same crops in the same region use different amounts of water. This is because of low adoption rates of available irrigation scheduling aids and/or their poor application for various reasons ranging from cost, accessibility and simplicity of the methods. So, as part of a WRC funded project on using Wetting Front Detectors, we seek a simple approach that can be used to better manage irrigation using wetting front detectors (WFD). This prototype WFD was developed in Australia, and was designed to be simple so that it can be understood and used by farmers at any level of training. There are two versions; one is electronic called a FullStop and the other is mechanical, called the Machingilana, a sePedi word for a watchman. The mode of operation of this WFD is based on the physical properties of water movement in the soil or a porous media. The tool give a “Yes” or “No” answer to whether the water has penetrated to a specific depth, and that’s all the farmer needs to know to adjust his irrigation amount of interval according to a chosen algorithm. This experiment on wetting front detectors was undertaken at the University of Pretoria experimental station to: (1) Evaluate two different methods of using electronic wetting front detectors, (II) evaluating two different methods of using mechanical wetting front detectors, and (III) to compare the accuracy of the wetting front detector method against the neutron probe and a computer-based irrigation-scheduling model. Six treatments were evaluated. They were referred to as the Machingilana (MACH), crop factor (CF), FullStop 1 (FSI), FullStop 2 (FS2), neutron probe (NP) and Soil Water Balance model (SWB) treatment. The first four treatments used WFDs in different ways to manage irrigation. Lucerne (Medicago sativa, variety WL 525HQ) was chosen as experimental crop. The NP method was used as control treatment, given the acceptance and credibility this method has received from researchers. The aim was to use dry matter production per volume of water used as an indicator of treatment performance. However, it was later discovered that due to the extensive root system of Lucerne, the crop could compensate for either under- or over-irrigation and dry matter yield was not a good indicator of treatment performance. Statistical analysis of the dry matter yield data collected from three cycles revealed that the treatments were not significantly different at a 5% confidence level, although there was great variation in total amount of irrigation applied to each treatment per growth cycle. This is due to the fact that the crop was able to mine into deeper soil layers for water, although this strategy would not be sustainable in the long run without extra irrigation applied. In the light of this, the trend in soil water deficit obtained with the neutron water meter for each treatment was used to evaluate the six treatments. The four treatments based on WFDs (Machingilana, FS1, FS2 and CF) performed comparatively well to the control and SWB model treatments. However, this is not without discrepancies in all the WFD treatments or the control and SWB model treatment, but the problems associated with each treatment’s successes or failures have been outlined, and with follow-up research, those problems can be rectified. It is concluded that WFDs can be valuable, simple and affordable tools to better manage irrigation, provided appropriate guidelines for using them are applied. / Dissertation (MSc (Agriculture))--University of Pretoria, 2005. / Plant Production and Soil Science / unrestricted

The Mississippi River Valley Alluvial Aquifer (MRVAA) is declining precipitously due to irrigation withdrawal for row-crops. The development of scientific irrigation scheduling techniques and for soybean (Glycine max L.) will reduce withdrawal from the MRVAA. The objective of this research was to determine if soybean grain yield, irrigation water use efficiency (IWUE), and net return above irrigation cost could be optimized using a static irrigation threshold or if the irrigation threshold should be changed as a function of plant growth stage.

5 pp. / This Extension Bulletin is similar to others previously completed for Tucson, Phoenix, Flagstaff, Prescott and Payson. The bulletin provides information on turfgrass consumptive use for the River Cities (Bullhead, Lake Havasu, etc.) and Kingman areas. Consumptive use is provided for each month of the year in units of inches/month and inches/day for three grass production systems: high quality overseeded turf, acceptable quality overseeded turf and acceptable quality turf with no overseeding. The bulletin concludes with a discussion on how to use incorporate this into turf irrigation management programs.

3 pp. / Determining the Amount of Irrigation Water Applied to a Field (AZ1157) / Critical to any irrigation management approach is an accurate estimate of the amount of water applied to a field. Too little water causes unnecessary water stress and can result in yield reductions. Too much water can cause water logging, leaching, and may also result in loss of yield. This publication discusses how to set the water amount and the time period, when taking the system's efficiency into consideration.

3 pp. / Critical to any irrigation management approach is an accurate estimate of the amount of water applied to a field. Too little water causes unnecessary water stress and can result in yield reductions. Too much water can cause water logging, leaching, and may also result in loss of yield. This publication discusses how to set the water amount and the time period, when taking the system's efficiency into consideration.

Revised; Originally Published: 2006 / 3 pp.

A field lysimeter experiment was conducted on a sandy loam soil during the growing seasons of 1989 and 1990. The experiment tested the effects of four water table treatments on soybean (Glycine max) yields. The water table depths were 40, 60, 80, and 100 cm in depth. / Yields were measured in terms of: total seed mass per plant, number of seeds per plant, number of pods per plant, number of seeds per pod, and speed protein content at harvest. / The water management simulation model DRAINMOD, was used to develop irrigation and drainage strategies for soybean production. Three water table management methods were tested with each of three water table depths. The methods were conventional drainage, controlled drainage, and subirrigation, and the water table depths were 40, 60, 80, and 100 cm. / It was shown that for the driest year highest yields are obtained with subsurface irrigation and a weir setting of 40 cm. For the average year, highest yields are obtained with subirrigation and a 60 cm weir setting. For the wet years, best results are found when controlled drainage is used with 80 cm weir setting. It was found that in all but the driest and wettest years controlled drainage improved yields by 10% or more.

Soil Water Balance (SWB), is a generic and mechanistic crop growth model that has been successfully used to model the water balance of several crops. Its ability to combine crop water modelling and irrigation scheduling approaches allows it to be used as a research tool and an irrigation management tool. Since SWB is a tool that could be used as decision making tool for farmers, its accuracy in simulating crop growth, development and soil water balance should be high. To highlight the importance of improved irrigation management for potato crop by the means of a mechanistic soil water balance model and the importance of the photoperiod factor in potato modelling in sub-tropical region, two potato experiments were carried out in two contrasting seasons, namely, spring and autumn. Growth and development responses of potato under both well irrigated and water stressed conditions for spring and autumn plantings were examined. This study successfully quantified the water use and potato growth responses to water stress. The water use efficiency varied with irrigation treatments and planting time, and autumn experiment had generally higher values than spring. Unstressed treatment gave the highest tuber yields irrespective of planting season and marketable tuber yield was higher in autumn than spring. Water stress imposed at tuber initiation until end of tuber bulking was revealed to be the most detrimental to biomass and tuber production. This suggests that water stress at tuber initiation and bulking stage should be avoided if high tuber yield is the target. Growth analysis data were used to determine crop parameters for SWB calibration and validation. The model simulated reasonably well growth, development and soil water balance in both unstressed and stressed conditions. However, simulations results of total and harvestable dry matter towards the end of the exponential tuber bulking stage (50 - 65 DAP) were deteriorated. As a result, the model did not simulate accurately the final yield. This is an indication that the model fails to simulate the size of the canopy and its duration. The time at which tuber initiation commences appeared not be affected by the planting seasons since variation of the duration between emergence and tuber initiation in different seasons was small. This small variation could be attributed to the fact that the potato growing season in South Africa (Pretoria) in spring 2004 and autumn 2005 experiences minimum and maximum temperatures which are acceptable for the growth of potato. In Pretoria, emergence and tuberisation take place under relatively cool temperatures late in September and also early in April when temperatures are relatively cool. Consequently, potato grown in this period may escape the early autumn and late spring high temperatures. However, autumn planting experiences an abrupt change of day lengths from long days to short days towards tuber initiation. This brusque change of day length may change the crop physiology and affect the subsequent normal course of plant growth. If the day length factor could be integrated into SWB, it appears that the model will better simulate potato growth and development. The poor simulation results of total dry matter and harvestable dry matter early in the growing season suggest that the model should be improved by allowing it to simulate the start of tuber initiation. A linear function of average temperature between a base and an optimal temperature corrected with photoperiod factor was found to be the most appropriate method to estimate thermal time required for tuber initiation. This method suggests that the time of tuber initiation can be estimated from its thermal time within two days. / Dissertation (MSc (Soil Science))--University of Pretoria, 2007. / Plant Production and Soil Science / MSc / unrestricted

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3 pp. / Similar Fact Sheets for Payson & Flagstaff / This publication is intended as a brief Fact Sheet that provides estimates of turfgrass consumptive use for Prescott.