Limited Irrigation Water Availability Research Articles

The Performance of an Alfalfa–Sainfoin Mixture in the Semiarid Southern High Plains of the USA

While alfalfa (Medicago sativa) is widely used as forage because of its many positive attributes, there are concerns regarding bloat in grazing ruminants, but tannin-containing legumes, such as sainfoin (Onobrychis viciifolia), are non-bloating. Based on interest elsewhere for growing alfalfa–sainfoin mixtures to address bloat concerns, the objectives of a study conducted at Tucumcari, NM, USA, were to compare an alfalfa–sainfoin mixture to the respective monocultures for stand persistence and dry matter yield over three production years in three randomized complete blocks. The onset of drought limited irrigation water availability shortly after the study’s initiation, which limited sainfoin persistence to the second year after seeding. The resulting percentage decline in forage mass in June from year 1 to year 2 was alfalfa > alfalfa–sainfoin > sainfoin. That said, the alfalfa mass was considerably greater than the sainfoin mass, and the June mass of both monocultures was consistent with that in previous studies in the region when fully irrigated (5.57 vs. 2.00 Mg ha−1 for monoculture alfalfa and sainfoin, respectively; p < 0.0004). Alfalfa persistence was greater than that of sainfoin after 3 years. Alfalfa–sainfoin mixtures may have value in the Southern High Plains of the USA and similar semiarid environments when fully irrigated. Additional studies should evaluate mixture seeding ratios and stand performance under fully irrigated conditions with sainfoin reseeding.

A Closed Loop Automated Drip Irrigation System Based on Arduino Uno

In recent years, the limited availability of irrigation water has made the optimal use of water a necessity. Successful irrigation practices in agriculture reduce excessive water usage and increase water use efficiency. Economical use of water can be made possible through modern irrigation systems. Nowadays, automatic control systems in agriculture have made significant progress and offer important advantages. In this study, a mini evaporation pan consisting of nested two cylinders was used (outer cylinder diameter 32 cm, inner cylinder diameter 27 cm, and both with a height of 20 cm) and the water remained at a constant level in both cylinders due to the notch beneath the inner cylinder. A water level sensor was placed inside the inner cylinder, and irrigation was activated based on the signal received from the sensor. The data from the sensor was processed by the microcontroller on the Arduino Uno, and three different irrigation applications were implemented by activating pumps connected to relays at 07:00, 14:00, and 21:00 o’clock, and then the mini-evaporation pan was refilled, and the system waited for the next irrigation period. The automation drip irrigation system maintained irrigation as a closed loop throughout the entire growth period of the lettuce plants using this approach. The addition of a fertilization unit to this system could make it more effective in plant production. The performance of the system will be significantly enhanced by enabling hardware that provides irrigation and fertilization to the plant according to its specific needs in terms of timing and quantity, along with appropriate software integration.

Organic seed priming with curtailed seed rate compensated wheat grains productivity by upgrading anti-oxidant status against terminal drought at flowering and milking

Terminal irrigation drought stress is one of the most drastic abiotic stress to diminish the wheat crop development and grains yield in arid regions of the world. The use of moringa leaf extract (MLE30) via seed priming technique is investigated as an organic and sustainable approach for the mitigation of drought stress along with curtailed seed rate in wheat crop. The study investigated the interaction of organic seed priming: control (dry seeds), hydro-priming, MLE30-priming, seed rate: recommended @ 125 kg ha−1, curtailed @ 25 kg ha−1, and terminal irrigation drought (TID): normal irrigation, mild-TID, severe-TID in wheat crop at agronomic research station, Bahawalpur, Pakistan during the wheat winter season of 2021–2022 and 2022–2023. The application of organic MLE30-priming with curtailed seed rate enhanced antioxidant enzyme activity especially total soluble proteins by 15%, superoxide dismutase by 68%, peroxidase by 16%, catalase by 70%, ascorbic acid by 17% and total protein contents by 91% under severe-TID. Yield and yield-related morphological attributes performed better in MLE30-priming as compared to hydro-priming. An effective trend was observed in the plant's chlorophyll contents, K+, and water use efficiency after being treated with MLE30-priming followed by hydro-priming under curtailed seed rate. The higher benefit–cost ratio and net income return were observed with the application of MLE30-priming with curtailed seed rate under mild-TID and severe-TID. So, it is suggested to adopt the MLE30-priming technique along with a curtailed seed rate for improving the crop establishment, stress regulation, and economic return under limited availability of irrigation water. The project findings recommended that the application of exogenous application of organic MLE30-seed priming favored and compensated the maximum wheat grains production under curtailed seed rate @ 25 kg ha−1 and induced terminal drought stress at flowering and milking conditions.

LAND ALLOCATION PLANNING IN AGRICULTURAL SYSTEMS UNDER UNCERTAINTY: A CHANCE-CONSTRAINED APPROACH IN INEXACT DECISION-MAKING ENVIRONMENTS

This paper explores the application of fuzzy goal programming (FGP) for modeling and solving land allocation problems with chance constraints, aimed at optimizing the production of seasonal crops within agricultural systems in uncertain environments. The decision-making environment in agricultural systems is often characterized by imprecision, particularly due to unpredictable rainfall patterns and limited availability of irrigation water, which are influenced by socio-economic factors. These uncertainties pose significant challenges in real-world agricultural scenarios. The proposed model incorporates fuzzy descriptions for the utilization of cultivable land, farming resources, and the achievement of production goals for seasonal crops. Water supply, as a critical resource, and socio-economic constraints are represented probabilistically within this uncertain decision-making framework. The model addresses land-use planning for the cultivation of five major crops—Paddy, Wheat, Mustard, Potato, and Pulses—across three crop cycles: Pre-Kharif, Kharif, and Rabi, throughout the planning year for the Bardhaman district of West Bengal, India. The solution process focuses on maximizing the membership value (unity) of the fuzzy goals, reflecting the aspirations of the decision maker (DM) as closely as possible, based on their needs and objectives. The potential of this approach is demonstrated through a case study of Bardhaman district, West Bengal, India, illustrating how FGP can be used to address agricultural planning challenges under uncertain conditions.

Is the crop evapotranspiration rate a good surrogate for the recommended irrigation rate?

AbstractNumerous methodologies and technologies of varying levels of sophistication for irrigation rate determination have been developed over the years to address limited irrigation water availability and optimize water productivity. Crop evapotranspiration is currently evaluated mostly according to the FAO56 approach, which has been augmented in recent years with remote sensing of correlated plant indices. When no other information is available, the evapotranspiration rate does give an indication of the optimal irrigation rate in some circumstances. However, in many other circumstances discussed in this short communication, replenishing the soil with crop evapotranspiration either substantially overestimates or underestimates the optimal, physiological (agronomical/economical) irrigation rate. Consequently, this note raises doubts and opens a discussion about the extensive reliance on the evaluated crop (potential or actual) evapotranspiration rate for recommending an optimal irrigation rate (irrigation dose/irrigation amount).

Performance of summer groundnut under different types of plastic mulch

Groundnut is the main kharif crop of the Saurashtra region of Gujarat state. It is also cultivated in summer season in this region. The productivity of summer groundnut is limited by low temperature at initial growth stage, limited availability of irrigation water and higher temperature during reproductive growth period. A field experiment was conducted for two years to evaluate the performance of summer groundnut under six mulch treatments i.e. silver black plastic, transparent LDPE, PP nonwoven, biodegradable, no mulch (raised bed) and flatbed (control). Experiment was laid out with Randomized Block Design (RBD) with four replications. Crop water requirement was calculated by FAO Penman-Monteith method. Irrigation water was applied through drip irrigation in all treatments except flatbed. Silver black plastic mulch resulted in highest plant height, number of pods/plant, weight of pods/plant, pod and haulm yield and minimum weed intensity. Maximum water saving (41.2%), water use efficiency (6.77 kg/ha-mm) and benefit cost ratio (2.85) were obtained from use of silver black plastic mulch.

Effect of irrigation regimes using saline water on faba bean (Vicia faba L.) yield and water productivity in an arid environment*

AbstractA 2‐year study was conducted to assess the effects of irrigation regimes using saline water on soil salinization, yield, water productivity, and net income of faba bean (Vicia faba L.) under actual farming conditions in arid regions of Tunisia. Faba bean (cvs. Luz de Otono and local) was grown on a sandy soil and drip‐irrigated with water having an electrical conductivity of 6 dS m−1. Two deficit irrigation (DI70 and DI40) and one full irrigation (FI) strategy consisting of applications of 40%, 70%, and 100% of crop evapotranspiration (ETc), respectively, were compared to the traditional farmers' irrigation method (FM) in which 16 mm irrigation were applied every 5 days from planting till harvest. Results showed that the lowest soil salinity values at harvest were observed under FI treatment, while the highest were obtained with DI40 and the FM. The maximum values of faba bean yields were obtained under FI and the lowest with the FM. No significant reduction in yields was observed with the DI70 treatment compared to FI, while DI40 and the FM significantly decreased the fresh pod yields. Using 12%–20% more irrigation water than FI treatment, the FM did not improve soil salinity but resulted in a significant yield reduction compared to FI. Total water productivity values varied between 4.9 (FM) and 14 kg m−3 (DI40) across different years and treatments. Compared to the FM, which applies fixed amounts with the same frequency, the FI strategy, which adapts the irrigation amounts to the actual crop water requirements, was more productive and provided a significant advantage in terms of yield and net income. Under limited availability of irrigation water, adoption of the DI70 treatment was found to be a good alternative as it allowed 30% water saving and was subject to limited negative effects on soil salinity, yield, and net income.

The role of ACC deaminase producing bacteria in improving sweet corn (Zea mays L. var saccharata) productivity under limited availability of irrigation water

Accumulation of stress ethylene in plants due to osmotic stress is a major challenge for the achievement of optimum sweet corn crop yield with limited availability of irrigation water. A significant increase in earth’s temperature is also making the conditions more crucial regarding the availability of ample quantity of irrigation water for crops production. Plant growth promoting rhizobacteria (PGPR) can play an imperative role in this regard. Inoculation of rhizobacteria can provide resistance and adaptability to crops against osmotic stress. In addition, these rhizobacteria also have potential to solve future food security issues. That's why the current study was planned to examine the efficacious functioning of Pseudomonas fluorescens strains on yields and physiological characteristics of sweet corn (Zea mays L. var saccharata) under different levels of irrigation. Three irrigation levels i.e., 100% (I100 no stress), 80% (I80), and 60% (I60) were used during sweet corn cultivation. However, there were four rhizobacteria strains i.e., P. fluorescens P1, P. fluorescens P3, P. fluorescens P8, P. fluorescens P14 which were used in the experiment. The results showed that severe water stress (60% of plant water requirement) decreased chlorophyll a, chlorophyll b, and total chlorophyll contents, Fv/Fm ratio and nutrients uptake. A significant increase in F0, Fm, proline, total soluble sugars, catalase (CAT) and peroxidase (POX) activity led to less ear yield and canned seed yield. Combination of four strains significantly increased the yield traits of sweet corn i.e., ear and (44%) and canned seed yield (27%) over control. The highest promoting effect was observed in the combination of four strains treatment and followed by P1 strain in reducing the harmful effects of drought stress and improving sweet corn productivity. However, P14 gave minimum improvement in growth and yield indices under limited availability of water. In conclusion, combination of four strains inoculation is an efficacious approach for the achievement of better yield of sweet corn under osmotic stress.

Effect of Deficit Irrigation on Nitrogen Uptake of Sunflower in the Low Desert Region of California

Nitrogen (N) accounts for more than 80% of the total mineral nutrients absorbed by plants and it is the most widely limiting element for crop production, particularly under water deficit conditions. For a comprehensive understanding of sunflower Helianthus annuus N uptake under deficit irrigation conditions, experimental and numerical simulation studies were conducted for full (100% ETC) and deficit (65% ETC) irrigation practices under the semi-arid conditions of the Imperial Valley, California, USA. Plants were established with overhead sprinkler irrigation before transitioning to subsurface drip irrigation (SDI). Based on pre-plant soil N testing, 39 kg ha−1 of N and 78 kg ha−1 of P were applied as a pre-plant dry fertilizer in the form of monoammonium phosphate (MAP) and an additional application of 33 kg ha−1 of N from urea ammonium nitrate (UAN-32) liquid fertilizer was made during the growing season. Soil samples at 15-cm depth increments to 1.2 m (8 layers, 15 cm each) were collected prior to planting and at three additional time points from two locations each in the full and deficit irrigation treatments. We used HYDRUS/2D for the simulation in this study and the model was calibrated for the soil moisture parameters (θs and θr), the rate constant factors of nitrification (the sensitive parameter) in the liquid and solid states (μw,3, and μs,3). The HYDRUS model predicted cumulative root water uptake fluxes of 533 mm and 337 mm for the 100% ETC and 65% ETC, respectively. The simulated cumulative drainage depths were 23.7 mm and 20.4 mm for the 100% ETC and 65% ETC which represented only 4% and 5% of the applied irrigation water, respectively. The soil wetting profile after SDI irrigation was mostly around emitters for the last four SDI irrigation events, while the maximum values of soil moisture in the top 30 cm of the soil profile were 0.262 cm3 cm−3 and 0.129 cm3 cm−3 for 100% ETC and 65% ETC, respectively. The 16.5 kg ha−1 (NH2)2CO (50% of the total N) that was applied during the growing season was completely hydrolyzed to NH4+ within 7 days of application, while 4.36 mg cm−1 cumulative decay was achieved by the end of the 98-day growing season. We found that 86% of NH4+ (74.25 mg cm−1) was nitrified to NO3− while 14% remained in the top 50 cm of the soil profile. The denitrification and free drainage of NO3− were similar for 100% ETC and 65% ETC, and the maximum nitrate was drained during the sprinkler irrigation period. By the end of the growing season, 30.8 mg cm−1 of nitrate was denitrified to N2 and the reduction of nitrate plant uptake was 17.1% for the deficit irrigation section as compared to the fully irrigated side (19.44 mg cm−1 vs. 16.12 mg cm−1). This reduction in N uptake due to deficit irrigation on sunflower could help farmers conserve resources by reducing the amount of fertilizer required if deficit irrigation practices are implemented due to the limited availability of irrigation water.

The effect of water status on productive and flowering variables in young ‘Arbequina’ olive trees under limited irrigation water availability in a semiarid region of Chile

The intense drought affecting olive production in Northern Chile underscores the need to research non-traditional irrigation strategies to obtain the best crop performance. Accordingly, this study aimed to obtain preliminary data to guide future research on this topic. Different water replenishment levels on crop evapotranspiration (ETc; 13.5, 27.0, 40.5, and 54%) were established in a young orchard, cv. Arbequina, from the end of fruit drop (EFD) to full bloom in the next season. We evaluated the influence of plant water status (Ψstem) and crop load, considered as function of fruit number divided by trunk cross-sectional area, on reproductive and productive variables using multiple linear regressions. Our results show that crop load and Ψstem measured from EFD to harvest affected yield components. Nevertheless, Ψstem had the strongest influence on fruit size, pulp development, oil accumulation, and yield. Oil content and yield were reduced by 54% and 50% for each MPa, respectively, from Ψstem EFD-H − 1.8 MPa, an effect that intensified as crop load increased. During the period of flower development (September–November), the number of flowers per inflorescence and percentage of perfect flowers were reduced when Ψstem was less than − 2.0 MPa. These preliminary results showed that bud differentiation, inflorescence and flower formation are highly sensitive to water deficit.

Optimal cropping pattern design for a major distributary of Hirakud canal command in India

Gravity flow on field to field flooding basis is prevalent in most of the canal command areas in India. Furthermore, the canals being mostly unlined and at many sections ill maintained, enormous conveyance loss of water occurs causing dwindling crop production. Hirakud canal command area located in India is no exception to this predicament. Thus, augmentation of irrigation infrastructures vis-a-vis prudent crop planning is of paramount importance for increasing the overall efficiency of the canal system. This paper describes development of optimal crop planning in the Hirakud command area by considering different objectives of planning (scenarios) so that improvement in irrigation efficiency, in terms of water productivity could be feasible. Among various scenarios, the cropping pattern obtained under Scenario—II, i.e. to utilize the maximum area for cultivation, under the constraint of limiting water availability for each outlet was found to be feasible for optimal land and water utilization and generation of requisite employment. However, keeping in view the affinity of the farmers towards paddy (a heavy duty crop), Scenario—III i.e. to utilize the maximum area for cultivation with the constraints of limited irrigation water availability, and providing irrigation to heavy duty crops for at least one-third of the culturable command area of each outlet, can be adopted.

Effect of Deficit Irrigation on the Growth, Water Use Characteristics and Yield of Cotton in Arid Northwest China

Water shortage is a key constraint to sustainable agricultural production in Xinjiang, Northwest China. To enhance the use efficiency of valuable irrigation water resources, a 2–year experiment (2010–2011) was conducted to quantify the response of cotton (Gossypium hirsutum L.) growth and yield to different degrees of deficit irrigation (DI) regimes; to determine the effects of DI on the characteristics of water use for cotton, seasonal water use, available soil water in the root zone, soil water depletion, evapotranspiration (ET)–based water use efficiency and irrigation–based water use efficiency, and to determine the best DI regime for optimal water–saving and yield output. The plots were irrigated at 100% (100ET), 85% (85ET), 70% (70ET), 55% (55ET) and 45% (45ET) of the regional ET of cotton in northern Xinjiang. The effect of DI irrigation on water use characteristics was evaluated by analyzing available soil water and soil water depletion in the root zone along with water use efficiencies of cotton. The study showed that the growth, water use characteristics and yield of cotton varied with irrigation regime. Seasonal ET and seed cotton yield were linearly correlated with irrigation amount. The second–order polynomial equation best approximated water–yield relationship of cotton in the study area. Cotton yield response factor was 0.65, suggesting limited water conditions were suitable for cotton cultivation. Economic evaluation of DI treatments confirmed that the yield loss was less than 10% under 70ET and 85ET, which was acceptable for greater sustainability. The results suggested that proper DI schemes were necessary for sustainable cotton production in the region. While irrigation at 85ET was safe for high cotton yield, irrigation at 70ET was a viable alternative under limited irrigation water availability.

Potential of Milk Thistle for Biomass Production in Semiarid Regions

ABSTRACTWater shortage is the major constraint for biomass production in semiarid regions. Biomass production of milk thistle [Silybum marianum (L.) Gaertn] and energy balance of this crop under different irrigation regimes (full and deficit irrigation) and soil organic amending treatments (poultry manure [PM] and vermicompost [VC]) was evaluated in a two‐year field experiment. Biomass yield reduced by 10 and 22% under moderate (I75) and severe deficit (I50) irrigation, respectively. Under deficit irrigation, the contribution of leaves and heads to the final biomass reduced in favor of the stalk. Regardless of the irrigation regime, application of soil amendments improved biomass yield. Total energy input used for milk thistle production was 9829 MJ ha−1, in which 68% was related to nonrenewable energy sources. Diesel fuel (51%) had the biggest share of energy used for milk thistle production, followed by irrigation water and machinery. Energy input in I75 and I50 was 7 and 15% less than full irrigation (I100). Net energy obtained from milk thistle was 116,688 MJ ha−1 with energy efficiency (energy output/energy input ratio) of 12.8. Taking into account that milk thistle is an annual crop with low energy input requirements, it seems that milk thistle has a considerable potential for biomass production using I75 in regions with limited irrigation water availability.

Distribution of limited irrigation water based on optimized regulated deficit irrigation and typical metheorological year concepts

Under limited availability of irrigation water during the growing season, farmers must avoid a premature depletion of this resource that may lead to a sizeable decrease in yield. Four levels of net irrigation availability were considered for an onion (Allium cepa L.) crop cultivated in Castilla-La Mancha region (Spain): 1.0 INref (typical net irrigation requirements in the area: 743.3mm); 0.9 INref; 0.8 INref; and 0.7 INref. The available amount of irrigation water was distributed during the growing period by combining the modified optimized regulated deficit irrigation (ORDI) [which determines the actual evapotranspiration (ETa) and maximum evapotranspiration (ETm) ratios (ETa/ETm) per growing stage that maximize yield for a certain amount of irrigation water] and the typical meteorological year (TMY) methodologies. So, optimized irrigation schedules that reach the optimized ETa/ETm ratios per stage and yields were calculated for three TMYs (dry, intermediate, and wet) obtained from a 54-year climatic series (1951–2004). The six months before sowing of each year were analysed to determine if that period was dry, intermediate, or wet. The yield obtained for each level of irrigation availability and the corresponding TMY was considered as the forecasted yield for the current year. Optimized irrigation schedules were corrected during the growing period by replacing the daily climatic data of the TMY by those of the current year. At the end of each growing stage, optimized irrigation schedules were recalculated taking into account the real amount of irrigation water available for the following periods and the forecasted climatic conditions. The effect of this methodology on final yield was simulated by MOPECO (economic optimization model for irrigation water management) during 8 seasons (2005–2012). As a result, onion yields at harvest were approximately 5.1% lower than the forecasted yield at the beginning of the growing period for the different availabilities of irrigation water. As a consequence of premature depletion of irrigation water, only 3 of 24 analysed scenarios reached excessive deficit during the last stage.

Performance of simple irrigation scheduling calendars based on average weather data for annual ryegrass

Poor irrigation management in pastures can lead to yield and quality reduction as well as loss of income through extra pumping and leaching of nitrate fertiliser. A number of irrigation scheduling techniques of varying levels of sophistication have been developed over the years to address limited irrigation water availability and maximise productivity. Despite this, the adoption of irrigation scheduling tools by farmers remains low. The objective of this study was to assess the use of simple irrigation scheduling calendars based on average weather data to improve irrigation management in ryegrass. The calibrated Soil Water Balance (SWB) model was used to generate simple irrigation calendars and assess effectiveness for different scenarios by mechanistically simulating water dynamics and pasture growth. Scheduling irrigation using the calendars gave similar irrigation applications, water losses and yields compared to a more scientific real-time scheduling (in response to soil water depletion by the crop). While site-specific irrigation scheduling calendars can easily be generated by consultants and irrigators, even simpler monthly estimates of average daily water use can also be useful. Application of calendars by farmers is encouraged to improve water and nutrient use efficiency of irrigated pastures, if real-time irrigation scheduling is not employed.

Two Soybean Plant Introductions Display Slow Leaf Wilting and Reduced Yield Loss under Drought

AbstractDue to high costs of irrigation, limited availability of irrigation water in many locations and/or lack of irrigation capabilities, genetic improvement for drought tolerance is an effective method to reduce yield loss in soybean [Glycine max (L.) Merr.]. Slow wilting and minimal yield reduction under drought are important traits in evaluating drought tolerance. Two maturity group III soybean plant introductions (PIs, PI 567690 and PI 567731) and two elite cultivars (DKB38‐52 and Pana) were evaluated with and without irrigation on a sandy soil. Drought was imposed by withholding irrigation at full bloom and continued until moderate wilting was shown by the fast leaf wilting in the check cultivar, Pana. Then, irrigation was resumed until maturity. Genotypes were scored for leaf wilting during the stress period, and yields were assessed at the end of the growing season and used to calculate a drought index. Yields of the exotic PIs were lower than those of the checks under both drought and well‐watered conditions. However, the PIs exhibited significantly lower wilting and less yield loss under drought (higher drought index) than check cultivars. The two PIs may have useful genes to develop drought‐tolerant germplasm and cultivars and maybe useful in genetic and physiological studies to decipher mechanisms responsible for improving yield under limited water availability.

Irrigation water productivity of winter-growing annuals is higher than perennial forages in northern Victoria

The dairy industry in Victoria, Australia, uses more than half the state’s irrigation water, mainly for growing pasture. Information on the comparative water use of forage systems would be useful for dairy farmers aiming to optimise their forage production under conditions of limited water availability. However, there are few data comparing water use under similar management and weather conditions. This paper reports on an experiment which measured and compared the production, water use, and water productivity (forage removed per unit water input) of a range of 6 border-check irrigated forage systems (3 perennial, 2 annual, and a double-cropped) and 1 spray irrigated, annual forage system, used by the dairy industry in northern Victoria. Forage removal was highest from the perennial pastures, lucerne, double-cropped and Persian clover systems in both 2005 and 2006. Irrigation water inputs in 2005 were comparable with average values reported in the literature and were closely related to the length of the growing season, with around 800–850 mm used for the perennial pastures and 340–440 mm used for the border-check irrigated annual pastures. Irrigation water inputs in 2006 were substantially higher than in 2005, reflecting the drought conditions that prevailed throughout most of Victoria, with 1100–1200 mm used for the perennial species and 450–700 mm used by the border-check irrigated annual pastures. These irrigation water requirements highlight considerable year-to-year variation as low-rainfall years are usually high-evaporation years. Irrigation water productivity (WP) was greater for the annual than for the perennial systems. In 2005, irrigation WP was 30–37 kg DM/ha.mm for the annual pastures compared with 21–27 kg DM/ha.mm for the perennial and double-cropped systems. In the drier year of 2006, irrigation WP was higher for the short-season annuals than for the other forage systems. When rainfall, runoff, and changes in soil water content were included in the calculation of total WP, there were no consistent differences in the total WP of the annual and perennial systems in either year. These findings show that under conditions of limited irrigation water availability, farmers will be able to grow more forage using winter-growing annual systems than perennial systems. However, other factors such as nutritive characteristics, cost of production, and cost of transferring feed also need to be considered when deciding which forages to grow.

Overview of the irrigated dairy industry in Australia

The irrigated dairy industry is an important rural industry and confers significant social and economic benefits to Australia. The future prosperity of irrigated dairying will depend on the efficient use of water resources to overcome: (i) limited irrigation water availability, (ii) rising farm production costs, and (iii) the potential negative impacts of irrigation on the environment. This paper overviews the importance of the irrigated dairy industry to Australia, the production system, industry trends and some of the main challenges facing the industry.

Sensitivity analysis of optimal irrigation scheduling using a dynamic programming model

The problem of designing farm irrigation systems is complicated by the fact that the return from a project is a function not only of the design variables, but also of the operation schedules. These operation decisions are not independent, as irrigation applications at any given time period affect the entire set of applications to be made in the future. An optimisation dynamic programming model, CSUDP, was used to analyse the effects of irrigation levels, yield response factors, and initial soil moisture on irrigation scheduling. The CSUDP model requires the following as input data: crop evapotranspiration, rainfall, soil moisture holding capacity, and length of crop sensitivity stages with corresponding yield response factors. Weekly irrigation scheduling, which maximises crop yield, was obtained for a given amount of irrigation water. It has been observed that irrigation scheduling that takes into account crop sensitivity stages reduces irrigation amounts by optimally distributing the irrigation water over the growing season. For some crops, simulation results show that water saving of about 50% resulted in yield reduction of only 25%. By varying yield response factors around the values given in literature, it was observed that increasing the yield response factor of a sensitivity stage decreases relative yield for a given amount of irrigation water. Though residual soil moisture contributed to the crop production under limited irrigation water availability, its effect on irrigation scheduling was found to be limited only to the first 2 sensitivity stages. This information can be of great importance in optimal irrigation water management under limited water conditions.