Centre Pivots Research Articles

Comparison of single vs composite soil electrical apparent conductivity-directed samples of irrigated soils for inorganic nitrogen estimation with electromagnetic induction sensors

The management of soil can be improved by precision agriculture. A way to achieve this is by quantifying NH4+–N and NO3−–N in soil. The sampling of soil for quantifying these N species is a laborious task. Electromagnetic induction (EMI) sensors could ease the task, providing a large quantity of data. The correlation of inorganic N with soil electrical apparent conductivity (ECa) in either single or composite samples is essential to accomplish this. Using an ECa-directed sampling approach, suitable sampling points were identified at four centre pivots. Single and composite samples were collected in 300 mm increments to 600 mm at Hofmeyr and 1500 mm at Douglas, Luckhoff and Empangeni. The samples were analysed for NH4+–N and NO3−–N from which total inorganic N (TIN) was calculated. All three inorganic N fractions were correlated insignificantly to in-field readings of ECa, implicating that EMI sensors are not suitable for inorganic N estimations in these irrigated soils. A comparison between single and composite samples, however, showed a good agreement of NH4+–N concentrations which was not true for NO3−–N or TIN concentrations. Composite samples are recommended for inorganic N measurements with an EMI sensor. Single samples could be used when only NH4+–N is analysed.

First evidence of widespread, severe soil erosion underneath centre-pivot irrigation systems

Centre-pivot systems are widely used for irrigation in agriculture. However, excessive water application rates under low pressure centre-pivot systems can lead to soil erosion, which degrades soil structure and increases crop vulnerability to droughts. Although efforts have been deployed to measure soil erosion underneath individual centre pivots, a large-scale systematic assessment of extent and severity of soil erosion in centre-pivot irrigated fields is currently lacking. Here we used Google Earth™ satellite images to provide first evidence of widespread, severe soil erosion in centre-pivot irrigated agricultural land. We focused on the municipality of Cristalina (6154 km2), in the Brazilian Central Highlands, where centre pivots irrigate approximately 60,000 ha of cropland. The study area is in the Cerrado biome, which is one of the most important grain-producing regions in the world and Brazil's main centre-pivot irrigation area. By mapping erosion features under centre pivots, we found that 29 % of centre-pivot fields displayed signs of rill erosion, with individual rills up to a length of 1200 m. Most erosion features were identified during the dry season of the Brazilian Cerrado, which coincided with the period of greater satellite-image availability. Moreover, we found that compacted centre-pivot-wheel tracks often triggered rill incision and that eroding centre-pivot fields displayed higher slope gradients and were better connected to surface waters than the non-eroding fields. Ultimately, the frequent identification of severe erosion features in the centre-pivot fields during the dry season indicates that irrigation causes and/or aggravates soil erosion in Cristalina and likely in other parts of the Brazilian Cerrado. This first systematic evidence of widespread soil erosion underneath centre-pivot systems highlights that irrigation erosion is an important but neglected driver of land degradation, and that urgent action is required to protect affected soils for future generations.

Corrosion caused by fertigation with urea and potassium chloride solutions resembles that generated by irrigation

AbstractCorrosion is a common problem in irrigation systems consisting of metal parts. Fertigation can aggravate this phenomenon because fertilizers, once dissolved in water, usually tend to be corrosive. In this study, the effects of corrosion resulting from fertigation with solutions of white potassium chloride (10 g L−1) and urea (10 g L−1) on galvanized steel and AISI 304 stainless steel specimens, materials similar to the centre pivots and injection pumps, were evaluated by simulation tests. During the experiment, the mass loss, corrosion penetration rate, thickness loss and estimated useful life of the specimens were calculated. The results showed that the variation in the fertilizer source as well as the type of metal influenced the corrosion effects. Furthermore, the useful life expectancy of steels intended for irrigation in systems that practice fertigation practically does not differ from the systems where only irrigation is practiced. The corrosion resistance of stainless steel is significantly higher than that of galvanized steel, so its use should be considered in irrigation systems. In addition, it is interesting that the Zn coating on the galvanized steel pipes used for irrigation presents at least twice the thickness to ensure greater protection of the steel substrate.

Metabolic power in the men’s European handball championship 2020

ABSTRACT Purpose To ascertain the typical metabolic power characteristics of elite handball players of different positions, and whether changes occur within matches. Methods 414 elite male handball players were included. During all 65 matches of the EURO 2020, local positioning system data were collected, yielding 1853 datasets. Field players were categorised into six positional groups: centre backs (CB), left/right wings (LW/RW), left/right backs (LB/RB) and pivots (P). Metabolic power, total energy expenditure, high-power energy, and the equivalent distance index were calculated. We used linear mixed models with players as random and positions as fixed effects models. Intensity models adjusted for time-dependency by incorporating the duration of play. Results LW/RW spent most time on the court, expanded most total energy, and most relative energy per kg body weight in the high-intensity categories. CB played at the highest mean metabolic power (7.85 W/kg; CI95% [7.67, 8.03]). Playing intensity decreased by 2.5% (0.2 kJ/kg/s; CI95% [0.17, 0.23]) per 10 min played. Conclusion Positional differences in metabolic power parameters exist. In general, wing players had the highest volume and CB the highest intensity of match-play. Analysis of metabolic intensity in handball should take position and players’ time on the court into account.

Shared centre pivot. An experience of smallholder irrigation in Midwest Brazil

Irrigation enables crop intensification and improves the smallholder’s household livelihood. Centre pivot irrigation, a system predominantly used in medium to large individual farms, has recently been promoted for smallholder collective irrigation in developing countries. The objective of this research was to assess the irrigation performance and evolution of shared centre pivot systems at the Itamarati Rural Settlement in the Midwest of Brazil, where around 1000 smallholders were organized in small groups between 2001 and 2004, to farm 85 centre pivots collectively. Quantitative and qualitative data were collected in a mixed-approach, and used to characterize the evolution and sustainability of the centre pivots shared. We collected information from published and unpublished reports, and we conducted our own surveys, interviewing twenty-five farm groups and forming focus groups in a 3-year phased process. Irrigation intensity (the ratio of irrigated area over the area equipped for irrigation) declined sharply from 0.75 in 2004/2005–0.12 in 2020. The immediate pressures triggering the abandonment process were: the farmers’ insufficient technical capability, low productivity of the irrigated crops, and high operational and maintenance costs. At the root of these drivers was the incapacity to exert the collective action required by the highly centralized shared centre pivot system. The progressive giving up of collective management and the concentration of land in larger farms seems to be inexorable. The Itamarati experience was a paradigm of a top-down project whose lessons are important for policymakers. We concluded that centralized collective systems are unsustainable unless the community that adopts them has a high sense of union and a capacity for collective action.

Towards improving the global water application uniformity of centre pivots through lateral speed adjustment

An initial step is made towards improving the global water application uniformity of centre pivots by adjusting the lateral speed based on diurnal changes of wind drift and evaporation losses (WDEL). A large WDEL dataset was used to construct an artificial neural network (ANN) model capable of predicting the above ground application efficiency (AGAE ≈ 1- WDEL) from input weather data. Given its reasonably good accuracy (RMSE = 1.5%), the ANN model was then applied in heuristic, simple and dynamic algorithms that used forecasted or real-time weather parameters corresponding to the hourly time intervals of the pivot's revolution time. For each timing interval, the final output of the algorithms is a coefficient ( λ ), that when multiplied by the lateral speed, can ensure a more consistent water delivery depth across the field. The proposed algorithms were theoretically tested for extremely hot, dry, humid, and windy days. These efforts indicated that under the climatic conditions of the study, λ could potentially vary between 0.92% and 1.06% if the revolution time is about 24 h. The λ coefficient typically increased from 1:00 AM to 9:00 AM, then decreased until the sunset, between 19:00 to 21:00, and then increased again until midnight. This general trend for λ could however, be disrupted by sudden changes in the wind speed. Future studies should conduct extensive field work to test the efficacy of the proposed algorithms and quantify the improvement of centre pivot global water application uniformity through the lateral speed adjustment. • Centre pivot lateral speed can be adjusted to account for a changing application efficiency. • Two theoretical algorithms were developed to improve the global water application uniformity. • The first algorithm uses forecasted weather data while the second uses real time data. • The lateral speed adjustment factor varied within ±6% during a 24-hr cycle. • Centre pivot lateral speed adjustment is easy to implement.

Optimal Operation of Farm Turbine Pumps.(Dept.C)

One of the costiest items in agriculture is the cost of providing water. The purpose of this investigation is to operate the turbine pumps to cope with the irrigation water and pressure requirements for the existing system of irrigation. It is also desired to maintain a constant pump discharge for different static water levels by varying the pump speed to adjust an increase or decrease in water discharge. The study was carried out on two turbine pumps at the College Research Station, each of which has fourteen stages; these pumps are supposed to irrigate the College Farm including two centre pivots. The system head curves were constructed, points of intersection with the pump characteristic curves at different pump speeds, are the operating points, which could be used to give the required discharge and pressure at a specified pump speed according to the given tables for the gross irrigation water requirements. Equations of system head curves and pump characteristic curves are presented, from which the operating points could be obtained.

Irrigation uniformity under different socio‐economic conditions: evaluation of centre pivots in Aragon (Spain) and Utah (USA)

AbstractThis study is an analysis of the influence that the socio‐economic context may have on irrigation performance. The main objective is to provide useful information to support the decision‐making processes of farmers, water user associations, policy‐makers and agritech companies. For this purpose, 34 centre pivots were evaluated in Aragon (Spain) and Utah (USA). Utah has a lower agricultural production potential than Aragon, and crop production is a secondary activity with respect to livestock production on many farms. In Aragon, farms are mainly devoted to crop production. These and other features may bias farmers' decisions regarding investment, operation and maintenance of their irrigation systems. This bias may be the underlying cause of the lower irrigation uniformity obtained in Utah. Coefficients of uniformity (CU) averaged 90% in Aragon and 80% in Utah. The gap between the actual and potential (90%) CU translates into an estimated net land productivity reduction of −18% (€66 ha−1, US$89 ha−1) in Utah. Measures aimed at closing this gap could cost less than €15 ha−1 (US$20 ha−1). Multidisciplinary approaches are required to quantify these gaps and to understand their causes in order to bridge them in a cost‐effective manner. Copyright © 2016 John Wiley & Sons, Ltd.

Uniformity Assessment of Irrigation with Centre Pivots in Uruguay

Irrigation with centre pivots has increased exponentially under the last decade in Uruguay; starting with a few sets, now there are more than 350 sets which cover 30.000 ha. To conduct performance evaluations of the centre pivots we selected a representative sample of the sets used in Uruguay: 20 sets in three different regions in the country, whose lateral longitude ranged from 398 to 802 m. Uniformity tests of the equipments were conducted according to the methodology proposed by the international standards: ANSI/ASAE S436.1 (JUN 1996). The uniformity coefficient of Hermann and Hein (CUh) of 16 sets reached acceptable values (80 to 87 %), while the rest obtained very low coefficient values (54 to 71%). Distribution Uniformity values (UD) followed the same tendency as CUh values. The 16 sets with high CUh, obtained high UD values (71 to 85%), whereas the rest got lower UD values (26 to 70%). Centre pivots may attain high application uniformity in Uruguayan agrosystems, given an adequate combination of system design and operation. An inaccurate management of centre pivots due to operation below required pressures and to poor maintenance of sprinklers will directly impact the sheets applied, and the application uniformity and efficiency of the centre pivot system.

Optimal reservoir capacity for centre pivot irrigation water supply: Maize cultivation in Spain

Centre pivots are one of the most widespread irrigation systems in the world. The aim was to develop a tool to optimise the design and management of the water distribution and centre pivot systems seeking to minimise water application cost per unit area (CT), including investment (Ca), operation (Ce), and maintenance costs. With this aim, two options were considered: to feed the centre pivot 1) directly from an aquifer or 2) using a regulation reservoir. A software tool DEPIRE (design of centre pivot with regulating reservoir), was developed and implemented in MATLAB 2012b (The MathWorks Inc., Natick, MA, USA). It determines optimal flows, pipe diameters, pumps power and the volume of the regulation reservoir for any crop water requirement, different electricity rates and water availability in the tube well. With this tool, the effect of the irrigated area (S), dynamic water level (DWL) in the aquifer and the pumping flow rate on the CT was evaluated for a maize crop in Spain. The study area representing the minor CT was 70 ha for direct pumping from the borehole and 100 ha when using an intermediate reservoir. Incorporating a regulation reservoir generates lower CT than direct feed from the borehole for S > 100 ha for any DWL. CT increased linearly with the DWL due to a significant increase in Ce which primarily affects the cost of water extraction from the aquifer, with a smaller effect on the application cost of the irrigation system.

Uniformity Assessment of Irrigation with Centre Pivots in Uruguay

Irrigation with centre pivots has increased exponentially under the last decade in Uruguay; starting with a few sets, now there are more than 350 sets which cover 30.000 ha. To conduct performance evaluations of the centre pivots we selected a representative sample of the sets used in Uruguay: 20 sets in three different regions in the country, whose lateral longitude ranged from 398 to 802 m. Uniformity tests of the equipments were conducted according to the methodology proposed by the international standards: ANSI/ASAE S436.1 (JUN 1996). The uniformity coefficient of Hermann and Hein (CUh) of 16 sets reached acceptable values (80 to 87 %), while the rest obtained very low coefficient values (54 to 71%). Distribution Uniformity values (UD) followed the same tendency as CUh values. The 16 sets with high CUh, obtained high UD values (71 to 85%), whereas the rest got lower UD values (26 to 70%). Centre pivots may attain high application uniformity in Uruguayan agrosystems, given an adequate combination of system design and operation. An inaccurate management of centre pivots due to operation below required pressures and to poor maintenance of sprinklers will directly impact the sheets applied, and the application uniformity and efficiency of the centre pivot system.

Effect of Pethoxamid (TKC-94) Rate and Application Time on Weed Control and Phytotoxicity in Flue-cured Tobacco

Due to the risk of weed resistance to herbicide control, there is continuous need for new chemicals to be tested for control of weeds. Such work is of major importance as herbicides form a vital line of defence against weeds which would otherwise cause yield loses of even up to 100%. In this work, the herbicide pethoxamid (TKC-94) was evaluated to establish the time and rate of application that would give efficacious weed control without causing phytotoxicity. In the first year, the herbicide was included in a simple screening trial comprising twelve herbicides arranged in a randomised complete block design. After it had stood out it was selected for further development. In the second year, in a split plot design with four blocks and six treatments, it was applied as TKC-94 at 1.88 kg a.i /ha applied just after holing out (a.h.o.) and TKC-94 at 1.88 kg a.i. /ha applied immediately after planting (i.a.p.). Three controls, Dual 960 ec (Generic, a.i. s-metolachlor) at 2.2 kg a.i. /ha i.a.p and Dual Magnum (original formulation, a.i. smetolachlor) at 2.2 kg a.i. /ha i.a.p as checks and an untreated control were included. This trial showed that applied a.h.o., TKC-94 was phytotoxic, stunted Tobacco and reduced yield and weed efficacy while the i.a.p. was ideal and showed no phytotoxicity and had good weed efficacy. In the third year, the i.a.p. time of application was tested in a similar design but now, more rates of TKC-94 were tested. The rates were, TKC-94 at 0.0 kg a.i. /ha i.a.p, TKC-94 at 1.88 kg a.i. /ha i.a.p., TKC-94 at 2.82 kg a.i. /ha i.a.p., and TKC-94 at 3.76 kg a.i. /ha i.a.p. Dual Magnum at 2.2 kg a.i. /ha i.a.p was included as a check. This work confirmed the potential of the herbicide as a broad spectrum material and showed that the best rate that would ensure broad spectrum control was 2.82 kg a.i. /ha. Further research could look at application of this material in irrigation water in order to cater for those farmers with centre pivots. In addition, the early post emergence control of weeds may also need to be researched in order to give the farmer more flexibility in using this herbicide.

Effect of Time and Rate of Application of Bateleur Gold (S-Metolachlor + Flumetsulam) on Phytotoxicity and Weed Control Efficacy in Flue-cured Tobacco

Herbicides are usually the first line of defence against weeds and form a formidable pair with mechanical control whether with machinery of hand hoeing. Due to the risk of weed resistance to herbicide control and environmental contamination, there is continuous need for new chemicals to be tested for control of weeds. In this work, the herbicide Bateleur Gold, a factory premix of s-metolachlor and flumetsulam was evaluated to establish the time and rate of application that would give efficacious weed control without causing phytotoxicity. In the first year, the herbicide was included in a screening trial comprising twelve herbicides arranged in a randomised complete block design. After good efficacy when applied immediately after planting, it was selected for further development. In the second year, in a split plot design with four blocks and four treatments, it was applied at 0.455 kg a.i ha -1 applied just after holing out (a.h.o) and at the same rate immediately after planting (i.a.p). A positive control Dual Magnum (smetolachlor) at 2.2 kg a.i.ha -1 i.a.p was used as a check and an untreated control was included. This trial showed that applied a.h.o, Bateleur Gold neither stunted Tobacco nor reduced yield but somewhat reduced weed efficacy especially overall (total weeds) nor grasses while the i.a.p. was ideal and showed no phytotoxicity and had good weed efficacy. In the third year, the i.a.p time of application was tested in a similar design but now more rates of Bateleur Gold were tested. The rates were, Bateleur Gold at 0.455, 0.92, 1.365 and 1.82 kg a.i.ha -1 . Dual Magnum at 2.2 kg a.i.ha -1 i.a.p was again included as a check. This work confirmed the potential of the herbicide as a broad spectrum material and showed that the best rate that would ensure broad spectrum control was 0.92 kg a.i.ha-1. Further research could look at application of this material in irrigation water in order to cater for those farmers with centre pivots. In addition, although application a.h.o. does not cause stunting of Tobacco; more work may be needed to show this with greater confidence.

Water-use efficiency and productivity trends in Australian irrigated cotton: a review

The aim of this review is to report changes in irrigated cotton water use from research projects and on-farm practice-change programs in Australia, in relation to both plant-based and irrigation engineering disciplines. At least 80% of the Australian cotton-growing area is irrigated using gravity surface-irrigation systems. This review found that, over 23 years, cotton crops utilise 6–7 ML/ha of irrigation water, depending on the amount of seasonal rain received. The seasonal evapotranspiration of surface-irrigated crops averaged 729 mm over this period. Over the past decade, water-use productivity by Australian cotton growers has improved by 40%. This has been achieved by both yield increases and more efficient water-management systems. The whole-farm irrigation efficiency index improved from 57% to 70%, and the crop water use index is >3 kg/mm.ha, high by international standards. Yield increases over the last decade can be attributed to plant-breeding advances, the adoption of genetically modified varieties, and improved crop management. Also, there has been increased use of irrigation scheduling tools and furrow-irrigation system optimisation evaluations. This has reduced in-field deep-drainage losses. The largest loss component of the farm water balance on cotton farms is evaporation from on-farm water storages. Some farmers are changing to alternative systems such as centre pivots and lateral-move machines, and increasing numbers of these alternatives are expected. These systems can achieve considerable labour and water savings, but have significantly higher energy costs associated with water pumping and machine operation. The optimisation of interactions between water, soils, labour, carbon emissions and energy efficiency requires more research and on-farm evaluations. Standardisation of water-use efficiency measures and improved water measurement techniques for surface irrigation are important research outcomes to enable valid irrigation benchmarks to be established and compared. Water-use performance is highly variable between cotton farmers and farming fields and across regions. Therefore, site-specific measurement is important. The range in the presented datasets indicates potential for further improvement in water-use efficiency and productivity on Australian cotton farms.

THE WATER RELATIONS AND IRRIGATION REQUIREMENTS OF SUGAR CANE (SACCHARUM OFFICINARUM): A REVIEW

SUMMARYThe results of research on the water relations and irrigation needs of sugar cane are collated and summarized in an attempt to link fundamental studies on crop physiology to irrigation practices. Background information on the centres of production of sugar cane is followed by reviews of (1) crop development, including roots; (2) plant water relations; (3) crop water requirements; (4) water productivity; (5) irrigation systems and (6) irrigation scheduling. The majority of the recent research published in the international literature has been conducted in Australia and southern Africa. Leaf/stem extension is a more sensitive indicator of the onset of water stress than stomatal conductance or photosynthesis. Possible mechanisms by which cultivars differ in their responses to drought have been described. Roots extend in depth at rates of 5–18 mm d−1 reaching maximum depths of > 4 m in ca. 300 d providing there are no physical restrictions. The Penman-Monteith equation and the USWB Class A pan both give good estimates of reference crop evapotranspiration (ETo). The corresponding values for the crop coefficient (Kc) are 0.4 (initial stage), 1.25 (peak season) and 0.75 (drying off phase). On an annual basis, the total water-use (ETc) is in the range 1100–1800 mm, with peak daily rates of 6–15 mm d−1. There is a linear relationship between cane/sucrose yields and actual evapotranspiration (ETc) over the season, with slopes of about 100 (cane) and 13 (sugar) kg (ha mm)−1 (but variable). Water stress during tillering need not result in a loss in yield because of compensatory growth on re-watering. Water can be withheld prior to harvest for periods of time up to the equivalent of twice the depth of available water in the root zone. As alternatives to traditional furrow irrigation, drag-line sprinklers and centre pivots have several advantages, such as allowing the application of small quantities of water at frequent intervals. Drip irrigation should only be contemplated when there are well-organized management systems in place. Methods for scheduling irrigation are summarized and the reasons for their limited uptake considered. In conclusion, the ‘drivers for change’, including the need for improved environmental protection, influencing technology choice if irrigated sugar cane production is to be sustainable are summarized.

Analysis of water application uniformity from a centre pivot irrigator and its effect on sugar beet ( Beta vulgaris L.) yield

The effect of water application uniformity (CU) on the uniformity of soil water content (CUs) and crop yield uniformity (CUyield) from a centre pivot irrigation system operating under field conditions was analysed. Rotating Spray Plate Sprinklers (RSPS) and Fixed Spray Plate Sprinklers (FSPS) were placed at 2.5 and 1 m above the ground. For individual irrigation events, RSPS had higher values of CU (90–95%) than the FSPS (80–85%). The value of CU corresponding to the series of accumulated irrigation depths (CUa) was more closely correlated with final crop yield than the values for individual irrigation events (CU). This was much more important with FSPS because of the method used to apply the water. In sprinkler irrigation, a CU value of around 80% for individual irrigation events can be sufficient to provide good crop yield uniformity since the corresponding CUs can easily exceed 90% since values of CU > 90% in individual irrigation events do not significantly increase water uniformity in the soil. The final sugar beet yield was affected more by the amount of water available in the soil than by the slight differences in soil water uniformity obtained with centre pivots. This behaviour is considered to be typical for this kind of sprinkler.

Characterisation of evaporation and drift losses with centre pivots

The objective of this paper is to study evaporation and drift losses (EDLs) with two types of sprinklers: rotating spray plate sprinklers (RSPS) and fixed spray plate sprinklers (FSPS), both installed at two different heights (1 and 2.5 m above the ground). A field test was carried out during three seasons at an irrigated plot with a centre pivot, in Albacete (Spain). The results show that EDLs were significantly higher with the FSPS placed 2.5 m above the ground (FSPS 2.5) than with the RSPS placed 1 m above the ground (RSPS 1). The EDLs obtained for the FSPS 2.5 combination were 8% for night irrigation events and 13.7% for daytime irrigation events. The lowest EDL values were registered with RSPS 1, ranging from 3.3 to 8.2% under night and day operation conditions, respectively. These results were obtained for an average wind speed of 1.3 m/s at night and 3.5 m/s during the day, and were normally below 5 m/s.

Assessment of the Impact of Irrigation with Low-quality Mine Water on Virgin and Rehabilitated Soils in the Upper Olifants Basin

Low-quality mine water from collieries may be used in large quantities to irrigate agricultural crops on virgin (unmined) and rehabilitated soils in South Africa. Such a use could enhance crop production and allow environmentally sustainable mine water disposal. In this study, the volume and qualities of the runoff from two centre pivots irrigated with moderately saline mine water, as well as their soil water salinities, were monitored and used to determine water and salt balances, using the modified ACRU agrohydrological model, ACRU2000, and its salinity module, ACRUSalinity. At both sites, much of the water evaporated, while a significant part of the salt input either precipitated or remained with the water in the soil horizons. A higher percentage of drainage water (and salinity) were retained as ground water storage and a lower percentage of runoff occurred in the rehabilitated sandy loam soil, while a higher percentage of salts accompanied runoff in the virgin clayey soils. Simulated salt saturation values indicate that many crops could be successfully irrigated at 100% yield potential at either site. Electrical resistivity surveys were carried out at both sites. A general decrease in resistivities with depth in both the virgin and rehabilitated soils reflected the decreasing influence of the mine water used for irrigation with depth and the precipitation of salts in the soils close to the ground surface. The occurrence of a thicker, low-resistivity, near-surface layer near the exit of each pivot area indicates that the water and salt content of the subsurface increased in the direction that the surface and near-surface irrigation water flowed.

Agricultural intensification and loss of matrix habitat over 23 years in the West Wimmera, south-eastern Australia

The global trend toward more intensive forms of agriculture is changing the nature of matrix habitat in agricultural areas. Removal of components of matrix habitat can affect native biota at the paddock and the landscape scale, particularly where intensification occurs over large areas. We identify the loss of paddock trees due to the proliferation of centre pivot irrigation in dryland farming areas as a potentially serious threat to the remnant biota of these areas. We used a region of south-eastern Australia as a case study to quantify land use change from grazing and dryland cropping to centre pivot irrigation over a 23-year period. We also estimated rates of paddock tree loss in 5 representative landscapes within the region over the same period. The total area affected by centre pivots increased from 0 ha in 1980 to nearly 9000 ha by 2005. Pivots were more likely to be established in areas which had originally been plains savannah and woodlands containing buloke ( Allocasuarina luehmannii), a food source for an endangered bird. On average, 42% of paddock buloke trees present in 1982 were lost by 2005. In the two landscapes containing several centre pivots, the loss was 54% and 70%. This accelerated loss of important components of matrix habitat is likely to result in species declines and local extinctions. We recommend that measures to alleviate the likely negative impacts of matrix habitat loss on native biota be considered as part of regional planning strategies.

Commercial production of crops irrigated with gypsiferous mine water

The use of gypsiferous mine water for irrigation of agricultural crops is a promising technology that could add value through agricultural production and utilise mine effluent. Crop response to irrigation with gypsiferous mine water, as well as the impact on soil and groundwater resources were investigated in a three-year field trial set up at Kleinkopje Colliery (Witbank, Mpumalanga Province, South Africa). Sugar-beans, maize and wheat were irrigated with four centre pivots on virgin and rehabilitated land, under three irrigation management regimes using two qualities of mine water. Good crop yields were obtained compared to dry-land cropping. Waterlogging in certain areas of the fields indicated that especially rehabilitated land should be properly prepared and, where necessary, waterways built to prevent yield reduction. Soil salinity increased over the duration of the trial due to high concentrations of Ca2+, SO42- and Mg2+ in the irrigation water, but this never reached levels critical to yields of most crops. Exchangeable Ca2+ and Mg2+ in the soil increased with time, whilst K+ decreased. Plant analyses indicated possible nutrient deficiencies, which should be easily managed through corrective fertilisation. The groundwater impact was limited based on borehole measurements, indicating the presence of a buffer zone between the cropped soil profile and groundwater, but this should be monitored over a longer period. Commercial production of crops under irrigation with gypsiferous mine water is feasible and the resulting environmental impact is limited, but further research is required to confirm these findings over a longer period. WaterSA Vol.28(4) 2002: 413-422