Irrigation sustainability – Saskatchewan activity

By L.C. Tollefson and T.J. Hogg

Abstract

Irrigation is essential for world food production. In Western Canada, it has historically been viewed as a mechanism for stabilizing agricultural production by overcoming problems associated with drought and allowing for the diversification of crop production. It is critical that the long term environmental effects of irrigation be understood if the negative impacts on soil and water are to be avoided and irrigation is to continue its contribution to the diversification of agriculture. The Canada-Saskatchewan Irrigation Diversification Centre (CSIDC), located at Outlook, Saskatchewan, has developed an applied research and demonstration program designed to evaluate irrigation sustainability. Four project areas were identified: (1) pesticide and nutrient losses and groundwater contamination under irrigated conditions; (2) evaluation of the effects of irrigation on soil quality; (3) water conservation and water use efficiency; and (4) effluent irrigation management. These programs were delivered by the CSIDC and funded through the Canada-Saskatchewan Agriculture Green Plan Agreement (CSAGPA).

Introduction

Throughout history, water resources and irrigation development have played a major role in human development. Most of the growth in food production needed to meet population increases over the past four decades has resulted from an expansion of the irrigated area. The world's 260 million irrigated hectares of land (which is one sixth of the world's cropped land) now produces greater than one third of the world's food supply (Wolter & Kandiah, 1997).

Irrigation development, however, also introduces major changes in the environmental and socio-economic conditions of these areas. In the process, existing equilibria are disturbed and over time, new ones established with the underlying premise that the new conditions established satisfy human kinds' objectives better than those practiced before (Pereira et al., 1996). Irrigation development, while contributing to the economic well being of many countries, has potential negative effects. Questions have arisen whether irrigation is capable of continuing the high level of agricultural production in the longer term without damaging the environment (Pereira et al., 1996).

In Western Canada, irrigation has historically been viewed as a mechanism for stabilizing agricultural productivity by overcoming problems associated with drought and allowing for crop diversification to occur. It has been estimated in Alberta, for example, that 20% of the province's agricultural production comes from 4% of the arable land which is irrigated.

Despite the increased production, diversification and associated economic benefits, the sustainability of irrigation is questioned. This is largely due to its sometimes detrimental effect on the environment (waterlogging, soil salinity and groundwater contamination). It is important that the long term environmental effects of irrigation be understood if the negative impacts on soil and water are to be avoided.

The Canada-Saskatchewan Irrigation Diversification Centre (CSIDC), located at Outlook, Saskatchewan, has played an important role in advancing irrigation technology. The Centre has conducted, funded and facilitated many irrigated research and demonstration projects in Saskatchewan. Although the initial emphasis at CSIDC was crop diversification through varietal and agronomic evaluation, more recently emphasis has been placed on resource care issues.

The Canada-Saskatchewan Agriculture Green Plan Agreement (CSAGPA) was a federal/provincial agreement signed in 1991. Its objective was to improve resource management by promoting environmentally sound production practices in the primary production and processing sectors. Irrigation sustainability was identified as a key component area and CSIDC was requested to be the delivery agent. The following paper outlines the process involved and highlights the resulting program.

Irrigation Sustainability Technical Committee

An irrigation sustainability technical committee was established to identify, review and prioritize research and demonstration activity in support of the irrigation sustainability component of CSAGPA.

This committee served as an advisory committee to the Implementation Committee for matters of policy and procedure. The chairperson was appointed by Agriculture and Agri-Food Canada, PFRA, and the membership included up to eight technical experts from Agriculture and Agri-Food Canada (PFRA and Research Branch), National Hydrology Research Institute, Saskatchewan Water Corporation and the University of Saskatchewan.

This committee identified four priority areas of study related to irrigation sustainability: 1) pesticide and nutrient losses and groundwater contamination under irrigated conditions; 2) evaluation of the effect of irrigation on soil properties; 3) water conservation and water use efficiency; and (4) effluent irrigation management.

Near the end of the program, three additional smaller studies were initiated:
i) production of a trickle irrigation manual; ii) literature review of emerging centre pivot application technology; and iii) data synthesis of a hog effluent irrigation project.

Projects

I. Managing Herbicides, Pesticides and Water for Sustainable Irrigated Agriculture

(A. Cessna, Agriculture & Agri-Food Research Branch; W. Nicholaichuk and J. Elliott, National Hydrology Research Institute; L. Tollefson, Saskatchewan Irrigation Development Centre).

Contamination of surface and groundwater sources by N fertilizer and pesticides has been well documented in the USA (Fairchild, 1987; Johnson & Cross, 1990). Pesticides were first found in the groundwater in 1979. Prior to that, it was generally believed they did not leach into the groundwater. The detection of N and pesticides have also been reported in Western Canada (Miller et al., 1992; Nicholaichuk et al., 1992).

Irrigation water provides a driving force for the downward leaching of chemicals, hence the amount of water applied will potentially affect the movement of chemicals to groundwater (Bouwer, 1987).

This project had the objective of quantifying the movement of nutrients and commonly used pesticides under irrigated conditions in Saskatchewan. Work conducted under an irrigated scenario provides the worst case scenario for a dryland production. The long term intent was to develop best management practices. The issues addressed are as follows:

a) Establishment of a tile drained field laboratory for evaluating leaching and preferential flow of pesticides and nutrients through the vadose zone. A replicated tile drained site (10 ha) was established at SIDC in the spring of 1994. Physical characteristics of the site were determined by measuring bulk density, infiltration rates, hydraulic conductivity and ground probing radar. A network of suction lysimeters were also installed for collecting soil water samples.

Equilibration of the site was initiated in the fall of 1994 and continued in 1995 and 1996 by applying leaching water to flush excess soluble salts from the soil above the drains. During the leaching period, tile drain effluent was collected using automatic water samplers equipped with integrated flow meters while soil water extract was collected from the suction lysimeters. The water samples are being analyzed for salts, nutrients and herbicides. Changes in the soil salinity were monitored before and after leaching using a non-contacting electromagnetic terrain conductivity meter (EM 38).

After equilibration, the tile drained site will be utilized by the Water Quality Technical Group of CSAGPA to study various management options under irrigated conditions. This will include the timing of irrigation in relation to pesticide and fertilizer application, fertigation compared to other means of fertilizer application, etc. These options will be evaluated by monitoring tile effluent quality and quantity along with analysis of the soil water extract.

b) Pesticide and nutrient loadings to the South Saskatchewan River in irrigation return flow water. Monitoring of irrigation water return flow to the South Saskatchewan River Irrigation District No. 1 (SSRID No. 1) was conducted during the 1994, 1995 and 1996 growing seasons. Two drainage ditches (1C and 9A), which drain a major portion (70%) of the surface irrigated area in SSRID No. 1 were monitored for flow rate, major nutrients (nitrate, total P and ortho P) and several herbicides (2,4-D, dicamba, MCPA, trifluralin, triallate, bromoxynil, diclofop, mecoprop and clopyralid). One drainage ditch exits directly into the South Saskatchewan River and was monitored at that point. The second ditch passes through a natural wetland before exiting to the river. This ditch was monitored at two locations: one location was upstream from the wetland and the other downstream from the wetland at the point where the return flow enters the river. Automated samplers were used at all locations, composite water samples (subsample collected every hour) were collected daily from May 1 to September 30. Daily integrated outflow was determined. Information regarding fertilizer and pesticide use patterns on surface-irrigated fields drained by the respective ditches was obtained to aid in interpreting the residue data.

Preliminary results, from 1994 and 1995, indicate low nitrate levels (<1 mg L^-1). Phosphorus levels in approximately 25% of the samples exceeded the water quality guideline for phosphorus in flowing water at 0.1 mg L^-1. In 1994, MCPA, 2,4-D dicamba and bromoxynil were the only herbicides detected in the 1C drainage ditch. Peak concentrations of MCPA, dicamba and bromoxynil were detected at progressively later dates as the water moved downstream. In general, maximum herbicide concentrations tended to decrease as the drainage water moved more progressively downstream. 2,4-D was the only herbicide which was detected in all water samples from all sampling stations and, in contrast to MCPA, dicamba and bromoxynil, showed two concentration maxima. One concentration maxima occurred during the June/July spraying season and the other during mid-September to early October. Only 2,4-D, MCPA and dicamba were detected in the drainage water from the 9A drainage ditch. In the drainage water from both ditches, maximum concentrations of dicamba and bromoxynil were less than 0.1 mg/L whereas that of the MCPA was ~ 0.3 mg/L. The spring maximum concentration for 2,4-D was ~ 0.6 mg/L whereas that for the fall was ~ 5 mg/L. Only the fall maximum concentration of 2,4-D exceeded the Canadian Water Quality Guidelines for irrigation.

II. Evaluation of the Effects of Irrigation on Soil Chemical and Physical Properties (Prof. J.L. Henry, University of Saskatchewan, Soil Science, and T.J. Hogg, SIDC)

The long term effect of irrigation on soil chemical and physical properties as they relate to soil productivity require quantification. Irrigation encourages continuous cropping of land. Continuous cropping can have beneficial effects on soil properties (Campbell et al., 1990). Improved yield and increased organic matter levels have been observed under long term irrigated rotations (Dubetz, 1983). Irrigated production has also been shown to increase the total nitrogen and carbon in cases where these values were low in the native condition (Lueking and Schepers, 1985). Further work is required to document the long term changes in soil properties as affected by irrigation.

The objective of this project was to document the effect of irrigated agriculture on the chemical, physical and microbiological properties of soils and on the subsoil accumulation of nutrients.

A major soil sampling and analytical program was initiated. Twelve paired irrigation and dryland sites within the SSRID No. 1 were sampled. Non-saline soils were specifically chosen to assess the effects of irrigation on soil properties excluding salinization.

The results suggest no significant difference in bulk density or pH between irrigated and dryland treatments. Annual application of ammonia-based fertilizers, such as urea and anhydrous ammonia, did not reduce soil pH. The dryland treatment maintained significantly higher water aggregate stability (WAS) than the irrigated treatment. Irrigation results in aggregate destabilization either through rapid organic matter (OM) breakdown and mineralization, or continuous years of waterdrop impact. When divided into three textural classes involved (LS, SL and L), the reduction in WAS of the irrigated treatment was only significant in the loam soil. When divided into replicates managed by the same producer, it was evident individual agronomic management influenced aggregate stability. Practices which did not return crop residue or encouraged tillage resulted in a decrease of stable aggregates.

The results also indicated that irrigated management altered nutrient availability. The irrigated treatment contained significantly higher NO₃-N than the dryland soil (23 ug g^-1 versus 9 ug g^-1 respectively). The significant difference in NO₃-N levels may be attributed to: (1) greater amounts of ammonia-based fertilizer application on irrigated land, (2) annual fertilizer application on irrigated land and (3) greater mineralization of N in irrigated land than dryland.

Nitrogen mineralization in the irrigated treatment was greater than in the dryland treatment. Subsequent plant uptake of the available N was greater in the irrigated than the dryland treatment. Greater plant uptake in the irrigated treatment was attributed to a greater initial NO₃-N content. Influence of management was evident for mineralization when the replicates were segregated into those farmed by the same producer. Management practices of irrigated land, including yearly fertilizer application, results in the addition of young, labile OM to irrigated soil which contributes to the mineralization of organic N. The labile OM acts as a substrate for microorganisms and is readily decomposed, turning over large amounts of N.

The total OM content, however, of the irrigated treatment did not increase. Static OM levels, increased mineralization, relatively high NO₃-N levels and increased uptake of available N within the irrigated treatment stress the importance of OM quality. The rapid cycling of OM in irrigated soils results in increased plant uptake of readily available nutrients and greater soil fertility.

The N supply experiment assisted in verifying a number of conclusions:

1. Irrigated soils could supply significantly greater amounts of NO₃-N than dryland soils;
2. Irrigated soils contain greater amounts of NO₃-N and mineralized more N than dryland soils. This suggests the ability of irrigated soils to convert organic N to inorganic plant available N and improve the fertility of irrigated soils above that of dryland soils.

The N supply experiment also suggested initial NO₃-N is strongly correlated with N uptake and yield. The mineralized N, determined by a two week incubation method, however, was not highly correlated with N uptake and yield. The N supply rate, which considers the level of initial NO₃-N and the mineralized N, is almost equal to the initial NO₃-N when reflecting N uptake or yield.

Irrigated treatments maintained higher P levels than dryland treatments. The increase in P can be attributed to greater P fertilization of irrigated soil than of dryland soil. From 1992 to 1995, the average P₂O₅ application rate for irrigated land was 39 kg ha^-1, while the average for dryland was 5 kg ha^-1.

Although not significant, trends of greater SO₄-S and less K in the irrigated treatment were evident. The SO₄-S levels in the irrigated treatment were tending towards the equilibrium with the SO₄-S in the irrigation water. A decreasing trend of K within irrigated land may be occurring because yearly harvests of high yielding crops are removing K from the field and K fertilizer is not used to maintain the K reserve.

No detectable differences in soil algal biomass were measured.

The differences in soil parameters of the irrigated and dryland treatments were mainly attributed to management differences. Before irrigation began in the 1960s, the soils of the irrigated and dryland treatments were pedologically similar. The observed differences, therefore, are a result of management at two levels: (1) long-term irrigation management and (2) specific producer management practices. Management of the irrigated land includes continuous cropping, yearly application of irrigation water and fertilizer. By comparison, the dryland soils within this study received less fertilizer and were sometimes fallowed. It was apparent that irrigated soils have a greater ability to mineralize and supply N. Fertility of irrigated soils improved with long-term irrigation management.

Another aspect of this project looked at the movement of nutrients through the soil profile to surface aquifers. Deep soil cores were collected at three landscape positions in each of two irrigated and two dryland fields to determine the effect of irrigation on the subsoil accumulation of nutrients. Analysis of the samples collected indicated a slight increase in NO₃-N content in the knoll landscape position. The general conclusion to be drawn from this work is that contamination of the vulnerable surface aquifer with nitrate is not likely under the present management system.

III. Water Conservation and Water Use Efficiency (J. Gillies, U of S, Ag & Bioresource Engineering; L. Tollefson, SIDC).

Water conservation and water use efficiency are critical issues. Like other uses, irrigation is coming under increasing pressure to use water efficiently. Many irrigators in Canada have traditionally had an ample water supply, hence water conservation methodology has not been practiced. Excess irrigation can have a detrimental effect on the environment through water logging and increased soil salinity. Under irrigation can lead to reduced crop yield. Water management and water conserving technology play an important role in reducing both energy costs and water use (Negi and Hanchar, 1989; New and Fipps, 1990). Developments in lower pressure water application technology for irrigation systems have demonstrated opportunities for both water conservation and cost reduction from decreased energy consumption. Research is required in improved application technologies and water management practices for the prairie region.

The following were studied in this project:

a) Nozzle studies. A nozzle/system study was conducted to determine the following parameters for centre pivot and linear systems that are commonly operated in Saskatchewan: water distribution efficiency, application uniformity and application efficiency; energy used when operating at high and low pressures and at various drop tube heights; and the effect of wind speed on application uniformity.

The field component of this study was conducted at SIDC using field scale centre pivot and linear move irrigation systems. The laboratory component was conducted in the Hardy Laboratory of the Department of Agricultural and Bioresource Engineering, University of Saskatchewan (Opoku, 1995).

The data collected was used to determine the relationships that exist between energy utilized, application efficiency, nozzle and system type, operating pressure and climatic conditions.

b) System studies. Included in this study is an evaluation of the potential for implementation of Lower Elevation Spray Application in Saskatchewan. Modification of a high pressure centre pivot irrigation system at SIDC was conducted in 1994 to compare low energy, low elevation sprinkler application (LESA) with conventional high pressure impact sprinkler application. Soil moisture, plant water use, system flow rates, pressure (energy) inputs and crop yield were monitored.

While comparing the coefficients of uniformity for the high and low pressure sides of the modified centre pivot system, it was found that the high pressure side maintained uniformity of application throughout varying wind conditions. The low pressure side indicated an increase in the coefficient of uniformity as wind speed increased. It was not practical to measure the coefficient of uniformity of the LESA technology since the nozzles were below the crop canopy. Thus, the result of increasing uniformity with the LESA technology suggests that the coefficient of uniformity can be expected to exceed that of the standard impact technology under low or "no" crop conditions.

The application efficiency of the high and low pressure components indicated that the low pressure component had a better efficiency at all wind speeds. The high pressure side ranged from 86% at a wind speed of 3 km/h^-1 to 69% at a wind speed of 32 km/h^-1 while the low pressure component ranged from 98% at 5 km/h^-1 wind speed to 74% at 37 km/h wind speed. Both the high and low pressure components displayed increased energy consumption as wind speed increased. Average energy consumption indicated that the energy cost of operating a LESA centre pivot was approximately one half that of operating a standard impact nozzle centre pivot.

Monitoring both low and high pressure farm scale irrigation systems is currently being conducted in conjunction with a PAWBED funded project.

IV. Effluent Irrigation Guidelines and Management Practices

Effluent irrigation has been practiced for centuries (Shuval et al., 1986). It provides farmers with a nutrient enriched supply of water and society a reliable inexpensive system for tertiary treatment and disposal of wastewater (Feigin et al., 1991). Effluent use has primarily been limited to forage production in Western Canada to avoid direct human consumption of contaminated plant products (Biederbeck, 1982). However, as the number of projects increase, there is a growing demand for effluent use on non-forage crops (Davies et al., 1988; Kirkham, 1986).

In Saskatchewan, there are three major centres, Swift Current, Moose Jaw and Lloydminster, and 28 smaller communities which conduct effluent irrigation. Some communities view effluent irrigation as a means of municipal effluent disposal while others view municipal effluent as a resource for economic development through either cash crop production or golf course irrigation. An understanding of the sustainability of such projects is of interest not only to those involved but to society in general.

The objective of this project was to establish site selection guidelines and management practices for sustainable municipal effluent irrigation projects.

The project was conducted for SIDC by Normac A.E.S. Ltd. It was done in the following phases:

Phase I: Review international literature and other information sources to determine effluent irrigation standards used in other jurisdictions.

Phase II: Analyze existing monitoring data from selected effluent irrigation sites in Saskatchewan.

Phase I - International literature review. A comprehensive international literature review was conducted. Topics included a description of the alternative uses of wastewater including agricultural irrigation; a review of the history of effluent irrigation with emphasis on health risks; overcoming the health risks of wastewater use; types of sewage treatment; a review of wastewater reuse and standards used in other countries; general standards adopted by various jurisdictions in the United States and Western Canada; and general site selection and monitoring guidelines used with effluent irrigation.

Health guidelines for irrigation with treated wastewater developed in California, for example, indicate that for agriculture reuse of effluent waters on food crops, the wastewater must be disinfected, oxidized, coagulated, clarified and filtered. Total coliform counts cannot exceed a median value of 2.2/100 ml or a single sample value of 25/100 ml. Total coliforms must be monitored daily. Turbidity cannot exceed 2 NTU and must be monitored continuously. Less restrictive guidelines developed by Dr. Shuval from Israel, and adopted by most of the international agencies, indicate that effluent water reuse was relatively safe to use if it contained less than 1 helminth egg/litre and less than 1000 fecal coliforms/100 ml.

Guidelines for acceptable salinity and minor element levels in effluent waters for irrigation follow those set for normal irrigation waters. Soluble salt levels are limited to less than 2000 mg L^-1. Most of the soluble salts added to the soil during irrigation will reach the shallow groundwater and increase the salt concentration in domestic wells and springs. They become part of the return flow of groundwater to local rivers and streams.

Phase II - Analysis of monitoring data. Analysis of monitoring data from the Moose Jaw and Swift Current municipal effluent irrigation projects was conducted to determine or help predict the sustainability of these projects and to assist in setting guidelines for future projects. Data collected from the Moose Jaw rapid infiltration basin displayed a phosphorus removal efficiency of 80% over five years. Although organic and ammonium nitrogen removal efficiency exceeded 90%, the N removal efficiency was 60% because of the conversion of the nitrogen to the more mobile nitrate form. Under field conditions, efficiencies are much higher due to slower application rates (1 m/year) and higher plant use. At Swift Current chloride levels have increased from 10 to over 300 mg L^-1 in some of the shallow monitoring wells and domestic wells in the effluent irrigation project.

Other Projects

Three additional smaller projects were initiated and completed near the end of the CSAGPA Program. These included:

a) Trickle Irrigation (W. King)

A basic trickle irrigation manual was developed which outlined the principals, components, operation and system design.

b) Emerging Centre Pivot Water Application Technology (G. Snaith)

A literature review was conducted on lower pressure water application technology for centre pivots. The potential for energy and water saving using this new technology was reviewed with particular emphasis on Western Canada.

c) Elite Stock Farm Hog Effluent Project (J.L. Henry)

Funding was provided to summarize and analyze data from the Elite Stock Farm Effluent Irrigation Project.

Conclusion

The effects of irrigation on the environment are critical to the long term sustainability of irrigation. Funding from the CSAGPA provided SIDC the resources to formulate a team and initiate work in this area. Final reports are available for the work now completed. Continued study will be critical to the viability of the irrigation industry in the future.

References

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