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Published in J. Environ. Qual. 33:2290-2295 (2004).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORTS

Waste Management

Pig Slurry Application and Irrigation Effects on Nitrate Leaching in Mediterranean Soil Lysimeters

A. Daudén, D. Quílez* and M. V. Vera

Unidad de Suelos y Riegos, Centro de Investigación y Tecnología Agroalimentaria de Aragón Apdo. 727, 50080-Zaragoza, Spain

* Corresponding author (dquilez{at}aragon.es)

Received for publication July 10, 2003.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Land application of animal manures, such as pig slurry (PS), is a common practice in intensive-farming agriculture. However, this practice has a pitfall consisting of the loss of nutrients, in particular nitrate, toward water courses. The objective of this study was to evaluate nitrate leaching for three application rates of pig slurry (50, 100, and 200 Mg ha–1) and a control treatment of mineral fertilizer (275 kg N ha–1) applied to corn grown in 10 drainage lysimeters. The effects of two irrigation regimes (low vs. high irrigation efficiency) were also analyzed. In the first two irrigation events, drainage NO3–N concentrations as high as 145 and 69 mg L–1 were measured in the high and moderate PS rate treatments, respectively, in the low irrigation efficiency treatments. This indicates the fast transformation of the PS ammonium into nitrate and the subsequent leaching of the transformed nitrate. Drainage NO3–N concentration and load increased linearly by 0.69 mg NO3–N L–1 and 4.6 kg NO3–N ha–1, respectively, for each 10 kg N ha–1 applied over the minimum of 275 kg N ha–1. An increase in irrigation efficiency did not induce a significant increase of leachate concentration and the amount of nitrate leached decreased about 65%. Application of low PS doses before sowing complemented with sidedressing N application and a good irrigation management are the key factors to reduce nitrate contamination of water courses.

Abbreviations: LF, leaching fraction, PS, pig slurry


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
SPAIN IS THE second leading European country in swine population (22.4 million head in 2000), representing 18% of total production within the European Union, with a substantial increase over the last ten years (38% from 1990 to 2000). The application of PS to soils, in many cases for waste-disposal purposes, is a common practice in agricultural areas. However, PS should be managed on the basis of its nutrient value to maximize its fertilizer value and avoid negative environmental pitfalls. Adequate PS applications can be sufficient to achieve satisfactory yields and can substitute for mineral fertilizers in many crops (Daudén and Quílez, 2004). However, as with mineral fertilizers, N in PS can leach out of the crop root zone and reach surface or ground water. Excessive applications of liquid pig manure could result in nutrient accumulation in the soil, thereby increasing the potential for plant nutrient loss through movement into ground water (Hountin et al., 1997). Although there is an increased risk of nitrate leaching from soils receiving high levels of liquid manure (Nielsen and Jensen, 1990; Beckwith et al., 1998; Jensen et al., 2000), it has been observed that, when applied at adequate rates, lower or similar amounts of nitrate are leached compared with systems using mineral fertilizers (Beauchamp, 1986; Zebarth et al., 1996; Randall et al., 2000; Díez et al., 2001; Daudén and Quílez, 2004).

Most studies dealing with the use of PS as fertilizer have been performed in northern Europe, where soils and climatic conditions differ from those found in Mediterranean soils. However, the processes involved in the N cycle are sensitive to soil properties, climatic characteristics, and management practices (Zebarth et al., 1996). In particular, the management of irrigation, a prerequisite for profitable crop production in Mediterranean semiarid areas (Fereres and Ceña, 1997), plays an essential role in nitrate movement in soils (Díez et al., 2000; Sexton et al., 1996; Spalding et al., 2001; Cavero et al., 2003). Surface irrigation is the main irrigation system in Spain (60% of the total irrigated land). Water and nitrate losses below the crop's root zone are almost unavoidable in the conventional management of surface irrigation due to its typical low efficiency and uniformity (Isidoro et al., 2003). Typical problems include (Faci et al., 2000) distribution systems with capacity below the peak demand; inflexible delivery rates, usually in 24-h shifts; poor on-farm land leveling; high ramification of the distribution systems; and small plots. On the other hand, properly designed and managed irrigation systems allow more uniform and efficient application of irrigation water that should minimize water and nitrate losses through deep percolation (Cavero et al., 2003).

Our objective was to evaluate the effects of three PS application rates and two irrigation efficiencies (traditional and high efficiency) on corn yield and on concentration and amount of nitrate leached, under a semiarid irrigated Mediterranean environment.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Experimental Design
The experiment was conducted in 1997 at the experimental farm of the Agronomic Research Service (Gobierno de Aragón, Zaragoza) using 10 drainage lysimeters of 1.5 m2 and 0.75 m deep with an exit at the bottom that permitted drainage collection at atmospheric pressure. Each lysimeter's drainage was collected when the soil at the bottom of the lysimeter was at saturation. In field conditions drainage occurs also under unsaturated conditions. The difference in the boundary conditions at the bottom of the lysimeters could slightly affect the drainage volume and nitrate concentration for a particular irrigation event but errors should be small when values are averaged over the season, considering that most of the drainage in surface-irrigated plots occurs under saturated conditions. Lysimeters were filled with a clay loam soil (303 g kg–1 sand, 411 g kg–1 silt, and 286 g kg–1 clay) with an organic matter content of 18 g kg–1. Soil bulk density ranged from 1.24 to 1.41 g cm–3 in the 0- to 0.3-m depth layer and from 1.34 to 1.56 g cm–3 in the 0.3- to 0.7-m depth layer. The average water content at field capacity was 25.6 g g–1 and at wilting point, 15.4 g g–1. Saturated hydraulic conductivity was estimated to be 5.41 mm h–1 using the Rosetta software (Schaap et al., 2001) for the above-given soil characteristics. Lysimeters were successively cropped with corn for the six years before the beginning of this experiment. Five treatments were designated in a randomized block design with two replicates. The amount of PS applied was 50 Mg ha–1 for treatments PS1 and PS1HE, 100 Mg ha–1 for treatment PS2, and 200 Mg ha–1 for treatment PS3. Treatments PS1 and PS1HE were complemented with 125 kg N ha–1 (ammonium nitrate) at sidedress. In the control treatment (PS0) the amount of N applied was 275 kg N ha–1 (i.e., the amount recommended in the area for the expected 10 Mg ha–1 corn grain yield), 100 kg N ha–1 before plant seeding and 175 kg N ha–1 at sidedress. Treatments PS0, PS1, and PS1HE were supplied with the required amounts of P and K, so these nutrients would not be yield-limiting factors. In the PS2 and PS3 treatments PS covered the whole P and K crop's needs. The physicochemical characteristics of the PS and the amount of N applied in each treatment, considering the ammonium fraction as the available N in PS, are presented in Tables 1 and 2, respectively.


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  		Table 1. Physicochemical characteristic of the pig slurry.

 

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  		Table 2. Amount of available nitrogen applied, measured leaching fraction (LF), yield, and nitrogen in the aboveground biomass (AGB) in the different pig slurry (PS) treatments.

 
The PS2 rate of 462 kg N ha–1 was chosen to evaluate the effect of a single PS application that satisfied the nitrogen needs for corn. The amount of N is more than the recommended N fertilization rate, but it is the normal rate applied by farmers in the area. The PS1 rate of 231 kg N ha–1 was selected to evaluate the application of PS in spring, before sowing, complemented with mineral N at sidedress. The high PS3 rate of 924 kg N ha–1 was selected to evaluate the detrimental environmental effects when fields are used as waste disposal landfills for PS effluents in areas of high swine density.

Treatments PS0, PS1, PS2, and PS3 followed traditional irrigation practices in surface-irrigated areas of the Ebro River basin, where irrigation efficiencies are low and leaching fractions (LF), defined as the amount of percolating water to that of irrigation water, are high (Aragüés et al., 1985). Thus, a target LF of 0.4 was selected for these treatments. To observe the effect of a better irrigation management on drainage water quality, treatment PS1HE followed a high-efficiency irrigation practice with a target low LF of 0.1. This LF is sufficient to satisfy the leaching requirement of corn for the salinity of the applied irrigation water (electrical conductivity < 0.8 dS m–1) (Ayers and Westcot, 1994).

Liquid manure was applied on 30 Apr. 1997 and mixed thoroughly with the soil to minimize volatilization losses. On 9 May, corn (Zea mays L. cv. Juanita) was sowed in two rows at a distance of 0.75 m with a plant density of 80000 plants ha–1. Sidedress fertilization (ammonium nitrate) was applied on 20 June 1997 to treatments PS0, PS1, and PS1HE. Lysimeters were irrigated using a hose pipe and the amount of water applied was measured using a flow meter. Ten irrigations were conducted between 12 June and 3 September, with intervals ranging from 7 to 10 d depending on climatic conditions and crop development. The amount of irrigation water applied during the crop cycle was 1280 mm in the four treatments (PS0, PS1, PS2, and PS3) and 860 mm in Treatment PS1HE. Average nitrate concentration in irrigation water was 8 mg L–1 ranging between 6 and 11 mg L–1. Nitrogen applied with the irrigation water was 17.3 kg NO3–N ha–1 in treatments PS0, PS1, PS2, and PS3, and 11.6 kg NO3–N ha–1 in Treatment PS1HE. The total rainfall during the crop period was 186 mm. The leaching fraction, including precipitation, was 0.16 in treatment PS1HE (target LF = 0.1) and ranged between 0.37 and 0.47 in the other four treatments (target LF = 0.4) (Table 2).

Sampling and Analytical Procedures
The soil was sampled on 15 April (before PS application) and on 1 October (after harvesting). Two samples per lysimeter (with a 5-cm-diameter manual auger) were taken at 0- to 0.3-, 0.3- to 0.6-, and 0.6- to 0.75-m depth increments. The holes created were backfilled with original soil and compacted properly to avoid posterior preferential flows.

Soil water content was measured by drying a part of the samples at 105°C for 48 h. The rest of the samples were air-dried, ground, and sieved to 2-mm. Nitrate concentrations were determined in 1:3 soil to saturated calcium sulfate solution extracts (Sempere et al., 1993).

On 30 Sept. 1997 the plants were harvested and grain yield and aboveground dry biomass were measured. Moisture content and specific weight of grain were measured using an Aquasearch 600 grain moisture meter (Kett Electric Laboratory, Tokyo, Japan). A sample of three whole plants was taken from each lysimeter for the analysis of total N by a Kjeldahl method (Ministerio de Agricultura, Pesca y Alimentación, 1992).

Drainage was collected in graduated 50-L plastic containers connected with a tube to the bottom exit of each lysimeter. The volume of drainage was measured after each irrigation and precipitation event, and drainage water samples were taken for analysis of nitrate concentration. Data for some other forms of nitrogen in the drainage water were not reported because they are generally negligible or undetectable compared with nitrate. Prunty and Montgomery (1991), in an experiment in corn fertilized with urea in 2.3-m-deep lysimeters, found ammonium concentrations in leachate below 0.1 mg NH4–N L–1, which was negligible compared with NO3–N concentrations. Martínez (1997) used a 0.8-m-deep soil as a treatment process for PS. During the five years of his experiment, with a mean annual application rate of 3246 kg NH4–N ha–1, annual average nitrate concentrations in the leachate were between 290 and 940 mg NO3– L–1 and ammonium concentrations in the range 0.12 to 1.2 mg NH4+ L–1. In addition, Kengni et al. (1994) found that NH4+ was generally not present in the soil solution of soil samples tested under laboratory conditions to quantify the process of mineralization.

Nitrate concentrations in drainage waters and soil extracts were determined by ion chromatography (Model 2001 SP; Dionex, Sunnyvale, CA).

Data Analysis
Evapotranspiration in each lysimeter was estimated by the water-balance method for the period 15 Apr.–1 Oct. 1997 using the initial and final soil water contents and the volume of irrigation, precipitation, and drainage. Nitrate loads in drainage waters were calculated for each drainage event as the product of drainage volume and nitrate concentration. The flow-weighted average nitrate concentration for the study period was obtained by dividing the total nitrate load by the total drainage volume.

The SAS MIXED model (SAS Institute, 1991) with the REPEATED statement for sampling time was used to analyze concentration and mass of nitrate in drainage (Littell et al., 1998). Both variables were normalized using a log transformation before the analysis. PROC MIXED in the SAS system permits modeling the covariance structure of the data. The autoregressive structure of order 1 within treatments and a random effect between treatments was indicated as best among the three covariance structures tested (compound symmetric, unstructured, and autoregressive of order 1 + random effect) on the basis of the Schwarz Bayesian criterion. There was not a significant interaction between treatments and sampling times. Differences between treatment means (N rates for target LF = 0.4, and LF for the 50 Mg ha–1 PS rate) averaged over sampling times were obtained using orthogonal contrasts at the 95% confidence level (p = 0.05).

A nitrogen budget was calculated for each lysimeter including as inputs the initial nitrate content in the soil, the nitrate in irrigation and rainwater, and the N inputs from slurry and mineral N fertilizers. For the PS treatments, only the amount of inorganic N (NH4–N) applied with the PS was considered. The outputs included the final nitrate content of the soil, the N extracted by the crop including roots, and the nitrate leached. Nitrogen in the roots was estimated by assuming that the dry roots amount to 15% of aerial plant mass and also estimating the root N concentration to be half of that of the aerial biomass (Mitchell and Teel, 1977). Unaccounted N was obtained as the difference between outputs and inputs and included the net mineralization of organic matter, gaseous losses by volatilization and denitrification, immobilization or fixation of the applied N, and inorganic N forms different than nitrate in the soil and in the irrigation and drainage water.

Regression analysis (p = 0.05) was used to evaluate the effect of available N rates on the analyzed variables for the target LF = 0.4 treatments while analysis of variance (p = 0.05) was used to evaluate the effect of improved irrigation efficiency (PS1 vs. PS1HE). Statistical analysis was obtained with the statistical package SAS (SAS Institute, 1991).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
The average nitrate content of the soil across all treatments for the 0- to 0.75-m depth was 128 kg NO3–N ha–1 (standard deviation = 32 kg NO3–N ha–1) at the beginning of the experiment, and then decreased to 11 kg NO3–N ha–1 (standard deviation = 1.6 kg NO3–N ha–1) at the end of the cropping period due to crop N extraction and nitrate leaching. No significant differences were detected between treatments at both dates. The high rates of nitrogen applied in the PS3 treatment did not produce higher values of nitrate concentration in the soil at the end of the crop cycle.

The estimated average corn evapotranspiration (ET) ranged between 827 and 964 mm with an average value of 903 mm, which is 50% higher than the normal corn ET of 600 mm for the area (Farré, 1998). The lysimeters were aboveground and without border plants, resulting in greater plant light exposure and, consequently, in higher ET, yield, and biomass production (Monteith, 1969).

Crop Yield and Nitrogen Uptake
The high PS dose given before sowing in treatment PS3 produced emergence problems, probably due to ammonium toxicity (Pratt, 1979). Grain yield ranged between 16.7 (PS0) and 22.0 Mg ha–1 (PS2 and PS1HE) and aboveground dry matter (AGDM) between 33.2 (PS0) and 40.6 (PS2 and PS1HE) Mg ha–1 (Table 2). The water use efficiency estimates (ranging between 1.79 and 2.40 g grain L–1 and 3.88 to 4.44 g AGDM L–1) were typical for well-irrigated corn in the area (Farré, 1998). Total N in aboveground biomass (Table 2) ranged between 194 kg N ha–1 (PS0) and 305 kg N ha–1 (PS2).

Optimum rate of N fertilization for the target LF = 0.4 estimated by the linear-response plateau model using yield data was 366 kg N ha–1 (asymptotic 95% confidence interval = 248–483 kg N ha–1). The estimated technical optimum rate would indicate that treatment PS0 was under-fertilized and PS3 over-fertilized, and PS1 and PS2 can be included in the well-fertilized range.

Nitrate in Drainage
Drainage nitrate concentrations tended to decrease with time (Fig. 1) . After the first irrigation (12 June), the average drainage NO3–N concentration for all treatments was 63 mg L–1, which decreased to 13 mg L–1 after the fourth irrigation (16 July) as a consequence of plant N uptake and the subsequent N decrease in the soil (Kengni et al., 1994), and was lower than 6.5 mg L–1 afterward. Drainage NO3–N concentrations as high as 145 and 69 mg L–1 were measured in PS3 and PS2 (where only PS was applied) in the first two irrigations, indicating the fast transformation of the PS ammonium into nitrate and the subsequent leaching of the transformed nitrate (Jensen et al., 2000; Martínez and Peu, 2000). After the first three irrigations (10 July), more than 82% of the total mass of nitrate in drainage was leached in all treatments (Fig. 2) , indicating that the susceptibility to nitrate leaching was higher in the earlier phases of crop development.



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  		Fig. 1. Average NO3–N concentration (mg L–1) in drainage during the period 1 May–1 Oct. 1997 for the different treatments. Irrigation started on 12 June 1997 (first arrow) and sidedress nitrogen was applied on 20 June 1997 (second arrow). Vertical lines indicate one standard deviation. See Table 2 for treatment descriptions.

 


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  		Fig. 2. Accumulated mass of nitrate in drainage (kg NO3–N ha–1) during the period 1 May–1 Oct. 1997 in the different treatments. Irrigation started on 12 June 1997 (first arrow) and sidedress nitrogen was applied on 20 June 1997 (second arrow). See Table 2 for treatment descriptions.

 
The high drainage nitrate concentrations and loads during the first irrigations are attributed to high soil nitrate concentrations provoked by the applied fertilizers coupled to minimal crop nitrogen uptake in this period. In this experiment, LF was maintained constant along the crop cycle. However, it has to be considered that in surface-irrigated plots the first irrigation is the most inefficient due to the higher infiltration rates of the new tilled soil (Walker and Skogerboe, 1987). Thus, in surface-irrigated environments the application of fertilizer N should be matched to the crop N needs to control soil nitrate concentration and avoid excessive nitrate leaching (Zebarth et al., 1996). Therefore, although the amount of available nitrogen in PS2 is considered optimal for the yields obtained, nitrate concentrations in the leachate during the early stages of corn growth were high due to the low irrigation efficiencies. A better strategy of PS application would be that of treatment PS1 (i.e., lower doses before sowing complemented with mineral fertilization at sidedress). An alternative would be the application of PS at sidedress, which has not been analyzed in this work.

For the low irrigation efficiency treatments (target LF = 0.4) the highest average drainage NO3–N concentration (Table 3) was measured in Treatment PS3 (48.5 mg L–1) where the highest amount of PS was applied. Treatment PS3 also had the highest nitrate load in drainage (313 kg N ha–1). Drainage nitrate concentrations and loads consistently followed the amount of N applied in each treatment (Fig. 3) . A significant linear relation (p < 0.05) was established between amounts of inorganic nitrogen applied and nitrate loads and concentrations in drainage (Fig. 3). The fitted regression lines show increases of 4.6 kg NO3–N ha–1 in load and 0.69 mg NO3–N L–1 in concentration for each 10 kg N ha–1 increase in the amount of N applied, over the minimum of 275 kg N ha–1.


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  		Table 3. Flow weighted average nitrate concentration and nitrate load in drainage during the period 1 May–1 Oct. 1997 and nitrogen-use efficiency indexes for pig slurry (PS) treatments.

 


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  		Fig. 3. Nitrate concentration and load in drainage versus amount of inorganic N applied for high leaching fraction (LF) treatments.

 
The increase of nitrate leached in this irrigated environment (0.46 kg NO3–N ha–1 per unit increase of N fertilizer) is higher than the corresponding increases obtained in other rain-fed corn systems with mineral fertilizers. Sogbedji et al. (2000) found an average increase of 4.8 kg NO3–N ha–1 in the load of nitrate leached for 34 kg N ha –1 additionally applied over the optimum of 100 kg N ha–1 for two different soils and during two crop seasons. Jaynes et al. (2001) found average increases of 2.4 kg NO3–N ha–1 for each 10 kg of N applied over the economic optimum nitrogen fertilizer rate (EONR) during a two-year experiment. Similarly, for a second-year corn following alfalfa with an without manure applied to first-year corn, Andraski et al. (2000) found increases of 2.4 kg NO3–N ha–1 for each 10 kg of N applied over the EONR.

In contrast, the concentration increase due to additional N fertilizer application over the estimated optimum rates (0.069 mg NO3–N L–1 per unit increase of N fertilizer) was much lower than the corresponding increases obtained in the above-mentioned corn rain-fed systems. Sogbedji et al. (2000) in their experiment found average increases of 0.16 mg NO3–N L–1 per unit increase of N fertilizer over the optimum and Andraski et al. (2000) 0.15 mg NO3–N L–1 for each kg of N applied over the EONR.

In this experiment, the treatments with low irrigation efficiencies caused high losses in nitrate loads due to high drainage volumes, but nitrate concentrations did not increase as much as in rain-fed areas when the PS doses were increased, due to the diluting effects derived from the high volumes of applied irrigation water.

For the same N rate, the decrease of leaching fraction (PS1, target LF = 0.4 to PS1HE, target LF = 0.1) did not reflect in a significant increase of leachate nitrate concentration, but the amount of nitrate leached decreased by 65% (Table 3). Thus, increased irrigation efficiencies will decrease the mass of nitrate exported during the crop cycle. However, it has to be considered that high irrigation efficiency could induce high nitrate concentrations in the soil over a long time period.

The standard for nitrate in water sources is generally regulated as maximum allowable concentrations (European Union, 1991). However, it is important to emphasize that the mass of nitrate leached is the key variable when evaluating nitrate pollution in the receiving water bodies (Jaynes et al., 1999; Stites and Kraft, 2001; Cavero et al., 2003). A singular exception would occur when drainage from agricultural fields is the sole aquifer recharge. Thus, improvement of low efficiency irrigation systems, in addition to water conservation, in general, will produce desired improvements in nitrate water quality, although drainage nitrate concentrations could increase.

Nitrogen Budget and Nitrogen-Use Efficiency
The components of the N budget during the period 15 Apr.–1 Oct. 1997 are presented in Table 4. Unaccounted N was negative and significantly different than zero, indicating net nitrogen losses from the system, in all treatments. The losses are in the range found by Daudén and Quílez (2004) for similar PS doses in the same climatic conditions and are believed to be due to volatilization and immobilization and fixation of ammonium slurry (Daudén and Quílez, 2004). Losses were significantly higher in the PS3 treatment than in the rest of treatments. It has to be considered that the higher the total input of mineral N to the soil, the higher the proportion that is lost to the environment regardless of the source of N (Scholefield et al., 1991).


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  		Table 4. Nitrogen budget components for pig slurry (PS) treatments during the period 15 Apr.–1 Oct. 1997.

 
The efficiencies in the use of nitrogen and nitrate leaching among treatments were compared by means of three indexes: (i) the ratio of N uptake (aboveground matter) to applied fertilizer (RNUF), (ii) the nitrate leaching coefficient (NLC) or ratio between leached N and applied fertilizer N, and (iii) the grain yield per unit NO3–N leached (NUEL).

For the same target LF (LF = 0.4), RNUF increased with decreasing available N applied (Fig. 4) , indicating that the efficiency in the use of nitrogen decreases when the available N fertilizer rates increase above the optimum. Nitrate leaching accounted for between 10 and 34% of the applied N (Table 3), and the losses increased with increases in the rate of available N applied (Fig. 4). The NUEL ranged between 642 kg per kg of NO3–N leached and 79 kg per kg of NO3–N leached (PS3) and also decreased when the amount of available N increased.



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  		Fig. 4. Nitrogen use efficiency indexes, N in aboveground biomass per unit N applied as fertilizer (RNUF), nitrate leaching per unit N applied as fertilizer (NLC), and grain yield per unit NO3–N leached (NUEL) versus the amount of available N applied for the high leaching fraction (LF) treatments. *Significant at the 0.05 probability level. **Significant at the 0.01 probability level.

 
No significant differences were found in RNUF between PS1 (LF = 0.37) and PS1HE (LF = 0.16), which indicates that in this experiment leaching fraction did not affect the efficiency in the absorption of the N applied (Table 3). However, increased irrigation efficiency decreased nitrate losses from 12% (PS1, LF = 0.37) to 4% (PS1HE, LF = 0.16) of the nitrogen applied (Table 3). The value obtained for the low leaching fraction (PS1HE) was similar to values by Cavero et al. (2003) in a sprinkler-irrigated catchment of the Ebro River basin. Considering the importance of the N leaching environmental effect, it is important to note that the NUEL index in the PS1HE treatment (LF = 0.1) was three times greater than that in the PS1 treatment (LF = 0.4).


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The low and moderate PS rates were able to completely cover the N needs of irrigated corn and to obtain optimal yields in this Mediterranean environment. However, the PS rate above the N crop needs (200 Mg ha–1, PS3) did not increase corn yield. In contrast, the high PS rate produced the highest risk of environmental pollution to water resources due to higher nitrate concentrations and loads in drainage.

Although the moderate rate (PS2) was optimal for crop development, nitrate losses were high during the first irrigations. It is important in an irrigated environment to adapt N applications to crop extractions. Application of lower PS doses before sowing complemented with sidedressing N application (mineral or PS) would reduce nitrate losses in the first stages of crop development.

Improvement of irrigation did not affect crop yield but decreased the amount of nitrate leached. Surface irrigation, widely used in many areas of the world and in the Ebro River basin (Spain), generally has low irrigation efficiencies. To improve nitrogen-use efficiency and to diminish nitrate contamination (reduce exported nitrate loads) in these areas, good irrigation management is a key factor.


   ACKNOWLEDGMENTS
 
The authors thank Miguel Izquierdo and Jesus Gaudó for field management assistance. This study was funded by the Spanish Institute of Agricultural Research and Technology (INIA).


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 


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This Issue in Journal of Environmental Quality

JEQ 2004 33: 1947-1953. [Full Text]  




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