Abstract
In this paper we present results of a long-term crop rotation experiment established in 1971 in central Lithuania on morainic sandy loamy Epicalcari-Endohypogleyic Cambisols. The influence of regular fertilization with different NPK fertilizers in a crop rotation (winter wheat, sugar beet, spring barley, annual grasses and perennial grasses) and climatic conditions on the amount of N-compounds in lysimeter water (sampled at 40- and 80-cm depths) was investigated. Nitrate () concentration in lysimeter water depended mainly on the nitrate fertilizers application rate. Based on the 30-year mean (1976–2005), fertilization of agricultural crops with 112 kg N ha−1 increased nitrate concentration in lysimeter water at 40-cm depth by 67.1 mg l−1 to 112.1 mg l−1. An N-fertilization rate of 224 kg N ha−1 increased nitrate concentrations by 139.1 mg l−1 to 187.2 mg l−1. The effect of mineral fertilizers on ammonium (
) concentrations in lysimeter water was insignificant. Increases in the nitrogen concentration in lysimeter water in response to N-fertilization were more substantial when agricultural crops were not fertilized with phosphorus. Correlation between the nitrate concentration and applied amount of N-fertilizers was more statistically reliable when grain crops (r=0.65–0.67, n=74, p<0.001), sugar beet (r=0.63, n=27, p<0.001) and perennial grasses (r=0.40, n=59, p<0.01) were cultivated on the experimental field. Higher amounts of nitrate were leached when annual plants were cultivated, compared with perennial grasses. The concentration of NH4 and NO2 in lysimeter water was minimal and the influence of mineral fertilizers negligible.
Introduction
Although nitrogen is one of the most common elements in nature and the main one involved in plant nutrition, in excess it is harmful to the environment. Nitrogen and phosphorus compounds can cause eutrophication of water bodies. Nitrogen losses in the soil profile by leaching are one of the major environmental problems related to farming (Ibnoussina et al., Citation2006). Nitrogen (N) fertilizers are necessary for profitable cereal production but there is concern that excessive rates may have adverse effects on groundwater quality (Schepers et al., Citation1991). Unlike ammonium (), it is not absorbed by soil and not as easily taken up by plant roots, therefore it migrates into the soil profile. About 90–98% of nitrogen leached from soil is in nitrate form. Furthermore, part of the nitrate is converted into the more harmful form, nitrite (
).
The most important role influencing nitrogen leaching was the differing amounts of nitrogenous fertilizer applied (Brandi-Dohrn et al., Citation1997; Owens et al., Citation1999; Kuo et al., Citation2001; Ibnoussina et al., Citation2006). Nitrogen leaching depends not only on soil fertilization, but also soil cultivation, liming, crop type, soil genesis and texture, amount of leaching water, amount of N in soil, climatic conditions and soil coverage with plants (Thomas et al., Citation1992; Catt, Citation1993; Ezerinskas, Citation1993; Nearing et al., Citation1993; Sileika, Citation1996; Brandi-Dohrn et al., Citation1997, Rimselis et al., Citation1998; Meals & Budd, Citation1998; Cambardella et al., Citation1999; Goulding et al., Citation2000; Luo & Lindsey, Citation2005). Migration of elements and their compounds is strongly influenced by precipitation. Infiltration processes in soil are mainly influenced by the meteorological regime and soil texture (Tyla, Citation1995).
Intensive agriculture enhances nutrient leaching from soil (Jordan et al., Citation1997). Results of various experiments in different countries prove the possibility to minimize the environmental impact of intensive agriculture by selecting the most appropriate crop rotations with intermediate crops, where the soil is constantly covered with plants (Brandi-Dohrn et al., Citation1997; Torstensson, Citation1998). Swedish researchers estimated that N leaching could be reduced by 20 kg ha−1 if soil was covered by plants in late autumn and winter (Jakobsson, Citation1999). Nitrate-nitrogen may also leach in significant amounts during the winter and early spring periods, when plant growth and uptake of N is minimal (Owens, Citation1990). Many researchers have investigated means to reduce the potential of N loss from agricultural production systems, such as winter cover crops and lower fertilizer N rates (Staver & Brinsfield, Citation1990; Hubbard et al., Citation1991).
Data obtained from long-term experiments in Lithuania show that the concentration of ions in lysimeter water from different types of soil varied from 49.2 to 71.5 mg l−1, and average annual leaching of N was 31–33 kg ha−1. Nitrogen leaching depended on leachate volume, the amount of N fertilizers, soil texture and soil humus content. However, even in the light soils of eastern Lithuania, N losses through leaching did not exceed 10% of applied N (Vaicys et al., Citation1998).
It is known that anthropogenic activity (fertilizers, soil cultivation, crop rotation) and meteorological conditions influence pollution of the environment; thus, it is necessary to ascertain the different factors causing the nitrogen leaching.
The aim of the long-term lysimeter experiments (1976–2005) was to study in Lithuanian soils with different crop rotations the influence of NPK mineral fertilizer rates and ratios, N accumulated in crop yield, and meteorological conditions for leaching nitrogen compounds (,
,
) to the lysimeter water.
Materials and methods
A long-term fertilization trial was established on a morainic sandy loamy Epicalcari-Endohypogleyic Cambisol as early as 1971 (55°34′28.616887′′N, 23°45′1.34973′′E, according to WGS-84) (). The soil texture of a representative profile was studied. The Ap horizon is mainly sand (2.0–0.05 mm) fraction (54.7%) with lesser amounts of silt (0.05–0.002 mm, 31.2%) and clay (<0.002 mm, 14.1%) fractions.
Figure 1. Place of research.
The average amount of precipitation in Lithuania during 1929–2005 was 670 mm. In the period of the experiments (1976–2005) it was from 416 to 780 mm. Average annual temperature was 6.0°C. Ap horizon soil – pHCaCl2 7.1 – with low exchangeable soil acidity (1 M KCl, 0.3 mmol kg−1), excessive amount of exchangeable cations (136.7 mmol kg−1, estimation based on 1 M acetate ammonium extraction), average humus content (2.2%, Tyurin method) and Ntot (0.17%, Kjeldahl method), low phosphorus content (57 mg kg−1) and average amounts of potassium (109 mg kg−1, Egner-Riehm-Domingo method based on ammonium lactate extraction). Subsoil (Bw) horizons were slightly alkaline, containing more mobile P and less mobile K than the Ap horizon.
N fertilization rate for cereals and annual grasses was 90, 180 kg ha−1 (+PK – 90, 180 kg ha−1), for sugar beet 120, 240 kg ha−1 (+PK – 120, 240 kg ha−1), for perennial grasses 157.5, 315 kg ha−1 (+PK – 90, 180 kg ha−1). Average rates in the rotation for N fertilizers were 112 and 228, for P and K 95 and 190 kg ha−1, respectively. Ammonium nitrate, superphosphate and potassium chloride fertilizers were used. P and K fertilizer rates and the P and K content in soil are presented as oxides (P2O5, K2O).
The following crop rotation was applied: winter wheat (1974, 1980, 1983, 1987, 1994, 1996, 1998 and 2002), sugar beet (1971, 1975, 1981, 1984, 1999 and 2003), spring barley (1972, 1985, 1988, 1995, 2000 and 2004), annual grasses (1973, 1976, 1982, 1986, 1997, 2001 and 2005) and perennial grasses in 1977–1979 and 1989–1993.
Lysimeters of the Silova type (Silova, Citation1955) were installed in 1976 at 40-cm depth in test plots of nine variants: N0P0K0; N0P95K95; N112P0K95, N112P95K0; N112P95K95; N0P190K190; N224P0K190; N224P190K0; N224P190K190, and at 80-cm depth in test plots of four variants: N0P0K0; N112P95K95; N0P190K190; N228P192K192.
The hydrothermal coefficient (HTC) (by Selianinov) was used for evaluation of meteorological conditions and was calculated using the formula according to the scale proposed by Czech scientists (Coufal, Citation1987).
Where Σp is the sum of precipitation in V, VI, VII, VIII and IX months, when the temperature is >10°C, Σt = sum of active (>10°C) air temperatures of the same period.
During the period of experiments an average drought (HTC 0.68 and 0.57) was recorded in 1992 and 2002; slight drought (HTC 0.8–0.9) in 1982, 1983, 1991, 1999 and 2003; normally humid season (HTC 1.0–1.5) in 1976, 1977, 1978, 1979, 1984, 1985, 1986, 1988, 1989, 1990, 1994, 1995, 1996, 1997, 2001, 2004 and 2005; humid season (HTC 1.6–1.77) in 1981, 1987, 1993, 1998 and 2000; and excessively humid season (HTC 2.24) in 1980.
Lysimeter water samples were taken in spring before fertilization and sowing and in autumn after harvesting. Analyses of N compounds were carried out in the laboratories of the Agrochemical Research Centre of the Lithuanian Institute of Agriculture, using a spectrometric method: NO3 – using sulphosalicylic acid, NH4 – using hypochlorite, NO2 – using 4-aminobenzenesulphonamide. Dispersion of statistical data obtained during the experiments is characterized using standard deviations and inter-relations using correlation and regression analyses. Data corresponding to p<0.05 are marked with r* (correlation coefficient), p<0.01 with r** and p<0.001 with r*** (Clewer & Scarisbrick, Citation2001). Statistical analysis was performed using the Microsoft Excel program.
Results
In our experiments taking the 1976–2005 mean, an N fertilization rate of 112 kg N ha−1 (+PK) increased nitrate concentration by 67.1 mg l−1 to 112.1 mg l−1 in water from lysimeters installed at 40-cm depth. N fertilization at 224 kg ha−1 increased the concentration of nitrates by 139.9 mg l−1 to 187.2 mg l−1 (). An even higher nitrate concentration increase (112.4 and 256.4 mg l−1) was recorded in test plots where agricultural crops were not fertilized with PK. Only potassium fertilizers had a lesser stabilizing effect on nitrate leaching from the upper soil layers.
Table I. Influence of mineral fertilization on N compound concentrations (mg l−1) in lysimeter water.
Mean nitrate concentration in water of lysimeters installed at 80-cm depth was 1.2 times less than in the lysimeter water at 40-cm depth. Dispersion of concentration values in lysimeter water was statistically significant. The
concentration in lysimeter water at 40-cm depth was up to 174 mg l−1 in the unfertilized test plots; in the test plots fertilized with N112P95K95 and N224P190K190 rates annually,
concentration was up to 327 and 624 mg l−1, respectively.
The concentration in the tested samples of lysimeter water was low, dispersion was minimal and the influence of mineral fertilizers negligible. At 40-cm depth in the unfertilized test plot, the mean ammonium concentration was 0.70 mg l−1. Under the influence of different combinations of lower rates of N, P and K fertilization, ammonium concentration was in the range 0.48–0.62 mg l−1, the higher rates 0.50–0.75 mg l−1, and at 80-cm depth 0.81 and 0.82 mg l−1, respectively.
The concentration of in lysimeter water was even less than the concentration of ammonium and the influence of N-fertilization was insignificant. The average
concentration in lysimeters at 40-cm depth in the unfertilized test plots was 0.29 mg l−1, at 80 cm depth 0.08 mg l−1; in the test plots fertilized with lower rates of fertilizers 0.11–0.35 and 0.07 mg l−1, respectively, higher rates 0.11–0.42 and 0.08 mg l−1. Somewhat higher nitrite concentrations were recorded after growing annual grasses in place of cereals, and after the summer and autumn seasons compared to the winter-spring season.
Dispersion of nitrate concentration was caused by several factors, such as cultivation plants, vegetation period and climatic conditions ( and , and ).
Figure 2. Annual nitrate () concentration in relation to fertilizer rates and meteorological conditions.
Figure 3. Variation dynamics of nitrate () concentration in lysimeter water (at 40-cm depth).
Table II. Nitrate concentrations in lysimeter water as affected by cultivation of different crops.
Table III. Nitrate concentrations in lysimeter water during separate seasons.
More nitrate was leached in years when winter wheat, sugar beet, barley and annual grass crops were cultivated rather than perennial grasses, especially in humid seasons. Leached amounts varied seasonally.
Multinomial regression analysis gave a fairly reliable correlation between N compound concentrations in lysimeter water and NPK fertilizers. After fertilization with various rates of NPK fertilizers, the correlations between application rate and nitrate leaching were significant for all agricultural crops (r=0.67–0.89, n=161, p<0.001). This was especially the case for barley (r=0.89, n=37, p<0.001) and annual grasses (r=0.79, n=31, p<0.001) ().
Table IV. Relation of nitrate (
) concentrations in lysimeter water to NPK fertilization.
The concentration of mineral N in lysimeter water depended mostly on the amount of N fertilizers applied (r=0.40–0.67); correlation was strongest (r=0.67, n=45, p<0.001) when barley was cultivated, and weakest (r=0.40, n=59, p<0.01) under perennial grasses (). Correlation between nitrate leaching and N accumulated in the yield was highest where barley was cultivated (r=0.81, n=6, p>0.05), followed by perennial grasses (r=0.76, n=8, p<0.05) and sugar beet (r=0.71, n=6, p>0.05).
Table V. Leaching of nitrates (mg l−1/year) in relation to selected influencing factors (x).
The relation between the nitrate concentration in lysimeter water and climatic conditions during the growing season was statistically significant when sugar beet (r=0.54, n=26, p>0.01) and annual grasses (r=0.41, n=38, p>0.05) crops were cultivated ().
Table VI. Mineral nitrogen (Nmin) in water as affected by climatic conditions.
Discussion
Many authors’ research confirms that the nitrogen pollution of groundwater increases, generally, with the amount of nitrogenous fertilizer applied (Brandi-Dohrn et al., Citation1997; Owens et al., Citation1999; Kuo et al., Citation2001; Ibnoussina et al., Citation2006). Non-controllable factors such as precipitation and mineralization of soil organic matter have a tremendous effect on drainage losses, nitrate concentrations, and nitrate loadings in subsurface drainage water. Cropping system and nutrient management inputs are controllable factors that have a varying influence on nitrate losses. Row crops leach substantially greater amounts of nitrate compared with perennial crops (Gyles et al., Citation2001).
In our research the concentration of nitrate (NO3) in the lysimeter water depends mainly on the nitrogen fertilization rate. According to the calculated means of the data collected during the period of 30 years, when the crops were fertilized with an average (112 kg ha−1) rate of nitrogen with a background of phosphorus and potassium fertilizers, the concentration of nitrate in the water from 40-cm depth compared with treatment without nitrogen fertilizers increased 2.5 times. After fertilizing with twice the rate of nitrogen, the concentration of nitrate in the water increased 5.2 times. The highest leaching level of N compounds was recorded in the variants in which the test plot was fertilized with N and K (without P) and N and P (without K). In the variant in which P fertilizers were not applied, the concentration of N compounds was 2.9 times higher (compared to the unfertilized variant) when fertilization rates were lower, and 5.6 times higher when fertilization rates were higher. In the variant where K fertilizers were not applied, the concentration of N compounds was 1.4 and 4.5 times higher, respectively. Mineral N concentrations in the lysimeter water of the unfertilized plots and the plots fertilized only with P or K were similar.
Simmelsgaard (Citation1998) reported that the most important factor influencing leaching was the crop type. Grass and barley undersown with grass showed low rates of leaching (17–24 kg/ha/year). Winter cereal following a grass crop, beets, and winter cereals following cereals and an autumn sown catch crop following cereals showed medium rates of leaching (36–46 kg/ha/year). In our experiment the concentration of nitrates in lysimeter water was comparatively high when the experimental field was growing sugar beet, fertilized with high rates of N and not fertilized with any P and K. The least nitrate was leached into subsoil water when perennial grasses were grown.
However, grass swards themselves are efficient at taking up nitrogen (N) from soil; the risk of leaching is increased where N input exceeds the sward's capacity to utilize the available N (Cuttle et al., Citation2001).
The concentration of nitrates in lysimeter water was comparatively high when the experimental field was growing sugar beet, fertilized with high rates of N and not fertilized with any P and K. The least nitrate was leached into subsoil water when perennial grasses were grown. Even under conditions of high N fertilization rates (315 kg N ha−1), the concentration was 1.04–1.5 times less than under the sugar beet crop. The nitrate concentrations in lysimeter water taken from the test plots of corresponding fertilization variants of different crops – cereals (winter wheat and spring barley) and annual grasses – were very similar. Concentrations were somewhat lower than under the sugar beet crop, but higher than under perennial grasses. According to the data of the whole experimental period, long-term annual fertilization with N increases nitrate leaching.
The dependence of leaching of N compounds on various factors (different fertilizer types, amount of N accumulated in the agricultural crop and climatic conditions) was evaluated using correlation and regression criteria. The correlation between leaching and N fertilization was significant when barley, sugar beet, winter wheat and annual grasses crops were grown (r=0.63–0.67, n=101, p<0.001). Here the determination coefficients show 40–42% influence of N fertilizers. The dependence of nitrate leaching on P and K fertilizers was much weaker: r=0.18–0.39, n=211, p>0.05; and r=0.19–0.33, n=193, p>0.05, respectively.
Correlation between nitrate leaching and N accumulated in the yield was highest where barley was cultivated, followed by perennial grasses and sugar beet.
The relation between the nitrate concentration in lysimeter water and climatic conditions (according to HTC) and between amount of precipitation and temperature during the growing season was statistically significant when sugar beet, annual grasses and perennial grasses crops were cultivated.
The effects of weather on nitrate leaching are not simple since the former (e.g. temperature, rainfall) affect the N-cycle by influencing mineralization, nitrification and soil aerobicity (Jarvis et al., Citation1996; Hooda et al., Citation1998). In warm summers, nitrate leaching losses are potentially greater compared to cool summers. Our long-term experiment established that in the humid 1980,1987,1993, and 1998 years nitrate leaching was greater compared to other years.
Related Research Data
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