Published in Agron. J. 96:839-844 (2004).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
SOIL FERTILITY
Effects of Chloride Fertilization on Wheat (Triticum aestivum L.) Productivity in the Sandy Pampas Region, Argentina
M. Díaz-Zorita*,a,
G. A. Duarteb and
M. Barracoc
a Dep. of Plant Prod., Faculty of Agron., Univ. of Buenos Aires, 1417, Av. San Martín 4457, Buenos Aires, Argentina, and Nitragin Argentina S.A., Calle 10 y 11, Parque Industrial Pilar, 1629, Pilar, Buenos Aires, Argentina
b AACREA M. Cachau 189, 6236, América, Buenos Aires, Argentina
c EEA INTA General Villegas, CC 153, 6230, General Villegas, Buenos Aires, Argentina
* Corresponding author (mdzorita{at}speedy.com.ar).
Received for publication November 8, 2003.
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ABSTRACT
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The soils from the sandy Pampas region (Argentina) are coarse-textured Mollisols with high to very high extractable K levels. However, in several KCl fertilization field trials, wheat (Triticum aestivum L.) grain yield and alfalfa (Medicago sativa L.) dry matter production increments have been reported. Our objective was to determine the contribution of Cl– fertilization on dryland spring wheat productivity. The study was performed during the 2001 and the 2002 growing seasons on 10 experimental sites establishing 14 treatments in completely randomized blocks with four replications: Cl– fertilization rates (0, 23, 46, and 69 kg ha–1), Cl– fertilizer sources (KCl and NH4Cl), and crop disease control (with and without fungicide applications during stem elongation). Chloride fertilization increased grain yields in 50% of the sites independently of the fertilizer source and the fungicide treatments. Averaged over the 10 locations, the grain yield response to Cl– fertilization was of 253 kg ha–1, and it was mostly explained by a greater number of grains per square meter. Soil Cl– levels >13.2 mg kg–1 (0.0 to 0.2 m) were adequate for maximum grain yields. Foliar fungicide application also improved wheat grain production, enlarging the single weight of the grains. In the absence of water, N, P, and S deficiencies, the fertilization with 23 to 46 kg ha–1 of Cl––containing fertilizers after the emergence of wheat crops is a recommended practice for achieving high-yielding crops in the sandy Pampas region of Argentina.
Abbreviations: CFR, chloride fertilization rate • RGY, relative wheat grain yield • SECl, soil extractable chloride levels in the 0.0- to 0.2-m layer
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INTRODUCTION
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THE SOILS IN THE PAMPAS region of Argentina present high to very high extractable K levels (Sillanpää, 1982; Hall et al., 1992). However, several field essays performed in this region have shown positive responses in alfalfa dry matter production and wheat grain yields after KCl fertilization, generally in combination with N, P, and S fertilization practices (Conti et al., 1997; Melgar et al., 2000; Duarte et al., 2001; Díaz-Zorita and Duarte, 2002). For example, Duarte et al. (2001) in the sandy Pampas reported a mean wheat grain yield increment of 28%, approximately 300 kg ha–1, after fertilizing with 50 to 100 kg ha–1 of KCl under nonlimiting N and P levels. The grain yield response was attributed to both grain number and single grain weight enhancement after KCl fertilization.
Chlorine, basically in the form of chlorides (Cl–), participates in several physiological processes in the plants (e.g., osmotic regulation, diseases suppression, etc.), and it is one of the essential elements required for a normal development and growth of the crops (Havlin et al., 1999; Kafkafi and Xu, 2002). Several studies performed in the Great Plains and the Pacific Northwest regions of the USA suggest that Cl– fertilization practices, basically applied in the form of KCl, enlarges the productivity of wheat and other crops (Engel et al., 1997; Grant et al., 2003; Lamond, 2003). In general, the benefits of Cl– fertilization have been attributed to lowering the negative effects of diseases during the development of the crops (Christensen et al., 1981; Engel and Grey, 1991; Miller and Jungman, 1998). It is not the sole reason for the benefits—yield response to Cl– is more general than disease reduction (Fixen et al., 1986a; Engel et al., 1994; Grant et al., 2003). Chloride fertilization eliminated or prevented the occurrence of a leaf spot syndrome that is not disease related (Engel et al., 1997). Chloride may also increase wheat grain yields with an enhanced NH4 supply attributed to lower leaf osmotic potentials, delayed nitrification in the soil, and inhibition of take-all root rot (Gaeumannomyces graminis) (Christensen and Brett, 1985; Koening and Pan, 1996). However, other studies performed in the same region indicate that Cl– fertilization does not increase significantly wheat grain yields (Mohr et al., 1992; Carr et al., 2001).
Wheat is one of the most economically important crops in the semiarid Pampas region of Argentina. The area sown annually to wheat is about 1000000 ha, which represents more than 10% of the total agricultural area of the region. Foliar diseases, i.e., Septoria leaf blotch (Septoria tritici), may be responsible for up to 10% of yield losses every year (Galich et al., 1986). Foliage-applied fungicides are generally applied during stem elongation or delayed until ear emergence.
The sandy Pampas region is located far from the ocean or other natural Cl– sources; hence, Cl– deposition from atmosphere is likely to be low (Turner and Kelly, 1973). The soils of this region are coarse textured and highly permeable, and Cl– leaching is likely due to its high water solubility and low sorption to soil particles. Furthermore, the use of KCl fertilization practices for crop production in the Pampas is low due the high soil K test levels. These factors make it feasible that crop responses to KCl, particularly for wheat, may be a result of Cl– deficiencies. Our objective was (i) to determine the contribution of Cl– fertilization on dryland spring wheat grain production and yield components and (ii) to develop a Cl– fertilization recommendation for spring wheat in this region.
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MATERIALS AND METHODS
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The study was performed during the 2001 and the 2002 wheat-growing seasons in 10 experimental sites located in the northwestern part of Buenos Aires province lying within the sandy Pampas region on sandy to loamy sand Molisols. General description of field study sites and main characteristics of the soil types are presented in Table 1. Composite soil samples from the 0.0- to 0.2-, 0.2- to 0.4-, and 0.4- to 0.6-m layers were taken at seeding for the determination of soil extractable Cl– contents (Adriano and Doner, 1982).
During the second week of July, when the crops showed the main shoot and the first tiller developed, growing stage 21 (Zadoks et al., 1974), the following seven fertilization treatments were broadcasted on the soil surface: (i) control without Cl– fertilization, (ii) 50 kg ha–1 of KCl, (iii) 100 kg ha–1 of KCl, (iv) 150 kg ha–1 of KCl, (v) 36 kg ha–1 of NH4Cl, (vi) 72 kg ha–1 of NH4Cl, and (vii) 108 kg ha–1 of NH4Cl. The treatments ii, iii, and iv provided 23, 46, and 69 kg ha–1 of Cl– with K, respectively. The treatments v, vi, and vii provided the same Cl– rates in the absence of K fertilization. In all of the treatments, urea fertilization was performed to provide the same N supply as that supplied by the highest NH4Cl fertilization rate (i.e., 28 kg ha–1). When the crops presented the fifth node detectable, Growing Stage 35 (Zadoks et al., 1974), each of the plots was subdivided, and then fungicides (epoxiconazole {rel-1-[[(2R,3S)-3-(2-chlorophenyl)-2-(4-fluorophenyl)oxiranyl]methyl]-1H-1,2,4-triazole} 0.125 + carbendazim [methyl 1H-benzimidazol-2-ylcarbamate] 0.125) were foliar-applied at 1 L ha–1 rate. Half of the plots were kept without the application of the fungicide treatment. In each location, the experimental design was in randomized complete blocks with a split-plot arrangement, with foliar fungicide as main plots and fertilizer treatments as subplots with four replicates and plots of 10 m2.
Crop and soil management practices were similar in the 10 studied sites. In all cases, soybean [Glycine max (L.) Merrill] or sunflower (Helianthus annuus L.) were the preceding crops, and the fallow period was started in late May. Spring wheat crops of intermediate maturity group were sown within the last week of June and the first 2 wk of July under no-tillage practices and fertilized with 50 to 70 kg ha–1 of diamonic phosphate (DAP, 18–46–0). After the emergence, the crops were fertilized with 75 to 125 kg ha–1 of urea (46–0–0) to achieve at least 110 kg ha–1 of available N (N soil at planting + N fertilizer) and with 100 kg ha–1 of ammonium sulfate (21–0–0–23S). Both urea and ammonium sulfate were broadcasted while DAP was banded into the soil.
Each year, during the first week of December, crop grain production and other components of the yield were determined at physiological maturity, growing stage 91 (Zadoks et al., 1974). Duplicate samples (1 m2) were hand-harvested from the four central rows of each plot to determine grain yield, plant population, and spikes density. The weight of single grains was also determined from the weight of 300 grains per samples. The grain weight was adjusted to 0.14 g g–1 of moisture content. From the average of grains per spike in 20 consecutive spikes in each plot, the number of grains per spike was determined.
A three-factor [fertilizer source, Cl– fertilization rate (CFR), and fungicide treatment] analysis of the variance and protected least significant difference (LSD) test were performed for each site, combining all the experimental sites. Correlation and regression analyses were utilized among crop productivity parameters, grain yield response to Cl– fertilization, and soil properties (Analytical Software, 2000).
Relative wheat grain yield (RGY) to the maximum grain yield (YM) in each experimental site was calculated using the following equation,
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where Yo is the mean wheat grain yield of each Cl– fertilization treatment averaged over the two Cl– fertilizer sources and the two fungicide treatments. Both Yo and YM are expressed in units of kg ha–1.
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RESULTS
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2001 Growing Season
Wheat grain production varied between 1049 and 6205 kg ha–1, showing significant differences after fungicide and Cl– fertilization treatments independently of the Cl– fertilization source (Tables 1 and 2). Both the number of grains per square meter and the single grain weight were positively correlated with the grain yields, r = 0.96 (p < 0.01) and r = 0.86 (p < 0.01), respectively.
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Table 2. Summary of ANOVA table and mean wheat grain yields (averaged over two Cl– fertilizer sources and two fungicide treatments) on 10 experimental sites from the sandy Pampas region of Argentina during the 2001 and 2002 growing seasons.
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In the three studied sites, significant yield differences due to CFRs were observed without relevant effects of the type of fertilizer (Table 2). The fungicide protection treatment significantly enhanced the wheat production in two of the experimental sites (Table 2). In general, there were not significant interactions between the three studied factors on the wheat grain yields (Table 2).
Averaged over the three studied sites, Cl– fertilization and fungicide treatments also modified the final number of grains and its single weight (Table 3). No significant effects of the Cl– fertilizer source on both yield components and grain production were detected. Although the number of spikes per square meter was also positively correlated with the grain yields (r = 0.54, p < 0.01), the available information was not enough for detecting significant treatments effects on this crop variable (Table 3).
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Table 3. Summary of ANOVA table for the wheat yield components according to fungicide and Cl– fertilization treatments on 10 experimental sites from the sandy Pampas region of Argentina during the 2001 and 2002 growing season.
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The mean wheat grain response to the fungicide treatments was of 289 kg ha–1. This behavior was basically explained by the increment in single grain weight (Table 4). On the other hand, Cl– fertilization enhanced wheat grain production because of a greater number of grains per square meter (Table 5). The mean grain yield response to CFR (kg ha–1) described a diminishing returns model, and from the fitted quadratic equation [RGY (%) = –0.0058 x CFR2 + 0.6178 x CFR + 81.429; R2 = 0.27, p < 0.10], it was estimated that the optimum agronomic CFR was achieved applying 53.2 kg ha–1. In terms of KCl or NH4Cl fertilizers, the maximum wheat grain production was obtained fertilizing with 116 or 82 kg ha–1, respectively.
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Table 4. Mean foliar fungicide application effects on wheat productivity. Average of three experimental sites in 2001 and seven experimental sites in 2002 production seasons, four Cl– fertilization rates (0, 23, 46, and 69 kg ha–1), and two fertilizer sources (KCl and NH4Cl).
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Table 5. Mean Cl– fertilization rate effects on mean wheat productivity. Average of experimental sites (three in 2001 and seven in 2002 production seasons), two fungicide treatments (with and without application), and two fertilizer sources (KCl and NH4Cl).
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2002 Growing Season
The wheat grain yields varied between 1200 and 5874 kg ha–1, showing significant differences due to the fungicide treatments in most of the experimental sites (Table 2). Only in two of the essays did the Cl– fertilization treatments significantly enhance the wheat grain yields (Table 2). There were no significant differences in grain production due to the Cl– sources, and the interactions among the three studied factors were not significant (Table 2). Both the number of grains per square meter and the single grain weight were positively correlated with the grain yields, r = 0.97 (p < 0.01) and r = 0.46 (p < 0.01), respectively.
Averaged over the seven experimental sites, the Cl– fertilization treatments improved the number of grains per square meter (p < 0.20) while the foliar application of fungicides favored a greater single weight of the grains (p < 0.06, Table 3). The mean grain production response to fungicide treatments was increased in approximately 85 kg ha–1, equivalent to a 2% increment over the untreated plots (Table 4).
In general, the treatment with the application of 46 kg ha–1 of Cl– showed more grain yield than the untreated plots (Table 2) without differences between the fertilizers sources or the other CFRs (Table 2). The grain yield response to CFR described a diminishing returns model, and from the fitted quadratic equation [RGY (%) = –0.0031 x CFR2 + 0.2809 x CFR + 92.172; R2 = 0.2205, p < 0.10], it was observed that the optimum agronomic CFR was achieved applying 45.3 kg ha–1. In terms of KCl or NH4Cl fertilizers, the maximum wheat grain production was obtained fertilizing with 98 or 70 kg ha–1, respectively.
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DISCUSSION
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We observed that in 50% of the trials, Cl– fertilization increased wheat grain yields independently of the fertilizer type and the application of fungicides protecting reproductive growing stages (Table 2). The lack of significant differences between Cl– sources (KCl or NH4Cl) suggests that the wheat productivity responses to Cl– fertilization could be mostly attributed to direct Cl– effects of this ion on the behavior of the crops. Chloride crop nutrition improves the sanitary status of the crops under different environmental and production conditions (Fixen et al., 1986a, 1986b). The mean responses to Cl– fertilization treatments observed in our study are in agreement with the results described for winter wheat crops in the state of Montana (USA) after fertilizing with 22.5 to 90.0 kg ha–1 of Cl– (Engel and Grey, 1991). Similar conclusions were achieved based on eight field essays performed in Molisols from the central part of the Pampas region (Melgar et al., 2001).
Because the grain yield in wheat, and other crops, results from the product between the number of grains per surface unit and the single weight of the grains (Egli, 1998), both yield components can help us to understand when the applied treatments induced changes in the behavior of the crop. In our study, the application of Cl– promotes a greater number of grains per square meter, suggesting that the treatment effectively improved wheat growth during early development stages (Satorre and Slafer, 1999). However, in both growing seasons, and based on visual observations of the crops during the early growing stages, there were no differences in the incidence of foliar diseases (i.e., leaf blights caused by Septoria nodurum and Drechslera tritici-repentis) between fertilization treatments. However, in both seasons, scab (Fusarium graminearum)-infested wheat heads were observed in most of the plots without foliar fungicide application. The protection of the crops using fungicides promoted a better growth of the plants during reproductive stages, improving the single weight of the grains and the grain production.
The RGY of the Cl– unfertilized treatments decreased when increasing the soil extractable Cl– levels in the 0.0- to 0.2-m layer (SECl) following a diminishing returns model [RGY (%) = –0.605 x SECl2 + 15.977 x SECl – 6.448; R2 = 0.62, p < 0.05; Fig. 1]
. Although the SECl values were positively correlated with the Cl– levels from deeper layers [SECl (0.2 to 0.4 m) (mg kg–1) = –2.04 + 1.00SECl; r = 0.90, p < 0.01; SECl (0.4 to 0.6 m) (mg kg–1) = –0.72 + 0.84SECl; r = 0.74, p < 0.01], the explanation in the variability of the RGY based on the soil extractable Cl– contents in the 0.0- to 0.4-m layer [RGY (%) = –0.404x2 + 10.633x + 28.071; R2 = 0.419, p < 0.05] or the 0.0- to 0.6-m layer [RGY (%) = –0.420x2 + 10.544x + 31.638; R2 = 0.368, p < 0.05] decreased.
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Fig. 1. Effect of soil extractable Cl– content (0.0- to 0.2-m layer) on relative grain yield of wheat in 10 sites from the sandy Pampas region fertilized with Cl–. Each point is the average of two Cl– fertilizer sources (KCl and NH4Cl) and two foliar fungicide treatments. The solid line shows the quadratic fitted relationship between variables for the Cl– unfertilized treatments.
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Based on the fitted quadratic equation between SECl contents and RGY, it was estimated that the maximum agronomic wheat yields, relative to the maximum grain production after Cl– fertilization, was achieved in soils with at least 13.2 mg kg–1 of SECl. Ninety and 80% of the maximum grain yields were achieved in soils with 9.3 and 7.6 mg kg–1 of SECl contents, respectively. Assuming a soil bulk density value of 1.2 Mg m–3, soil Cl– contents (0.0 to 0.2 m) greater than 32 or 22 kg ha–1 were adequate for maximum or 90% of the maximum yields, respectively. These values are greater than the critical values estimated in other regions. For example, responses to Cl– fertilization in Kansas appear to be most likely when soil Cl– levels (0.0 to 60 m) are less than 22 kg ha–1 or 4 mg kg–1 (Lamond et al., 1999; Lamond and Leikam, 2002). Researchers from eastern South Dakota reported that soil Cl– levels (0.0 to 0.6 m) greater than 43.5 kg ha–1 were adequate for near-maximum wheat grain yields (Fixen et al., 1986a). Cultivar selection and other factors such SECl distribution relative to root distribution, foliar and root disease pressure, and the timing of moisture or temperature stress affect grain yield response to applications of Cl– in wheat (Fixen, 1993) and could partially explain the differences between our results and those reported by other researchers. Furthermore, part of the fertilizer Cl– could have leached from the profile during the growing season. In our study, soil extractable Cl– contents were negatively correlated with the sand contents of the soils (data not shown). In agreement with this result, greater grain yield responses to Cl– fertilization were observed on sites with soils classified as Entic Hapludolls (Table 1).
Based on the mean crop response to fungicide treatments, it is assumed that in the 2001 growing season, a greater disease pressure effect occurred compared with the following season (Table 4). The amount of rainfall during the vegetative growing stages of the crops (July to September) was greater in 2001 than in 2002 (Table 1). This results suggest that the low proportion of sites with significant responses to Cl– fertilization practices during the 2002 production season could be explained because of a lower diseases pressure during the vegetative growing season.
Our results suggest that Cl– fertilization in inland sandy soils, although there were no visual differences in the incidence of foliar diseases, promotes a better growing environment during vegetative stages and contributes to an additive effect on grain production through a greater number of grains per unit area. This behavior is independent of the Cl– fertilizer source and complemented by diseases' crop protection during reproductive growing stages based on foliar fungicide treatments. The variability in the responses between experimental sites is partially attributed to differences in soil Cl– contents and other factors (e.g., wheat cultivar, diseases pressure during early growing stages, etc.).
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CONCLUSIONS
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In the absence of P, N, and S nutritional limitations, wheat grain production in the sandy Pampas region can be improved with the application of 23 or 46 kg ha–1 of Cl– broadcasted after the emergence of the crop independently of the fertilizer source (i.e., KCl or NH4Cl). On average over 10 experimental sites, the response to Cl– fertilization is 253 kg ha–1, approximately 7% of yield increment over the control without Cl– application. Chloride fertilization promoted better vegetative growing conditions, yielding a greater grain number per unit surface. The crop protection with the application of fungicides during early reproductive growing stages contributes to enhance the grain production without interfering with the response to Cl– fertilization.
Greater response is expected in sites with soil extractable Cl– levels lower than 13.2 mg kg–1 (0.0 to 0.2 m) and classified mostly as Entic Hapludolls with coarse surface textures. However, further research is required for adjusting the diagnosis of potentially Cl– deficient environments based on soil properties in combination with crop management practices (e.g., wheat cultivar, fungicide management practices, etc.).
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ACKNOWLEDGMENTS
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The financial support by INPOFOS Cono Sur, INTA General Villegas, and farmers from the América CREA group is greatly appreciated.
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ABSTRACT
INTRODUCTION
