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SOIL FERTILITY

Bread-Making Wheat and Soil Nitrate as Affected by Nitrogen Fertilization in Irrigated Mediterranean Conditions

Centre UdL-IRTA, Rovira Roure 177, 25198 Lleida, Spain

* Corresponding author (jaume.lloveras{at}irta.es)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Mediterranean areas are suitable for the production of high quality bread-making wheat (Triticum aestivum L.) because of the high temperatures during grain filling. Wheat quality is also influenced by variety and can be enhanced through the use of N fertilizer. However, N fertilization can increase residual soil NO^-₃ after harvest. The purpose of this study was to evaluate the effect of supplemental topdressed N fertilizer on quality and production of high quality bread-making wheat and on residual soil NO^-₃ under irrigated Mediterranean conditions. Field experiments were conducted at two sites during two growing seasons on Calcixeroclic Xerochrept soils of the Ebro Valley (Spain). Five N treatments (100, 200, and 300 kg N ha^-1 applied at the end of tillering and 150 or 250 kg N ha^-1 at the end of tillering plus 50 kg ha^-1 foliar-applied N at the end of the boot stage) were imposed on two cultivars. Topdressed N increased yields, when increasing from 100 kg N ha^-1 to higher rates only, in soils with low residual NO^-₃. However, N fertilization increased grain protein contents for all locations and years and bread quality parameters but with a greater effect in soils with low soil NO^-₃. Residual soil NO^-₃ after harvest increased little with increasing N rates. Grain protein, yield, and quality varied depending mainly on the year and amount of precipitation during grain filling. A topdress N rate of 200 kg N ha^-1 would be the most appropriate way to produce high quality bread-making wheat and minimize the risk of NO^-₃ leaching.

Abbreviations: HFN, Hagberg falling number • SDS, sodium dodecyl sulfate

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
BAKING QUALITY OF WHEAT in commercial cultivars generally depends on the protein concentration of the grain (Gate, 1995; Gooding and Davies, 1997). In turn, protein concentration depends on genotype and is influenced by the environment (mainly climate during the grain-filling period), soil N, and rate and time of supplemental N application (Wuest and Cassman, 1992; Gate, 1995; Gooding and Davies, 1997; López-Bellido et al., 1998). Temperature, rainfall, and solar radiation during grain filling are the climatic factors with the most marked effects on protein concentration in wheat. Growing conditions leading to long grain-filling periods (e.g., northwestern Europe) normally result in well-filled kernels with a low protein concentration (Gooding and Davies, 1997). Temperature and rainfall conditions of Mediterranean regions, such as those in southern Europe, are characterized by dry, hot summers alternating with humid and temperate winters (Nahal, 1991; Acevedo et al., 1999) leading to shorter grain-filling period, lower grain yields, and higher protein concentrations in grain (Borghi, 1997; López-Bellido et al., 1998). This climate offers the opportunity for production of high quality bread wheat, which is lacking in the European Union (Borghi et al., 1997; Corbellini et al., 1998).

Nitrogen fertilization management offers the opportunity for increasing wheat protein content and quality. Reports show that N applications combined with a better distribution of N during the wheat cycle significantly improves bread-making quality (Wuest and Cassman, 1992; Gate, 1995; Borghi et al., 1997; Gooding and Davies, 1997). These reports also show that delayed application of N within the growing season favors protein buildup in the grain over yield and enhances the bread-making quality of the flour. Bread-making quality increases with N supply and reaches a peak at a N level above that needed to achieve maximum yield. Protein quality can decrease with further increases of protein content because the extra N accumulated in grain is represented by gliadins or nonprotein N, which depress bread-making quality (Borghi et al., 1997; Gooding and Davies, 1997). Although high application rates of N fertilizer can increase wheat quality, they may result in NO^-₃ pollution (Chaney, 1990; Addiscott et al., 1992). Nitrogen leaching is a widespread concern not only because of the wasted fertilizer, but also because of regulations limiting NO^-₃ concentrations in drinking water (Rice et al., 1995). It is, therefore, important to devise methodologies directed towards a more efficient use of N fertilizer.

By carefully managing N fertilization, less N may be needed while grain yields and protein may be maintained or increased (Chaney, 1990; Alcoz et al., 1993). Applications of foliar urea [(NH₂)₂CO] can help reduce the NO^-₃ leaching (Gooding and Davies, 1992; Wuest and Cassman, 1992). The use of foliar urea for increasing the protein content of wheat may provide the quality benefits of N fertilization and simultaneously reduce the risks of NO^-₃ leaching or denitrification (Gooding and Davies, 1992; Readman et al., 1997). The application of foliar urea has increased grain protein, particularly late in the season when soil moisture and root uptake are often low (Gooding and Davies, 1992; Barraclough and Haynes, 1996). Yield responses to urea sprays have been highly variable and only increased yield when previous N applications to the soil had been suboptimal. Thus, foliar urea applications are less effective at increasing grain N content when large amounts of N have been applied previously (Gooding and Davies, 1992). Also, yield increases from urea sprays seem more likely in higher rainfall areas because of higher yield potential and greater NO^-₃ leaching (Gooding and Davies, 1992).

In the Mediterranean irrigated areas of the Ebro Valley, wheat is grown in rotation with maize (Zea mays L.) and alfalfa (Medicago sativa L.). Growers try to make wheat cultivation profitable by planting high-priced quality wheat and applying higher N rates with irrigation. These practices may increase costs and environmental pollution (Abad et al., 1996). The climatic conditions of the Mediterranean areas, characterized by increasing water deficit and thermal stress during grain filling, may cause large fluctuations in grain yield, grain protein content, and rheological properties of the dough (Borghi et al., 1997). Extensive research addressed the effect of N on wheat quality, yield, and NO^-₃ leaching in central Europe, Argentina, or USA (Gooding and Davies, 1997; Dilz, 1988; Raun et al., 1999; Satorre and Slafer, 1999). However, there is little information about these factors from irrigated Mediterranean regions where bread-making quality is normally higher (Corbellini et al., 1998; Borghi, 1999) and year-to-year rainfall variability makes it difficult to establish agronomic practices (Acevedo et al., 1999). Thus, it is important to develop rational practices for N fertilization for high quality wheat grown with irrigation in Mediterranean areas.

The objectives of this research were to study and quantify the effects of topdress N fertilization on grain yield and quality while determining the effects of N on the risk of NO^-₃ pollution under irrigated conditions.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field experiments with wheat were conducted in irrigated conditions during two growing seasons (1996–1997 and 1997–1998) at the IRTA (Institut de Recerca i Tecnologia Agroalimentaries)–University of Lleida research fields at Gimenells and Palau de Anglesola (Palau, Ebro Valley, Spain; 41°39' N, 0°51' E) on Calcixerolic Xerochrept soils. The trials were located in a different area of their respective fields in each growing season. The soil plow layer was of loam texture with 22.1 to 24.8% clay, and the soil depth was about 60 cm. In all trials, maize was the previous crop.

Broadleaf weeds were controlled by applying 2.5 L ha^-1 herbicide mixture of 15% Bromoxymil (3,5-dibromo-4-hydroxy-benzonitrile), 15% Ioxynil (4-hydroxy-3,5-diiodobenzonitrile), and 70% MCPA (2-methyl-4-chlorophenoxyacetic acid). Tralkoxydim {2-[(1-ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-tri-methylenyl)cyclohex-2-enone} at a rate of 375 g a.i. ha^-1 was used to control wild oat (Avena sterilis L. subsp. ludoviciana and A. sterilis subsp. sterilis).

The experiments were established on 26 and 28 Nov. 1996 at Palau and Gimenells, respectively, and on 18 and 21 Nov. 1997 at Palau and Gimenells, respectively. Mean temperatures, mean maximum temperatures, rainfall for the 1996–1997 and 1997–1998 wheat growing seasons (November–July), and long-term averages are presented in Table 1. Crops were irrigated three times in the spring. A total of about 130 mm of water was applied between 11 and 17 March, 14 and 24 April, and 9 and 17 May. Wheat received a preseeding broadcast fertilizer application of 43, 83, and 30 kg ha^-1 P, K, and N, respectively.

View this table: [in this window] [in a new window]   Table 1. Mean (Tm) and maximum (Tmax) air temperatures and rainfall during the experiment at two locations.

The initial soil analyses are presented in Table 2. For the determination of soil NO^-₃, samples were collected every year from each plot in autumn before N application and after harvest. Soil was sampled from 0 to 30 cm and from 30 to 60 cm using Eijkelkamp cylindrical augers. Soil NO^-₃ was extracted with KCl, measured with a colorimetric procedure (Keeney and Nelson, 1982), and converted to kg N ha^-1, taking a soil bulk density of 1300 kg m^-3. The average soil NO^-₃ contents at the beginning of each growing season are presented in Table 3.

Grain protein was determined by near-infrared reflectance spectroscopy, using a Technicon Infra Analyzer 400 instrument (Bran and Lubbe, Hamburg, Germany), and presented on a dry matter basis. Test weight was obtained with a standard chondrometer. A sodium dodecyl sulfate (SDS) sedimentation volume test (Peña et al., 1990), a modification of the Axford et al. (1979) test that uses 1 g of flour sample at 14% moisture, was performed as an indicator of protein quality. The Hagberg falling number(HFN) was measured using an apparatus with automatic stirring (Falling Number AB, Stockholm, Sweden) to assess -amylase activity in the grain (Standard Method 107/1, ICC, Schwechat, Austria). Bread-making quality of the wheat was evaluated with the Chopin alveograph according to ICC Standard Method 121 (ICC, 1992). This instrument measures the rheological properties of dough prepared from flour and water under standardized conditions. The dough was formed into disc-shaped pieces that were inflated into bubbles. The pressure variation inside each bubble was recorded as a graph (alveogram) (Borghi et al., 1997; Walker and Hazelton, 1996). The maximum height along the ordinate axis is referred to as P and estimates the resistance of the dough (measured in mm). Its length along the x-axis is referred to as L and is a measure of dough extensibility (L is measured in mm). Finally, the area under the graph is proportional to the energy required to cause the test piece (or dough bubble) to break and is referred to as W (Borghi et al., 1997; Gate, 1995).

The experimental design was a split-plot model with completely randomized blocks and four replications. All treatments were randomized every year. Nitrogen fertilizer treatments were the main plots, and cultivars were subplots. The results were subjected to analysis of variance with the General Linear Model procedure of SAS (SAS Inst., 1989). Statistical differences between several treatments were determined by single degree-of-freedom orthogonal contrasts.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Grain Yield and Plant Parameters
The growing season significantly influenced grain yield. The average yields in 1997 were 6888 kg ha^-1 compared with 4771 kg ha^-1 in 1998, probably because of higher precipitation and lower maximum temperatures during grain filling in 1997. The monthly rainfall for June 1997 was 82 and 102 mm at Gimenells and Palau, respectively. However, in June 1998, the rainfall was only 0.6 and 1.5 mm, and wheat was not irrigated during that month. The average grain yields in these experiments were similar to those reported for other Mediterranean-type areas under irrigation (Wuest and Cassman, 1992) but are considerably lower than the 8000 to 10000 kg ha^-1 reported from central Europe, which had a longer growing season, better rainfall distribution, and mild temperatures during grain filling compared with Ebro Valley (Dilz, 1988; Barraclough and Haynes, 1996).

There were significant cultivar x location interactions (P 0.01) for grain yield. Gazul, a more modern cultivar than Rinconada, performed better than Rinconada at Palau, whereas Rinconada gave higher yields than Gazul at Gimenells. In the irrigated areas of the Ebro Valley, both cultivars are known for high protein and quality but lower yield than low quality cultivars such as Anza (López and Serra, 1996).

Nitrogen fertilization increased yields at Palau de Anglesola (Table 4) in 1997 and 1998, and spikes and kernels per spike in 1997, mainly when increasing N from 100 kg ha^-1 to higher rates. However, at Gimenells, the effects were not statistically significant, possibly due to increased lodging with high N rates, high soil NO^-₃ contents at seeding, or higher maximum temperatures that reduced the duration of grain filling (Tables 1 and 3). The greater effect of N fertilization at Palau that at Gimenells was probably due to the lower initial soil NO^-₃ levels. The NO^-₃ levels at 0- to 30-cm depth were 19.8 and 20.2 mg kg^-1 in 1996 and 1997, respectively, at Palau compared with 36.2 and 53.6 mg kg^-1 at Gimenells. Also, the higher precipitation and lower maximum temperatures during grain filling at Palau (April, May, and June shown in Table 1) may have increased grain yields by allowing greater expression of the N response potential. The average date of heading was 8 April for Rinconada and 12 April for Gazul.

The application of foliar urea did not increase grain yield in any location, suggesting that the N rates used were too high to obtain any yield improvement with late applications of N. These results coincide with reports showing that increases in grain yield following late-season urea applications were found only when previous N applications were insufficient to obtain maximum yield (Gooding and Davies, 1992). The same authors also reported a significant increase in grain-specific weight with the application of foliar urea in certain conditions. However, foliar urea only increased specific weight in one of our experiments, which suggests that the lowest topdressed N rate used was high enough to obtain a high specific weight.

Grain Quality
Hagberg falling number and W were higher in 1998 than in 1997. This response was opposite to that found for grain yield. The higher yields and lower quality observed in 1997 were probably caused by abnormally high precipitation and lower maximum temperatures during the grain-filling period (June) (Table 1). Late-season rainfall can cause an increase -amylase activity that will result in a drop in HFN and grain quality (Gooding and Davies, 1997). Location affected the quality of the wheat in our study. Gimenells produced wheat of higher quality than Palau, whereas the opposite was true for grain yield. The higher grain quality and lower yield at Gimenells might also be due to the lower rainfall and higher maximum temperatures during grain filling (Table 1). Increased temperature during grain filling tends to increase grain protein content and grain quality as measured by dough strength and related measures (Stone and Savin, 1999).

The two cultivars differed in quality measurements. The differences were important for HFN and W alveogram in 1997. In that year, when wheat quality was low because of the high rainfall during grain filling, Gazul gave higher quality values than Rinconada. In 1998, however, there were no differences in HFN or W between cultivars. Gazul also produced grain of greater N concentration than Rinconada in three of the four trials. The protein and W values of these cultivars are in the upper range of the high quality bread-making cultivars of Italy (Borghi et al., 1997) and France (Gate, 1995). They are also higher than the British export requirements (W values between 140–180) (Fenwick, 1993).

Grain protein increased with increasing N fertilization rates for both locations and both years (Table 5). This result agrees with reports showing that the influence of N fertilizer on grain quality is mainly through its effects on grain protein concentration (Gooding and Davies, 1997). In our research, the highest grain protein concentrations were achieved with the highest N rate, and higher increases were at Palau probably because of the lower soil NO^-₃ concentrations and higher grain yields at this location. Averaging the two locations and years, the largest increase in grain protein (1.67%) was obtained when N fertilization rates increased from 100 to 200 kg N ha^-1. The second increase from 200 to 300 kg N ha^-1 increased grain protein by 0.89%.

Splitting and delaying N application by spraying the crop with 50 kg N ha^-1 as foliar urea did not significantly increase the percentage of protein and the W (Table 5). However, nonsignificant routine effects of foliar urea W were observed for every year and location. The increase was more visible in 1997 (13% increase on average) when precipitation during the grain-filling period increased yield and reduced quality. The lack of statistical significance for the effects of applying foliar urea on W may be due to the high variability of this parameter. Previous studies have also found that N sprays at anthesis were better at increasing grain N content when climatic conditions favored low grain protein (Gooding and Davies, 1992; Barraclough and Haynes, 1996).

The results of this research show that high rates of N fertilization can increase wheat quality even in Mediterranean areas that traditionally produce high quality wheats. Results also suggest that late applications of foliar urea might be a potential management option for improving grain quality in irrigated Mediterranean areas but only in rainy years.

Soil Nitrate and Nitrogen Balance
Soil NO^-₃ levels after harvest differed between locations. The average NO^-₃ content was higher at Gimenells than at Palau (170 and 72 kg N ha^-1, respectively) probably because of higher initial soil NO^-₃ at Gimenells (Table 3), the lower N grain removal (Table 6), and lower rainfall that might have reduced N leaching. The residual soil NO^-₃ found at Palau and Gimenells was at the lower and higher range, respectively, of values reported by other authors (Chaney, 1990; Readman et al., 1997) but much higher than values reported by Dilz (1988) for wet growing seasons. The average amounts of residual soil NO^-₃ at 0-to 60-cm depth increased significantly with increasing N fertilization at Gimenells in 1998, rising from 141 to 289 kg N ha^-1. In 1997, soil NO^-₃ also increased from 107 to 160 kg N ha^-1 but without statistical significance. Again, the high rainfall during grain filling in 1997 might have leached some of the residual NO^-₃ and reduced the differences between N treatments this year. Soil NO^-₃ content was not affected by the application of foliar urea, however. Increasing N fertilization usually implies an increase in the amount of residual soil NO^-₃ (Chaney, 1990; Addiscott et al., 1992). At Palau, however, the lower amount of initial residual soil NO^-₃, the higher quantity of N removed by the grain, and higher rainfall might have reduced the possible differences among N rates.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The results show that grain yields and quality of irrigated wheat can be greatly affected by the variability of the Mediterranean climate. However, topdressing N fertilizer up to 300 kg N ha^-1 can increase grain quality of high quality cultivars grown in these areas, which are suited for high protein yield and dough W values. An appreciation of the results for grain yield, grain quality, and residual soil NO^-₃ suggests that best results could be achieved by topdressing N fertilizer at a rate of about 200 kg N ha^-1. This rate increased yields without reaching the maximum quality but resulted in low residual soil NO^-₃. In the present situation of increasing environmental concerns, the requirements for high grain protein must be accompanied with farm practices that make efficient use of the fertilizer N and minimize the risk of NO^-₃ losses to water supplies.

	ACKNOWLEDGMENTS

 
This research was supported by ACTEL (Associació de Cooperatives de les Terres de Lleida). We express our gratitude to Dr. R. Salvador, A. Mallarino, L. Gibson, and P. Hinz of the Iowa State University for their technical and statistical assistance and M. Baga, A. Lopez, J. Del Campo, J. Millera, J. Betbese, and R. Mestres of the UdL-IRTA for their field and laboratory assistance.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (10) Citing Articles via Google Scholar Google Scholar Articles by Lloveras, J. Articles by Solsona, J. Search for Related Content PubMed Articles by Lloveras, J. Articles by Solsona, J. Agricola Articles by Lloveras, J. Articles by Solsona, J. Related Collections Wheat Nutrient Management Soil Fertility and Productivity Other Soil Management Irrigation