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Chilean journal of agricultural research

versión On-line ISSN 0718-5839

Chilean J. Agric. Res. v.70 n.1 Chillán mar. 2010

http://dx.doi.org/10.4067/S0718-58392010000100013 

Chilean Journal of Agricultural Research 70(1):122-131 (January-March 2010)

RESEARCH

Effects of Nitrogen on Productivity, Grain Quality, and Optimal Nitrogen Rates in Winter Wheat cv. Kumpa-INIA in Andisols of Southern Chile

Efecto del Nitrógeno en Productividad, Calidad del Grano y Dosis Óptimas de Nitrógeno en Trigo Invernal cv. Kumpa-INIA en Andisoles del Sur de Chile


Ricardo Campillo1*, Claudio Jobet1, and Pablo Undurraga2

1Instituto de Investigaciones Agropecuarias INIA, Casilla 58-D, Temuco, Chile. *Corresponding author (rcampill@inia.cl).
2Instituto de Investigaciones Agropecuarias INIA, Casilla 426, Chillán, Chile.

Received: 30 January  2009.                           Accepted: 30 June 2009.


ABSTRACT

Nitrogen is one of the main inputs of the winter wheat crop (Triticum aestivum L.) in southern Chile. Nitrogen efficient management is basic to optimizing its utilization while decreasing pollution risks and operational costs. Crop response and N use efficiency (NUE, defined as the ratio of yield to mineral N supply, regardless of source) are important for evaluating N requirements of winter wheat, and reaching maximum and economic yields. The objective of this study was to determine the effect of N rate on grain yield, calculate the N rate that maximizes yield, and estimate the optimal grain yield rate and quality of high-yielding winter wheat cv. Kumpa-INIA. Five annual N rates were evaluated in a randomized complete block design during two successive winter wheat cropping seasons on a Vilcún series soil of the Pachic Melanudands family (Andisol) in La Araucania Region, Chile, and subjected to intensive annual crop rotation. Significant effects (P ≤ 0.01) of N rate on grain yield and quality were found. The optimal physical N rate (OPR) in both seasons ranged from 290 to 339 kg ha-1, whereas optimal economic N rate (OER) ranged from 248 to 274 kg ha-1, with yields between 10.2 and 10.1 t ha-1. Nitrogen use efficiency associated to OER was high in both seasons (36.9 and 41.2 kg grain kg-1 N) and fluctuated in similar ranges. Nitrogen rate increased hectoliter weight and grain protein, but decreased NUE.

Key words: nitrogen level, nitrogen use efficiency, Andisols, Triticum aestivum.


RESUMEN

El N es uno de los principales insumos del cultivo de trigo (Triticum aestivum L.) en Chile. Su manejo eficiente optimiza las dosis, disminuye los riesgos de contaminación y los costos de producción. La respuesta del cultivo y eficiencia de uso de N (NUE, definida como la razón de rendimiento y suministro de N mineral, independientemente de la fuente) son importantes para evaluar los requerimientos de N y alcanzar rendimientos máximos y económicos. El objetivo de este estudio fue determinar el efecto del N en la producción y las dosis que optimizan la productividad y calidad de grano de trigo invernal cv. Kumpa-INIA. Durante 2 años sucesivos en campo, se estudió en un diseño de bloques completos al azar el efecto de cinco dosis de N en un suelo serie Vilcún de la familia de los Pachic Melanudands (Andisol) de la Región de La Araucanía, Chile, bajo rotaciones intensivas de cultivos anuales. El N tuvo un efecto en la productividad y calidad del grano cosechado (P ≤ 0,01). Las dosis óptimas físicas (OPR) de N en ambas temporadas alcanzaron entre 290 y 339 kgha-1, mientras que las dosis óptimas económicas (OER) de N fluctuaron entre 248 y 274 kg ha-1, con rendimientos entre 10,2 y 10,1 t ha-1. Las NUE asociadas a las OER fueron altas en ambas temporadas (36,9 y 41,2 kg grano kg-1 N) y fluctuaron en rangos similares. El incremento de N elevó el peso hectolitro y el contenido de proteína del grano (P ≤ 0,05), mientras que disminuyó la NUE.

Palabras clave: dosis de nitrógeno, eficiencia de uso de nitrógeno, Andisoles, Triticum aestivum.


INTRODUCTION

Wheat productivity and quality in southern Chile is conditioned by diverse factors of which climate, genetics, and crop management are the most relevant. Chilean wheat productivity is the highest in the Southern Cone and is sustained by the use of high-yield potential varieties that require, among other things, an intensive use of inputs such as fertilizers (Fundación Chile, 2005).

High yields are the result of environmental, technological, management, capital, and input conditions. High wheat yields require increases in N application and the excessive addition of this nutrient can contribute to watercourse pollution (Semenov et al., 2007). Therefore, the use of high N rates that allow expressing yield potential of existing varieties in the actual market require careful and efficient management of nutrient partialization with the purpose of minimizing losses due to lixiviation during crop development, avoiding pollution of the underground water tables and its harmful effect on human health and environmental sustainability.

It is actually estimated that global grain demand will be duplicated by the year 2050 (Cassmann, 1999; Tilman et al., 2002). Cereal producers are under pressure to increase their yields and maintain their profitability despite a group of environmental restrictions and high fertilizer costs (Semenov et al., 2007). Compared to other Southern Cone countries, Chile presents high input costs for fertilizers and pesticides, costs which are one of the factors affecting total production cost the most (Fundación Chile, 2005). In general, the international price of fertilizers, as for many other products, has been rising in the recent past. However, the increase experienced by fertilizers is significantly greater than that recorded for other products such as wood, grains, food, and energy (ODEPA, 2008a).

Fertilizers represented 30% of direct crop costs in Chile (Fundación Chile, 2005) in a mean yield situation (5 to 6 t ha-1), increasing to 36% in high-yield management (over 8 t ha-1). However, during 2008, this direct cost has escalated to 47% as a result of the high price increase in input and raw materials, such as oil and natural gas that are so important for the production of ammonium N fertilizers (ODEPA, 2008a). Although fertilizer prices have returned to their original prices during 2009 as a consequence of the severe international economic crisis, it is quite probable that the phenomenon will occur again in the medium-term given its dependence on the price of fossil fuels and its condition of non-renewable resource. Among the fertilizer inputs used in wheat crops, N fertilizer normally affects production costs more than other inputs (Fundación Chile, 2005).

Greater knowledge about the factors that determine the rational use of N allows producers to be more efficient from the technical as well as economic point of view in the use of fertilizers through adequate agronomic and environmental practices (Parodi, 2003). Production of high wheat yields requires the application of high N rates, and the excess of this nutrient can promote watercourse pollution. This constitutes an incentive to maximize N use efficiency (NUE) in productive systems.

Moll et al. (1982) defined NUE as grain production per unit of available N in the soil. These authors indicated that available N in the soil and total N in the plant are difficult to measure adequately. They proposed substituting these measurements for N fertilizer and N from the aerial part of the plant, respectively. In addition, they established that NUE can be divided in the components of N uptake efficiency (N in the plant per unit of N fertilizer), and N utilization efficiency (grain yield per unit of N in the plant). The product of these two components is expressed as NUE (Moll et al., 1982; Ortiz-Monasterio et al., 1997; Dawson et al., 2008).

A similar approximation was stated by Semenov et al. (2007) who defined NUE as the ratio between yield and input of N mineral regardless of source: NUE = Y Ns-1, where Ns (kg ha-1) is available N for the plant during the growth period, including initial inorganic N in the soil, applied N fertilizer, and mineralized N from organic N during the growth period, and Y is grain yield (kg ha-1). The atmospheric contribution of N was not considered because it represents a negligible source in relation to the others (Cassman et al., 1998). In this case, for both N efficiency and absorption from the soil Ncrop Ns-1 and N conversion into grain yield Y Ncrop-1 can be expressed as Y Ns-1 = (Ncrop Ns-1) (Y Ncrop-1).

There are also alternative definitions of NUE in the literature (Cassman et al., 1998; Tilman et al., 2002; Raun et al., 2002) and it is known that there are substantial discrepancies on how NUE should be defined. The objective of this study is not to thoroughly analyze this topic. Given that we are interested in considering the productive value of N, the definition of NUE adopted in this article is the ratio of yield related to N mineral input regardless of source (Moll et al. 1982; Semenov et al., 2007).

Obtaining high NUE is very important in actual crop production. Nitrogen use efficiency can be increased through the selection of crop growth environment (soil type and climate), management practices (sowing date, rate, and partialization of N application), and crop breeding (Semenov et al., 2007).

Nitrogen use efficiency in cereals (calculated as NUE = (total cereal N removed - (N soil + N rain))/N cereal fertilizer) is actually estimated at 33% (Raun and Johnson, 1999), a figure quite lower than the 50% normally reported in the literature (Rodríguez, 1991). Various 15N recovery experiments have reported losses of 20 to 50% of N fertilizer in wheat, attributed to the combined effects of denitrification, volatilization, and lixiviation (Raun and Johnson, 1999; Urquiaga, 2000). Field experiments in Central Europe have recorded, on the average, 50 to 60% recovery of N fertilizer applied to winter wheat (grain and chaff) (Blankenau et al., 2002; Macdonald et al., 2002).

Modifying the timing and the application method of N can also lead to an improvement in absorption efficiency. One of the main causes of low NUE in actual N management practices is the scarce synchrony between N soil input and crop demand (Raun and Johnson, 1999; Cassmann et al., 2002; Fageria and Baligar, 2005).

Producers are sowing a wide range of new wheat cultivars in southern Chile which require high annual rates of N to describe their productivity. La Araucanía Region presents a large area of annual crops in which wheat dominates. During the 2006-2007 season, this region had a planted area of 230 070 ha of annual crops of which 107 800 ha were wheat with a mean yield of 4.60 t ha-1 (ODEPA, 2008b).

Winter wheat 'Kumpa-INIA' is characterized by its high yield potential in the southern zone of Chile, normally reaching the maximum grain yields among the different winter cultivars on the market with productivity over 11 t ha-1 in areas of more than 200 ha sown. Its agronomic type, reed firmness, high number of ears, and leaf color has allowed it to become a variety that is suitable for the demanding conditions of southern Chile. 'Kumpa-INIA' was officially released in 2002 for the National Wheat Program of the Instituto de Investigaciones Agropecuarias (INIA), Temuco, and available to regional agriculture in the 2003 season. Results have given it a high yield potential for an important area which covers localities from the Bío Bío Region to Los Lagos Region with acceptable quality and sanitation. Height of the adult plant varies between 85 and 100 cm with a mean of 95 cm, a stem resistant to lodging which allows it to adapt to the conditions in southern Chile (Jobet and Hewstone, 2003). The vegetative period from sowing to ear formation in Temuco (La Araucanía Region) is about 182 to 184 d, approximately 189 d in Purranque (Los Lagos Region), and is actually one of the most recommended late varieties. Its quality, measured by its humid gluten, sedimentation, protein content, and alveogram (Jobet and Hewstone, 2003) locates it in the intermediate wheat category in accordance with the Chilean Norm (Instituto Nacional de Normalización, 2000).

The objective of this study was to determine the effect of N on wheat grain production, hectoliter weight, and grain quality, as well as estimating rates that optimize productivity in a high-yield wheat cultivar such as Kumpa-INIA in an Andisol in the La Araucanía Region subjected to more than 20 yr of intensive annual crop rotation.

MATERIALS AND METHODS

The study was carried out on the property of a cereal producer in the commune of Vilcún (38º41' S, 72º25' W, 200 m.a.s.l.), La Araucanía Region, Chile, during two consecutive seasons (2004-2005 and 2005-2006). The soil corresponded to a Vilcún series, member of the medial, isomesic of the Pachic Melanudand (Andisol) family (CIREN, 2002). This soil was subjected to an intensive annual crop rotation under the no-till system with burning of harvesting residues. The initial characterization of the soils was carried out in accordance with methodologies established in Sadzawka et al. (2006) (Table 1). The chemical analyses of both sites were carried out in the INIA Soil Analysis Laboratory. Both sites corresponded to different fields of the same property, presented adequate fertility levels with moderate acidity limitations, and a low initial N level.

Table 1. Chemical characterization of soil (0-20 cm) before establishing experiments. 2004-2005 and 2005-2006 seasons.

 

The randomized complete block experimental design was used with four replicates in 10 m2 (2 x 5 m) plots. Five treatments were evaluated consistent with annual rates of N: 0, 150, 200, 250, and 300 kg ha-1 with the commercial N fertilizer (CNF) urea (46% N). In the treatments that considered annual rates of N, initial fertilization with calcium ammonium nitrate (40 kg ha-1 N) was deducted.

The soil received lime neutralization 1 mo before sowing equivalent to 3 t ha-1 (May 2004) and 1 t ha-1 (May 2005) of pure CaCO3 (Soprocal calcium correction, equivalent to 90% calcium carbonate) to prevent damage from the acidifying effect of CNF (Campillo and Sadzawka, 2006). Total CNF rate was partialized in four applications, the corresponding decimal code is indicated between parentheses for the cereal growth stages according to Zadoks et al. (1974): at sowing (Z0); two tillers (Z22); end of tillering (Z30), and two nodes (Z32). In the sowing furrow, 40 kg ha-1 N was applied as calcium ammonium nitrate (27-0-0-5% MgO-7% CaO). The rest of each evaluated N rate was applied as CNF and partialized in the Z22, Z30, and Z32 stages in the following way: N150 (50+60+0); N200 (80+40+40); N250 (80+90+40), and N300 (80+140+40).

In both years, sowing was done with an assay rototiller (Planet Junior, Allen Co, New Jersey, USA). Soil samples were collected for chemical characterization before sowing and just after harvest. Sowing dates were 17 June 2004 and 22 June 2005. Wheat sown was cv. Kumpa-INIA (winter wheat) with oat (Avena sativa L.) as the previous crop. Seed rate was 200 kg ha-1, disinfected with 200 g L-1 doses of triticonazole (Real 200 SC, BASF).

A fertilization base was established for the crop to compensate any nutritional limitation that is not N. A fertilization base was applied (per ha) in the sowing furrow consisting of 150 kg P2O5 (triple superphosphate), 55 kg K2O, 55 kg S, 45 kg MgO (sulpomag), 2.5 kg B (boronatrocalcite), and 2.2 kgZn (zinc sulfate). This sowing fertilization was complemented with a random cover application of 50 kgK2O and 18 kg S (potassium sulfate).

The chemical control of weeds in both seasons was carried out in postharvest with prosulfocarb (AFIPA, 2006) in 4 L ha-1 rates (Falcon, SYNGENTA) for the control of preemergent gramineae. The full tiller stage (Z26) was complemented with iodosulfuron-methyl-sodium in 50 g kg-1 rates (Hussar 20 WG, BAYER) to control gramineae and broad leaf.

In the phenological stage Z30 of the 2004-2005 season, prochloraz + carbendazim fungicides were used in rates of 300 g L-1 + 80 g L-1 (Sportak 40 EC, ANASAC CHILE) and benomyl in rates of 500 g kg-1 (Benlate, ARYSTA LIFESCIENCE). This same application was repeated for the Z32 and Z39 stages to prevent the presence of leaf diseases. Foliar diseases in the 2005-2006 season were controlled in a similar way with prochloraz and benomyl fungicides. The phytoregulator chlormequat chloride + choline chloride was used in both seasons in the Z28 stage with 460 g L-1 + 320 g L-1 rates (Cycocel extra, BASF).

During the summer crop growth period, soil samples were collected (depths of 0-20 and 20-40 cm) to determine the evolution of the gravimetric humidity content (dry weight base) in the root zone (Campillo et al., 2007). Experiments were harvested on 15 February 2005 and 20 February 2006. Grain yield was determined with 14% dry weight humidity base (DWHB), hectoliter weight, and grain N by the combustion method with a macro elemental analyzer (Vario MAX CNS, Elementar, Germany, 2001; Bremmer and Mulvaney, 1982). Protein content was obtained with a conversion factor (%N x 5.7). Grain yield data, hectoliter weight, and grain protein were subjected to ANOVA and treatment means to Tukey test (P ≤ 0.05) when applicable (SAS Institute, 1990).

It was possible to establish the optimal physical rates (OPR) of N derived from the experiment and its corresponding maximum grain production yield by adjusting a second degree polynomial to the grain yield results of 'Kumpa-INIA' wheat (Volke, 1982; Rebolledo, 1999; Campillo et al., 2007). Fertilizer N cost (FNC) and a value per ton of wheat was assumed in order to calculate the relationship of input prices/product and estimate the optimal economic rates (OER) of N and its respective grain production optimal economic yield. The unlimited capital economic criterion was used with the restriction of a 50% minimum rate of return (Volke, 1982).

RESULTS AND DISCUSSION

In general, the year 2004 showed abundant precipitation (1559 mm) through spring, thus ensuring a good water supply (525 mm from September to February) for wheat crop development. There were no important humidity restrictions in both soil strata (0-20 and 20-40 cm), maintaining content over 50% usable humidity during most of crop development (data not shown). Climatic information during the 2005-2006 season (1892 mm) showed a similar situation with abundant precipitation during most of the year (568 mm for September to February) ensuring an adequate water supply for all crops in the zone. As a result, during 2005 soil water content was maintained close to field capacity during most of the crop development period. This background information allows stating that the wheat crop was not affected by hydric stress, thus ensuring normal grain filling.

Grain production of cv. Kumpa-INIA in both seasons increased (P < 0.01) with N rates, showing a low coefficient of variation (4.7 to 5.1%). Grain yield for the two seasons (Tables 2 and 3) was between 3.85 (control without N) and 10.42 t ha-1 (300 kgha-1 N). The most efficient production in both cases was associated with the highest annual N applications.

Table 2. Effect of N rate on grain yield and N use efficiency (NUE) of wheat cv. Kumpa-INIA, 2004-2005 season.

Table 3. Effect of N rate on grain yield and N use efficiency (NUE) of wheat cv. Kumpa-INIA, 2005-2006 season.

This study defined NUE as grain production per unit of N supplied (i.e. available N for the plant during the growth period, including initial inorganic N in the soil, applied N fertilizer, and mineralized N from organic N during this period) (Moll et al., 1982; Ortiz-Monasterio et al., 1997; Semenov et al., 2007). This NUE decreased in both seasons (Tables 2 and 3) as a function of the increase of the annual applied rate.

Nitrogen use efficiencies calculated for cv. Kumpa-INIA were high and relatively stable in both seasons, fluctuating between 58.9 and 34.5 (2004-2005) and between 56.8 and 34.2 (2005-2006). The 250 kg ha-1 N rate had a high productive and economic efficiency since it was associated with the optimal economic rates estimated from the quadratic model (Tables 2 and 3).

Nitrogen use efficiencies calculated for cv. Kumpa-INIA were higher than the values normally pointed out in other research studies. López-Bellido et al. (2006) found that wheat NUE fluctuated between 19.2 and 20.6 with 150 kg ha-1 during a 3-yr period when comparing different partializations of N in a Vertisol characteristic of the Mediterranean region in Andalucía, Spain. Díaz et al. (2002) found that NUE was lower than 6 kg grain kg-1 N applied with a rate of 240 kg ha-1 in annual sowing of winter wheat in Andisols of the foothills of the Bío Bío Region, Chile. However, Mellado (1992), who partialized the N rate in an Andisol in the Province of Ñuble, Chile, determined that a 150 kg ha-1 N application achieved the highest NUE in the tiller stage of winter wheat, varying between 22 and 30 over a 4-yr period. Ortiz-Monasterio et al. (1997) compared NUE of 10 wheat cultivars produced by CIMMYT (Centro Internacional de Mejoramiento del Maíz y Trigo) in Sonora, Mexico, and found that the mean NUE was 35 kg grain kg-1 N with a rate of 150 kg ha-1 N and 18 kg grain kg-1 N with 300 kgha-1 N.

It has been established that the application of N fertilizer can increase both the yield and the protein content of the grain (Fowler et al., 1990). Nitrogen use efficiency is greater when the yield response to N is high. Therefore, this efficiency is generally high with low N rates and decreases in accordance with the rate increase of applied N (Campbell et al., 1977; Clarke et al., 1990; Gauer et al., 1992; Parodi, 2003).

For the optimization process and calculation of N rates, both physical and economic, a second degree polynomial was adjusted to the grain yield results of cv. Kumpa-INIA obtained in both productive cycles. In this way, it was possible to estimate the optimal physical rate (OPR) of wheat production and its corresponding maximum yield (Figures 1 and 2).

Figure 1. Increase of wheat yield according to annual N rate. 2004-2005 season.

Figure 2. Increase of wheat yield according to annual N rate, 2005-2006 season.




The relationship of input prices/product was calculated from the fertilizer N cost (FNC) and the value per ton of wheat, and it was possible to determine the optimal economic rate (OER) of N for wheat production and its respective optimal economic yield. The unlimited capital economic criterion was used with the restriction of a 50% minimum rate of return (Volke, 1982; Rebolledo, 1999).

During the 2004-2005 season (Table 4), OPR reached 290 kg ha-1, OER 248 kg ha-1, and an optimal yield of 10.22 t ha-1. In the second season (2005-2006), optimal yield for 'Kumpa-INIA' was similar to the above-mentioned (10.13 t ha-1), but both estimated OPR (339 kg ha-1) and OER (274 kg ha-1) required for optimal yield showed an increase. That is, to obtain a similar grain yield, a smaller quantity o N applied to the crop was required during the 2004-2205 season in relation to the requirements of the following season. This production and optimized rates concur with NUE calculated for cv. Kumpa-INIA during the first year (Table 2), which were more efficient in productive and economic terms than those obtained in the second season (Table 3). Similar OER values of N and NUE of this Andisol Vilcún have been reported with sowings of alternative-habit wheat (Campillo et al., 2007).

Table 4. Optimization of N rates in wheat cv. Kumpa-INIA, 2004-2005 and 2005-2006 seasons.

It is important to remember that CNF applied in the Andisols was quickly enzymatically hydrolyzed in 1 or 2 d (Campillo and Rodríguez, 1984). Subsequently, its behavior in the soil is similar to any other form of ammonium N (Campillo and Rodríguez, 1984; Rodríguez, 1991), so that in 2 or 3 wk both calcium ammonium nitrate (applied to the sowing furrow) and CNF experience similar transformations in the nitrification process.

Soil analysis carried out at harvest of the wheat crop of the 2004-2005 season (Table 5), showed that soil acidity (water pH, exchangeable Ca, exchangeable Al, and Al saturation) were maintained without any significant changes because of the effect of the annual N rates applied as CNF.

Table 5. Effect of N rate on acidity parameters of Andisol Vilcún series at harvest of wheat cv. Kumpa-INIA. March 2005.


This means that despite the known acidifying effect of CNF used, no adverse changes were apparent in the soil acidity parameters due to the corrective effect of lime neutralization that was applied in cereal pre-sowing. Similar results have been reported for this Andisol in alternative-habit wheat sowings with a high yield potential (Campillo et al., 2007). Lime neutralization is recommended when acidifying reaction fertilizers are applied in soils that did not initially show limitations due to acidification. This practice makes the use of acidic reaction fertilizers possible, such as CNF, neutralizing them with moderate applications of calcium carbonate (pre-sowing) to prevent eventual damage in crop development and production (Rodríguez, 1991; Suárez, 1994; Campillo and Sadzawka, 2006).

The increase in the level of applied N also increased hectoliter weight of the wheat grain (Table 6). In the first season, the 250 kg ha-1 N rate obtained 82.5 while the 300 kg ha-1 N rate reached 83.1 with no differences between them (P > 0.05). During the second season, the 250 kg ha-1 annual N rate obtained 81.7 and was greater than (P < 0.05) the rest of the N rates. These results indicate that the best hectoliter weight was obtained with 250 kgha-1 annual N. In both seasons, and in the whole range of N fertilizer rates assayed, grain hectoliter weight values were always higher than the normal values considered for cv. Kumpa-INIA (Jobet and Hewstone, 2003), thus ratifying the good climatic conditions apparent during grain filling.

Table 6. Effect of N rate on hectoliter weight of wheat grain cv. Kumpa-INIA, 2004-2005 and 2005-2006 seasons.


Wheat grain protein percentage is frequently used as the main measurement of grain quality. Nitrogen fertilizer is one the most used tools to influence grain yield and quality, a fact based en general knowledge that this nutrient can increase grain yield, grain protein percentage, or both (Stone and Savin, 1999). Maximum protein values were restricted to high N rates in both seasons. Protein value in the first season reached 11.29% (300 kg ha-1 N rate) and was higher (P < 0.05) than 10.32% (250 kgha-1 N rate). In the 2005-2006 season, protein values were 11.30% (300 kg ha-1 N rate) and 11.89% (250 kgha-1 N rate) with no difference (P > 0.05) between N rates (Table 7). As for hectoliter weight, grain protein values obtained in this experiment were high and similar to levels reported as normal for cv. Kumpa-INIA (Jobet and Hewstone, 2003). These results coincide with evaluations of various spring wheat cultivars carried out in Manitoba, Canada, where the increase in the level of N increased protein and N absorption while decreasing NUE (Gauer et al., 1992). At the same time, a study carried out in Eastern Canada to establish OER of N with a spring wheat cultivar using the 15N methodology, Tran and Tremblay (2000) found that protein concentration in the wheat grain increased linearly with N rate.

Table 7. Effect of N rate on protein content of wheat grain cv. Kumpa-INIA, 2004-2005 and 2005-2006 seasons.



CONCLUSIONS

Optimization of N fertilization of wheat cv. Kumpa-INIA in Andisols of the La Araucanía Region, Chile pointed out an OPR of 290 kg ha-1, OER of 248 kg ha-1, and optimal economic yield of 10.22 t ha-1 in the 2004-2005 season. Optimal economic yield was similar (10.13 t ha-1) in the second season (2005-2006), but both OPR (339 kg ha-1) and OER (274 kg ha-1) showed increases.

The increase of applied N continuously decreased NUEs (kg of grain produced kg-1 N supplied) in both productive cycles. Nitrogen used efficiencies calculated for cv. Kumpa-INIA were high with a range variation from 58.9 to 34.5 (2004-2005), and 56.8 to 34.2 (2005-2006). Nitrogen used efficiencies associated with OERs of N were 41.2 and 36.9 in both seasons. These values suggest that N fertilizer management during the crop development cycle was adequate and efficient.

Wheat grain hectoliter weight during both seasons increased with the level of N applied. The highest hectoliter weight values (82.5 and 83.1) in the 2004-2005 season of cv. Kumpa-INIA were associated to annual N rates of 250 and 300 kg ha-1 with no differences (P > 0.05) between them. The annual N rate of 250 kg ha-1 in the second season was 81.7 and was higher (P < 0.05) than the other N rates. Hectoliter weight values in both productive cycles were high and greater than the values considered as normal for cv. Kumpa-INIA.

The increase in the level of applied N increased grain protein percentage in both seasons. Protein value in the first season reached 11.29% (300 kg ha-1 N rate) and was higher (P < 0.05) than 10.32% (250 kg ha-1 N rate). Protein values in the 2005-2006 season were 11.30% (300 kg ha-1 N rate) and 11.89% (250 kg ha-1 N rate) with no difference (P > 0.05) between rates. Grain protein values obtained in this experiment were high and similar to levels indicated as adequate for cv. Kumpa-INIA.

Soil acidity parameters (water pH, Ca and Al exchange, and Al saturation) measured in the 2004-2005 season wheat crop harvest were maintained with no significant changes attributable to annual N rates applied as CNF as a consequence of the corrective effect of lime neutralization applied in cereal pre-sowing.

In accordance with these results, in Andisols of the La Araucanía Region subjected to intensive annual crop rotations, the application of OER around 250 kg ha-1 annual N in high-yield potential cultivars such as Kumpa-INIA supports yields over 10 t ha-1 grain, thus combining high productive, economic, and sustainable efficiency.

ACKNOWLEDGEMENTS

The authors thank Carlos Toro, high-level agricultural technician from INIA-Carillanca for his valuable collaboration in the establishment and management of the field experiments.

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