EFFECT OF NITROGEN FERTILIZATION ON QUALITY AND QUANTITY IN SPRING WHEAT

Aleksander Szmigiel¹, Andrzej Oleksy², Marek Kołodziejczyk^1
1 Department of Plant Production, Agricultural University of Cracow, Poland
² Institute of Plant Production, University of Agriculture in Krakow, Poland

ABSTRACT

The experiment was conducted in 2008–2010 on the experimental field in Prusy near Krakow, a part of the Experimental Station of the Institute of Crop Production of the University of Agriculture in Krakow. The aim of the research was to compare the effect of diversified levels of nitrogen fertilization on grain yield, its structure and protein content in grain in two spring wheat cultivars. Diversified weather conditions during the period of investigations and the cultivar factor influenced the level of spring wheat yielding ability. Nitrogen fertilization caused a significant increase in grain yield to the dose of 90 kg N, at which the greatest grain yield was observed. Bigger doses of 120 and 150 kg of nitrogen did not cause any significant increase in the level of yield, on the contrary, a declining tendency in yielding was observed. Among the grain yield components only the number of ears per area unit remained under the influence of the weather conditions. The number of grains per ear and 1000 grain weight, remained similar as the number of ears depended on the cultivar. On the other hand, the level of nitrogen fertilization affected the increase in ear density and 1000 grain weight until the dose of 60 kg N∙ha^-1. It was concluded that protein content in grain depends on the prevailing weather conditions, cultivar and nitrogen fertilization levels. Among the compared cultivars, Bombona c.v. revealed a bigger protein accumulation in grain, which yielded lower than Tybalt c.v. Applied nitrogen doses caused increased protein content in grain within the range from 13.06 to 15.18% when the highest dose of 150 kg N∙ha^-1of nitrogen was applied.

Key words: yield, protein content, yield components, nitrogen, dose.

INTRODUCTION

Numerous research results demonstrate nitrogen fertilization as a factor to the highest degree affecting the quantity and quality of crop grain yields. Efficient utilization of nitrogen by quality wheat, including the spring cultivars depends on the genetic properties of the varieties and cooperation of the site and agro-technical factors [29]. A school of thought considered that higher dose than 160 kg N∙ha^-1 as the proper level of spring wheat fertilization, whereas the doses from 50 to 120 kg N∙ha^-1 as the optimal level [3, 4, 5]. Higher and divided nitrogen doses adjusted to the rhythm of plant growth and development and their needs affects not only the level of yielding but also grain quality [6, 8, 16, 21, 27, 28].

Determining the optimal level of nitrogen fertilization for the new spring wheat varieties were constantly introduced in to cultivation to maintain the amount of grain yields as well as their quality. Increased nitrogen doses may lead to a decline in yielding, however they lead to increased protein content, which is an important element of an assessment of technological and feed usefulness [1, 2].

The research aimed to compare the effect of diversified levels of nitrogen fertilization on the amount of grain yield, its structure and protein content in grain of two spring wheat cultivars to ensure wheat quantity and quality for food security.

MATERIALS AND METHODS

Field experiments were conducted during the years 2008–2010 at the experimental station in Prusy near Krakow (50°07′ N, 20°05′ E) on degraded chernozem, formed from loess, classified in I soil quality class of very good wheat complex. The soil arable layer was characterized by a slightly acid reaction (pHKCl – 6.4), it was highly abundant in phosphorus and magnesium and medium abundant in potassium, respectively: P – 78, K – 141, Mg – 102 mg∙kg^-1. The experiment was conducted by using split-plot method with a control object, in four replications. The area of harvested plot was 16.5 m². The experimental factors comprised of: A = spring wheat cultivars: A1 – Bombona, A2 – Tybalt, B = nitrogen fertilization levels; B1 – 0 (control), B2 – 60, B3 – 90, B4 – 120, B5 – 150 kg N∙ha^-1. Nitrogen was applied in the following combinations:

• B1 = the control without nitrogen fertilization
• B2 = 60 kg N∙ha^-1 (60 pre-sowing)
• B3 = 90 kg N∙ha^-1 (60 pre-sowing+30 shooting)
• B4 = 120 kg N∙ha^-1 (60 pre-sowing +30 shooting +30 pre-earing)
• B5 = 150 kg N∙ha^-1 (90 pre-sowing + 30 shooting + 30 pre-earing).

During the vegetative growth period of wheat nitrogen was applied in the form of 34% ammonium sulphate depending on the dose, either in two doses (prior to sowing, at the shooting phase – BBCH 30) or in three doses (before sowing, at the shooting phase – BBCH 30 and before the heading phase – BBCH 47–49).

Oat was the forecrop for wheat, after its harvesting standard post-harvest and pre-winter measures were applied, and spring measures were conducted before wheat sowing equally. Prior to spring planting, phosphorus and potassium fertilizers were applied in doses 60 kg P2O5 ha^-1 and 80 kg K2O ha^-1. Analyzed spring wheat cultivars were sown in equal plant density of 450 germinating grains per 1m2 at the time optimal for sowing, which in the subsequent years was respectively: 03.04, 08.04 and 01.04. Before sowing the grains were dressed by Oxafun T 75 DS/WS dosed 200 g 100 kg-1of grains. During the period of vegetation weeds were controlled by means of Lintur 70 WG – 150 dm³∙ha^-1 and diseases using Falcon 460 EC – 0.8 dm³∙ha-1, Artea 330 EC – 0.5 dm³∙ha-1, whereas pest were controlled using Karate Zeon 100 CS 1.0 dm³ ha^-1. Grain yield per hectare was determined on the basis of harvest from a plot after conversion to 15% of moisture. On the basis of biometric measurements of 10 plants collected in two replications per plot, the following yielding elements were established: number of ears per 1m2, number of grains per ear and 1000 grain weight. Protein content in grain was assessed in the wheat grain samples by means of Kjeldahl’s method (%N x 5.7: PN-72A-04018). Results of measurements and assessments were elaborated statistically by means of ANOVA using ANALWAR-5FR programme.

The weather conditions during the period of investigations were significantly diversified (Tab. 1). Mean air temperatures during the spring wheat vegetation period in the years of the experiment were similar, however about 1°C higher in comparison with multiannual period. On the other hand, rainfall total was more diversified. In 2008 rainfall was by 118.3 mm lower than average and by 69.4 mm lower than the rainfall requirements of spring wheat, and rainfall deficiency was registered in May and June. Slightly lower than average (14.2 mm) rainfall, but covering the needs of wheat occurred in 2009, while in 2010 the rainfall total from the months of April to June was much higher, exceeding the normal and wheat rainfall needs by 233.4 and 282.3 mm. That year the highest rainfall total, exceeding the normal by 237 mm, was registered in May. Mean air temperature values in respective months were on a higher level than in the multiannual period, except for May 2009 and 2010 and June 2009, when respectively 0.1, 0.6 and 0.3°C temperatures were registered, as well as rainfall higher than the standard and the needs. On the other hand, April 2009 was very warm and dry (rainless) with the temperature higher than the average by 3.3°C and lack of rainfall. Also June 2008 recorded as warm months, since an average air temperature was higher than the standard by 2.0°C at simultaneous rainfall deficiency and June 2010 with the temperature higher than average by 1.1°C and rainfall exceeding the normal by 38 mm. July 2009 and 2010 was very warm, with temperatures higher than average, respectively by 2.0 and 2.8°C.

RESULTS AND DISCUSSION

Analysis of variance revealed a significant effect of the years of research, cultivars and nitrogen fertilization on grain yield of the analysed spring wheat cultivars (Tab. 2). Strongly diversified, considering the rainfall, meteorological conditions during the experiment determined a slight, but significant diversification of spring wheat yielding. The greatest grain yield of wheat cultivars, on average 4.31 t∙ha^-1 was obtained in 2009, characterized by the rainfall total for the period of vegetation approximate to the multiannual period and the highest mean air temperature during the analysed period of research. Slightly lower grain yield was recorded in 2008, when the rainfall total remained lower than the average and rainfall deficiency occurred in May and June, during the period of spring wheat intensive growth, whereas the average air temperature was the lowest over the last three-year period. On the other hand, the lowest and significantly smaller in comparison with 2009, but slightly lower than in 2008 grain yield was obtained in 2010 which was very wet and abundant in rainfall.

Under climatic and soil conditions of Poland crop productivity greatly depends on the rainfall amount. Long term research demonstrated that the quantity of spring wheat grain yield depends on rainfall amount in May and June and on their total over the whole vegetation period [7, 17, 18, 23]. Rainfall amount optimal for wheat cultivated under conditions of heavy soil in the period from April to July ranges from 151 to 200 mm, however increase in the rainfall amount to 300 mm results in a lesser decline in grain yield than the total below 150 mm [20]. Over the three year cycle of research, the highest grain yields, on average 4.31 t∙ha^-1 were obtained in 2009, when the amount of rainfall from April to July was 335 mm. The lowest grain yields, on average 4.10 t∙ha^-1 were obtained in 2010 characterized by rainfall amount 582 mm, whereas 276 mm was noted in May and June, which constituted 190% of multiannual mean rainfall total.

Like in other studies, the cultivars proved to be the factor undoubtedly diversifying grain yield [2, 14, 15, 19, 26]. Irrespective of the year of the experiment, Tybalt c.v. yielded higher than Bombona. Better yielding of this variety was connected with greater number of grains per ear and higher 1000 grain weight (Tab. 3).

In the first year of the experiment (2008) characterized by the lowest precipitation total and rain deficits in May and June, as well as the lowest average air temperature, compared spring wheat cultivars yielded on an approximate level. On the other hand, in the subsequent, wetter years, Tybalt variety yielded better than Bombona, which responded to the rainfall excess in 2010 by a considerable decline in grain yield in comparison with the years 2008 and 2009 (Tab. 2).

Applied nitrogen fertilization caused a marked increase in grain yield to the dose of 90 kg N, at which the largest grain yield was produced. Bigger doses of 120 and 150 kg nitrogen did not cause any marked increase in yielding level, on the contrary, a declining tendency was observed in the level of spring wheat yielding. Borkowska et al. [2] and Mazurek and Kuś [15] observed a similar response to higher nitrogen doses and reported a significant decrease in grain yield in effect of 150 kg N∙ha^-1 dose application. In case of presented experiment such dependence did not occur, but a slight increasing tendency may be observed following the application of 120 and 150 kg N∙ha^-1 in comparison with the 60 kg N∙ha^-1 dose (increase in yield, respectively by 0.23 and 0.21 t∙ha^-1). Very good soil conditions (natural soil fertility) may be a factor limiting effectiveness of high nitrogen doses. The regularity was confirmed by the results of studies conducted by Wróbel [30], who demonstrated a slight, 15% increment of spring wheat yield following the increase in fertilization level from 60 to 120 kg N∙ha^-1. Lesser yield forming effectiveness of increasing nitrogen dose in spring wheat cultivation was proved also by Lόpez-Bellido et al. [12], Lόpez-Bellido and Lόpez-Bellido [13], Lloveras et al. [11] and Kołodziejczyk at al. [9].

In present experiment the wheat response to the level and method of nitrogen fertilization depended on the weather conditions. In dry 2008 grain yield was increasing with growing level of nitrogen fertilization and significant differences were recorded between the doses of 60 and 90 kg N∙ha^-1. A different response was observed in the subsequent wetter years. In 2009, characterised by a very dry spring, significant increase in grain yield was noted only between the control and the smallest dose of 60 kg N∙ha^-1 supplied prior to sowing. The subsequent bigger N doses did not cause any marked increase in wheat yielding level, on the contrary revealed a tendency to decrease wheat yielding. A similar but more intensified phenomenon occurred in 2010 when a notable decline in grain yield was observed under the influence of 150 kg N∙ha^-1 dose in comparison with a lower dose, and the highest grain yield was registered under the influence of 90 kg N∙ha^-1 dose (Fig. 1).

Analysed wheat cultivars grown without fertilization (control object) yielded on a similar level, whereas fertilized by individual nitrogen doses varied significantly by the level of yielding. Tybalt produced higher yields than Bombona which evidences a better nitrogen utilisation by Tybalt variety. Moreover, in case of Bombona c.v. a significant increase in grain yield was registered only in effect of the lowest, 60 kg N∙ha^-1 nitrogen dose, whereas bigger doses did not cause any marked differences in the amount of grain yield. On the other hand, in the case of Tybalt c.v. beside a significant increase in the level of yielding in effect of applied 60 kg N∙ha^-1 dose, a marked diversification was noted between the doses of 60 and 120 and 150 kg N∙ha^-1 (Tab. 2).

Results of numerous investigations demonstrate that intensity of spring wheat cultivation technology, particularly nitrogen fertilization level, most strongly affects the number of ears per area unit, while to a limited degree the number of grains per ear and 1000 grain weight [10, 11, 30]. ANOVA conducted for spring wheat grain yield components did not reveal any significant effect of the weather conditions course in years on the number of grains per ear and a thousand grain weight. However, the weather course modified markedly the number of ears per area unit (Fig. 2a). The greatest canopy density characterized wheat in 2010 and slightly smaller in 2008. However, significantly smaller canopy closure was observed in 2009, most probably due to drought in April, i.e. during the period of wheat emergence and tillering. In presented experiment Bombona c.v. produced a markedly greater number of ears per area unit (Tab. 3). Nitrogen fertilization level significantly increased this element of yield only to the dose of 60 kg N∙ha^-1, while lower doses only slightly influenced wheat canopy closure (Tab. 3). Also a different response of studied cultivars to the weather conditions was observed as regards this feature. In the years 2008 and 2010 spring wheat cultivars developed a similar number of ears per area unit, whereas in 2009 Tybalt c.v. was characterized by the lowest canopy closure, significantly lower than Bombona c.v and markedly lower in comparison to ear density per area unit for the analyzed cultivars in the years 2008 and 2009 (Fig. 2b). Spring wheat cultivars studied in the presented experiment responded to diversified nitrogen fertilization in a similar way.

The number of grains per ear significantly depended on the cultivar. Tybalt c.v. formed a bigger number of grains than Bombona c.v., whereas the nitrogen dose did not affect formation of this feature (Tab. 3). On the other hand, a cooperative effect of vegetation season and cultivar on formation of this element of yielding was determined. In the years 2008 and 2010, analyzed wheat cultivars did not differ with this feature, whereas in 2010 Tybalt c.v. developed more grains per ear, but in the same year revealed the lowest ear density per area unit (Fig. 3).

Conducted analysis of variance revealed a significant influence of the cultivar factor and fertilization level on 1000 wheat grains weight. Tybalt cultivar formed more ripe grains. In result of nitrogen fertilization, 1000 grain weight was increasing up to the dose of 60 kg N∙ha^-1and then under the influence of bigger doses 90, 120 and 150 kg N∙ha^-1revealed a declining tendency. Significant differences in this feature value were registered only between the control and doses of 60 and 90 kg N∙ha^-1 (Tab. 3). Mazurek et al [14] and Mazurek and Sułek [16] maintain that nitrogen fertilization does not affect a thousand grain weight. On the other hand, Rutkowska [24] states that the increase in bigger nitrogen doses cause that spring wheat grain is thinner and therefore a thousand grain weight is lower.

Protein content in spring wheat grain depended on the course of the weather conditions, cultivar and the level of nitrogen fertilization (Tab. 4). The highest protein content (14.78%) was determined in wheat grain from 2009, which was characterized by the highest mean air temperature and precipitations approximate to average, and slightly higher than spring wheat precipitations needs. Significantly lower, although on the level of 14% protein content was assessed in 2010, which was abundant in rainfall and mean air temperature was by 0.2°C lower in comparison with 2009. Much lower protein amounts (12.54%) were found in grain from 2008, when the mean air temperature and rainfall total were the lowest over the whole analyzed period. Among the compared wheat cultivars, Bombona revealed a significantly bigger protein accumulation in grain but yielded markedly lower than Tybalt.

Applied nitrogen doses led to a systematic increase in grain protein concentrations in the range from 13.06 (60 kg N∙ha^-1) to 15.18% when the highest 150 kg N∙ha^-1 nitrogen dose was supplied (Tab. 4). Also results of other researcher to an increase in total protein concentrations in effect of bigger nitrogen fertilization [1, 2, 3, 22]. Results evidencing a lack of response to the level of nitrogen fertilization are also encountered in the literature of the subject [2], a diminished protein content at higher nitrogen fertilization is also quoted in the literature [25]. Protein concentrations in grain of the studied cultivars depended on the weather conditions. Significantly bigger amount of this component was assessed in Bombona c.v. grain in 2008, which was characterized by the lowest amount of rainfall during spring wheat vegetation period. In the subsequent years with higher precipitation total, the cultivars did not reveal any marked diversification regarding this feature. Wheat cultivars similarly responded to nitrogen fertilization dose (Tab. 4). However, a cooperative effect of fertilization with the weather course on protein accumulation in grain was observed (Fig. 4).

CONCLUSION

1. Nitrogen fertilization caused a significant increase in grain yield to the dose of 90 kg N, at which the highest (4.51 t∙ha^-1) grain yield was produced. Bigger doses of 120 and 150 kg did not lead to increased yielding, on the contrary, a declining tendency was observed in the level of spring wheat yields.
2. Diversified weather conditions over the period of the experiment and cultivar factor affected spring wheat yielding level. The greatest grain yield, on average 4.31 t∙ha^-1 was produced in 2009, with similar to average rainfall amount and the highest air temperature. On the other hand, the lowest 4.10 t∙ha^-1was obtained in 2010, very wet year and abundant in rainfall.
3. The level of nitrogen fertilization influenced an increase in ear number per area unit and 1000 grain weight up to the dose of 60 kg N∙ha^-1. Among the yield components only the number of ears per area unit depended on the weather conditions. The number of grains per ear and 1000 grain weight, similar as the number of ears depended on the cultivar.
4. Protein content in grain depended on the weather conditions, nitrogen fertilization level and the cultivar. Applied nitrogen doses caused an increase in protein concentrations in grain within the range from 13.06 to 15.18% when the biggest, 150 kg N∙ha^-1 dose was supplied. Among the compared wheat cultivars Bombona was characterized by the greatest protein accumulation in grain.

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Accepted for print: 03.04.2014

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