Analysis of wheat genotypes and N application on the yield in response to protein and nitrogen content in grains and straw

Nitrogen plays an important role in protein formation, cell improvement and other physiological and agronomical activities, while genotypes also play an important role in increasing yield because different genotypes have different performance. This research mainly focuses on nitrogen application and genotypes performance in wheat production. Nitrogen application showed significant variation for all parameters and produced maximum tiller m (366), grains spike (52.5), biological yield (11775 kg ha), grain yield (4009 kg ha), nitrogen concentration in straw (0.50 %), protein concentration in straw (2.84 %), nitrogen concentration in grains (2.01 %) and protein concentration in grains (11.5 %) with nitrogen applied at the rate of 150 kg ha while 120 kg nitrogen ha gave maximum leaf area index (4.4 cm) and thousand grains weight (40.1 g). Genotypes showed differentiation for all parameters recorded during the experiment except nitrogen and protein content in grains and straw while between different genotypes, wheat genotype Pirsabak-2013 performed better and produced good performance and produce maximum tillers m (372), grains spike (52), leaf area index (4.4 cm), thousand grains weight (40.4 g), biological yield (10767 kg ha) and grain yield (3658 kg ha). Interaction between nitrogen application and wheat genotypes significantly differed tiller m, leaf area index, thousand grains weight and biological yield. Wheat genotype Pirsabak-2013 with nitrogen applications 120 up to 150 kg ha enhanced grain yield, protein content, nitrogen content and could be recommended for qualitative and quantitative production in wheat.

Wheat was cultivated on about 9.25 million ha area with total production of 25.5 million tons, having an average yield of 2873 kg ha -1 while in the Khyber Pakhtunkhwa province area under cultivation was 0.75 million hectare having production of about 1.4 million tons with the average yield of 2359 kg ha -1 [2]. In Asia, Pakistan represents as a third largest producer of wheat where annual consumption of wheat is around 23 million tons that will leave the country with a surplus of a few tons that can be exported [3, 4]. There are different reasons for low production of wheat in Pakistan and this yield production gap of wheat in the country need to be occupied by increasing yield per unit area. Collective use of fertilizers is very important, as the proper combination of chemical fertilizers can increase the yield of wheat by 50% [5]. Most of these are associated with the nutrient management flaws. Among nutrient management aspects, unoptimistic application of nitrogen has a significant role to influence the crop productivity [6]. Nitrogen is vital in crop productivity, which plays an important role in accelerating yield and gave optimum economic return and its deficiency will constitute in low yield and productivity in cereal crops [7]. Nitrogen is the most important component of chlorophyll and its absence in soil effect the availability of phosphorus, potash and other nutrients [8]. Nitrogen is vital in crop productivity which plays an important role in accelerating yield and gave optimum economic return and its deficiency will result in low yield and productivity [9]. Application of nitrogen has a great importance and considered the best and appropriate for production in wheat and maize [10]. Throughout the world, nitrogen is believed to be the second most limiting factor in wheat crop production and it limits production in non-fertilized agriculture [11]. In the early growth stages of wheat crop, an adequate supply of nitrogen fertilizer in the form of urea is very important for the initiation of leaves and florets [12]. Among the compounds which play role in the process of photosynthesis, nitrogen is an important part of their composition. Stimulation of root development as well as absorption of important nutrients is stimulated by nitrogen. Nitrogen acts as a limiting variable for crop production. Therefore, its application results higher biomass yields. Protein concentration in plant tissues and kernel integrity can be improved by increasing nitrogen supply. The quality of yield in terms of milling and vegetative growth is notably enhanced by applying nitrogen.
[13]. Nitrogen being an essential macronutrient, influences the yield of wheat in a significant way by effecting forage as well as production of grains. [14]. Nitrogen application improves different wheat crop parameters like thousand grains weight [15,16], tillers m -2 , grain yield, more productive tillers, spikes m -2 , grains spike -1 and biological yield [17]. Grain weight is controlled genetically which is greatly impacted by environmental factors during the process of grain filling. Nitrogen is generally the most confining nutrient for irrigated and rainfall wheat production area and as such nitrogen fertilizer is always needed to attain desired yield and protein content [18]. Nitrogen is effective in all components of plant yield including number and weight of grain. Lack of this element reduces economic output of the crop and higher amount of it increases vulnerability of plant to load and diseases [19]. Production of high yielding wheat genotypes mostly increase by increasing level of nitrogen [20]. Application of adequate amount of nitrogen increase seed development, grain filling rate and maturity duration, which finally produce highest grain weight [21]. In addition to the formation of proteins in wheat grains and straw, N is an important and core part of plant chlorophyll which is the primary light energy absorber for photosynthesis. An adequate provision of N is linked with vigorous vegetative growth and high photosynthetic activity and its optimum supply influences the utilization of carbohydrates. Nitrogen is proven beneficial at certain growth stages for many genotypes, its application during grain filling stage is required to get more grain yield [22]. All active processes in plant are connected with protein of which nitrogen is an important constituent. Consequently, to get more crop production, nitrogen application is essential in the form of chemical fertilizer. Nitrogen fertilizer is known to affect the number of tillers m -2 , spikelet's per spike -1 , Grains spike -1 , spike length and thousand grain weight [23]. Nitrogen plays a key role in maximizing the crop production [24] and enhances the yield as well as quality of all crops [25,26]. Additionally, when N applied at higher rate it increases photosynthetic processes in plant, leaf area production, leaf area duration (LAD) as well as net assimilation rate (NAR) [27]. Due to unavailability of broad genetic diverse genotypes, the average yield of wheat in Khyber Pakhtunkhwa province (1807 kg ha -1 ) is a lot lower than the national average production (2787 kg ha -1 ). As population increase in Pakistan, the demands of wheat is continuously increasing day by day. In order to fulfil this demand of population and overcome future food shortage, high yielding genotypes and disease resistant genotypes of wheat are required to introduce. For this purpose, wheat genotypes with broad genetic background should be developed [28]. Genotypic characteristic of the genotypes is very important to increase different yield traits because different genotypes had different characteristics at different climatic region [29]. The plant breeding scientists are actively involved in developing of drought resistance and disease resistance wheat genotypes that produce higher grain yield per hectare. A number of different wheat genotypes are released till now by various researchers and institutions but their comparative study is still absent in the literature. The released and approved high yielding wheat genotypes are conceivably examined in the local climate of the area but their performance with climate change impact of the local weather and sowing time is still a big issue to be tackled properly [30]. Keeping in view the significant role of nitrogen and genotype selection, the present study was planned to find effect of wheat genotypes and nitrogen application on the yield in response to protein and nitrogen content in grains and straw.

Materials and methods
A field study entitled "Analysis of wheat genotypes and N application on the yield in response to protein and nitrogen content in grains and straw" was conducted at Bacha Khan Agricultural Research Farm (BARF), Bacha Khan University Charsadda-Pakistan during 2015-16. The experiment was done according to Randomized Complete Block (RCB) Design having three replications with plot size of 3m x 1.8m. Two factors were studied, i.e. nitrogen levels (80, 120 and 150 kg ha -1 ) and genotypes (Pirsabak-2013, Faisalabad and Shahkar). Recommended dose of phosphorus 90 kg ha -1 was applied to all plots uniformly and other agronomic and cultural practices were uniformly maintained. Field data was recorded on tillers m -2 , grain spike -1 , leaf area index, thousand grains weight (g), biological yield (kg ha -1 ) and grain yield (kg ha -1 ), while Lab data was recorded on nitrogen concentration in straw, protein concentration in straw, nitrogen concentration in grains and protein concentration in grains. Results and discussion Tillers m -2 Nitrogen, genotypes and interaction N x G considerably affected tillers m -2 as showed in (Table 1). Tillers m -2 was affected positively by increasing the application rate of nitrogen.
Maximum (366) tillers m -2 were produced when N was applied at the rate of 150 kg ha -1 as compared to 80 and 120 kg ha -1 . Increasing in rate of N can enhance tillers m -2 reported by [31,32]. Among various genotypes, Pirsabak-2013 produced maximum (372) tillers m -2 as compared to other genotypes. This might be due to the genetic difference and its interaction with environmental factors. These factors are responsible for significant variation in wheat tillers m -2 among different wheat genotypes [33]. In case of interaction N x G, wheat genotype Pirsabak-2013 with nitrogen 150 kg ha -1 gave maximum (403) tillers m -2 as compared to all other possible interaction as shown in (Fig. 1). Grains spike -1 Nitrogen and genotypes had significant impact on grain spike -1 , however interaction N x G had no significant impact as presented in (Table 1). Nitrogen application up to 150 kg ha -1 enhanced grains spike -1 and produced maximum (52.5) grains spike -1 , while minimum grains spike -1 (43.2) were recorded when N applied at the rate of 80 kg ha -1 . The results are in accordance with those of [32, 34] who described that grains in spike were increased by N application up to 120 and 150 kg ha -1 . Among different wheat genotypes, Pirsabak-2013 produced maximum (52.0) grains spike -1 as compared to others wheat genotypes. The variation in number of grains spike -1 between genotypes might be genetic. Similar finding was reported by [35] who showed variations among different wheat genotypes for grains spike -1 . Leaf Area index (cm -2 ) Various nitrogen levels, wheat genotypes and their combination N x G had significant effect on leaf area index (LAI) as presented in (Table 1). Nitrogen varied LAI significantly and maximum mean value (4.4 cm -2 ) was noted with 120 kg N ha -1 , while minimum LAI (3.9 cm -2 ) was recorded with 80 kg ha -1 . Among different wheat genotypes, maximum LAI (4.4 cm -2 ) was recorded by Pirsabak-2013, while minimum (3.8 cm -2 ) was recorded by Shahkar. The variation for LAI is the reason of inheritance differentiation among genotypes. The same results were found by [36,37]. In case of interaction, N x G maximum LAI (4.6 cm -2 ) was recorded by Pirsabak-2103 with 120 kg N ha -1 as shown in (Fig. 2). Nitrogen enhances growth and consequently leaf area expansion. Same results of positive effect of N application on the LAI were reported by [38].

. Leaf area index as affected by interaction of different wheat genotypes and nitrogen levels Thousand grains weight (g)
Weight of grains is a key part of final yield. It was revealed that wheat genotypes, nitrogen and their combination N x G had significant effect on thousand grains weight as presented in (Table 2). Nitrogen enhanced grains weight and maximum thousand grains weight (40.1 g) was recorded with nitrogen 120 kg ha -1 , while 80 kg ha -1 gave minimum  Leaf ara index (cm2) Linear (Leaf ara index (cm2)) weight (42.1 g) was recorded by Pirsabak-2013 with nitrogen 120 kg ha -1 as presented in (Fig. 3) (Fig. 3). The difference we got in biological yield between wheat genotypes may be the genetic variability and other ecological factors. [36, 39] elaborated considerable differences in biological yield of wheat among different wheat cultivars. Grain yield (kg ha -1 ) Grain yield is the main goal of any study, a significant fluctuation in grain yield of wheat genotypes was indicated by various N levels as shown in (Table 2). Different nitrogen levels varied grain yield and maximum grain yield (4009 kg ha -1 ) was produced with 150 kg N ha -1 , while minimum amount of grain yield (2934 kg ha -1 ) was produced with nitrogen 80 kg ha -1 . The findings from this experiment are alike with [32,40] reported that yield of wheat improved by the application of nitrogen 150 kg ha -1 . Maximum grain yield (3658 kg ha -1 ) was produced by Pirsabak-2013 as compare to Faisalabad and Shahkar. The difference in grain yield within wheat genotypes may be due to the genetic variation in wheat cultivars and may be other ecological and environmental factors [37]. Our results are also in accordance with the investigations of [36] who found clear variation in the grain yield of different wheat genotypes.

. Thousand grains weight (g) and biological yield as affected by interaction of different wheat genotypes and nitrogen levels Nitrogen Content in Straw (%)
It's confirmed from the findings that the application of nitrogen showed clear variation for N content in straw while genotypes and interaction N x G showed no effect on N content in straw as presented in (Fig. 4). Nitrogen content was increased by increasing nitrogen level and maximum N content in straw (0.50 %) was noted with 150 kg ha -1 while minimum (0.42 %) N in straw was noted with 80 kg ha -1 . These findings agree with those reported by [41,42].

Protein Content in Straw (%)
Analysis showed variation for protein content in straw by the application of nitrogen while wheat genotypes and interaction N x G showed no effect as shown in (Fig. 4).
Increasing the rate of nitrogen increased the mean value for protein content in straw and produced maximum (2.84 %) protein percent in straw, while decreasing the level of nitrogen to 80 kg ha -1 gave minimum (2.41 %) protein content in straw. The result is supported by [43] giving the same result in term of P content in straw and grain.

Nitrogen Content in Grains (%)
The application of various nitrogen levels showed variation for N content in grains while wheat genotypes and interaction N x G showed no variation as figure out in (Fig. 5). By increasing level of nitrogen up to 150 kg ha -1 gave maximum (2.01 %) nitrogen content in grains, while minimum dose of 80 kg N ha -1 gave minimum mean value of (1.79 %) N content in grain. The result is supported by the finding of [43] giving the same statement about N and P content in grains of wheat crop.

Protein Content in Grains (%)
Protein content in wheat grains as influence by different wheat genotypes and nitrogen treatments data is presented in (Fig. 5). The application of nitrogen is directly proportional to the protein content in grains and increasing the rate of nitrogen increased the means value of protein content in grains, while different wheat genotypes and interaction N x G showed no effect. Maximum mean value (11.5 %) protein content in grains was noted by the application of N at 150 kg ha -1 while minimum protein (10.2 %) was marked with 80 kg N ha -1 . The same finding was observed by [41][42][43] giving the same situation for N and P content in grains and straw.