Effects of Varying Seed Rates on Yield Performance of Winter Wheat Cultivars

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Published on International Journal of Agriculture & Agribusiness
Publication Date: July 5, 2019

Baya Forward, Mango Lawrence & Kugedera Andrew Tapiwa
Department of Agriculture Management, Faculty of Agriculture, Zimbabwe Open University, Bindura
Department of Livestock, Wildlife and Fisheries, Gary Magadzire School of Agriculture and Natural Sciences, Great Zimbabwe University, P. O. Box 1235 Masvingo

Journal Full Text PDF: Effects of Varying Seed Rates on Yield Performance of Winter Wheat Cultivars (Panmure Research Station: A Case of Shamva District).

Abstract
A field experiment was conducted to study the effects of seed rates and variety on yield and yield components of winter wheat (Triticum aestivum. L) at Panmure Experiment Station, Shamva District during 2018 winter cropping season. Six levels of seed rates (60; 80; 100; 120; 140 and 160 kg ha-1) and three varieties (Dande, Kana and Ncema) were tested. The experiment was laid out as a randomized complete block design (RCBD) and was replicated three times. Phenological growth, yield and yield related data were collected and their ANOVA was analyzed using Cropstat version 7.0 and where treatment means were significantly different, they were separated using the Least Significant Difference (LSD) at 5% probability level. The results showed that using different seed rates on different varieties had significant effects. Only five parameters that include days to anthesis (flowering), days to physiological maturity, plant height, stem lodged plants and number of effective tillers per net plot had significant effect on different seed rates. However ear length and average tillers per plot had no significant effects to seed rates. The interaction of seed rates and varieties also showed no significant difference (p = 0.363) on grain yield. However, Kana had the highest yield of 2927.5 kg ha-1 and this was achieved at 32g/plot (80 kg ha-1) seed rate. There was significance (p < 0.01) interaction between variety and seed rates with regard to anthesis time. Dande was the first to reach anthesis at day 59, under seed rate of 40g/plot (110 kg ha-1) and 64g/plot (160 kg ha-1). There were significant (p < 0.01) interactive effects of variety and seed rate with regard to physiological maturity. Ncema variety elicited earliest maturity, reaching physiological maturity at day 116 after emergence and this was achieved under seed rate of 24g/ plot (60 kg ha-1) seed rate. However, further studies have to be done under different soils using higher seed rates more than 160 kg ha-1 and reducing the inter row spacing from 0.25m to 0.2m in order to exploit the recommendation of the present study.

Keyword: Experiment, effects of seed rates, variety on yield, yield components, winter wheat, varieties, Dande, Kana & Ncema.

1. Introduction
Agriculture is the mainstay of the Zimbabwean economy providing livelihoods to approximately 70% of the population, contributing between 15% and 20% of Gross Domestic Product (GDP) and providing 40% of export earnings and supplying 63% of agro-industrial raw materials (Kapuya, Jongwe and Saruchera, 2010). This makes the agricultural sector strategic and very important sector in designing strategies and policies to reduce poverty, reduce food insecurity and boost rural incomes. Zimbabwe Central Statistical Office (ZIMSTAT) (2012), published a report on how wheat (Triticum aestivum. L) is the second most important strategic food security crop in Zimbabwe after maize. Wheat has become a staple crop given its high demand for bread and other confectioneries. Wheat farming is a major cropping activity and the commodity is highly valued particularly its product, bread. Bread has become a key staple food in Zimbabwe thus making wheat the second most important crop after maize, Kapuya et al. (2010). Wheat contributes about four percent to the GDP of Zimbabwe (Reserve Bank of Zimbabwe (RBZ), 2009). The immediate wheat products are flour and bran. Flour is the main ingredient for making bread and other confectionaries consumed daily by mostly urban Zimbabweans while wheat bran is mainly used in the stock feeds manufacturing sector.
Zimbabwe like most low-income countries has a high proportion of their population dependant on agriculture for their means of livelihood. Therefore what happens in the sector is critically important in determining economic development of the country. The farmers who are also the major consumers are doing well, this has a positive impact on the development of agro-processors and the demand for goods produced in the non-agriculture sector (Anseeus and Davies, 2011). This research will focus on the varying seed rates effects on yield performance across three spring wheat varieties namely Dande, Kana and Ncema at Panmure Experiment Station, Shamva district, Mashonaland central province in Zimbabwe. This research is trying to address the continued decline in wheat yield. There are so many reasons behind the decline in wheat yield and seed rate is one of the contributing agronomic factors. Optimum seeding rate is considered an important management factor for improving yield of any crop but this study mainly focuses on wheat. It is of particular importance in wheat production because it is under the farmer’s control in most cropping systems (Hussain, Ali and Ahmad, 2012). Since cultivars genetically differ for yield components, individual cultivars need to be tested at a wide range of seeding rates to determine their optimum seeding rate (Wiersma, 2002). Previous research shows that seeding rates significantly affected biological yield, Hussain et al. (2012), spike number and weight (Ozturk, Caglar and Bulut, 2006). Higher seeding rates compensate for reduced tiller development and promote more main stem spikes which can be favourable, especially for cultivars that tend to produce fewer tillers (Gafaar, 2007); Rana, Ganga and Pachuri, 2005). A close relationship exists between wheat stands and yield components (Kumar, Singh and Thakur, 2011). According to Ozturk et al. (2006), too much competition, even among wheat plants, may lead to fewer grains per spike and lower grain weight. The key is to get an optimum plant population with uniform distribution for efficient use of available resources. This study was designed to provide a comprehensive understanding of the effects of varying seed rates on yield potential of selected varieties. Currently, there is lack of detailed and consolidated information in the Shamva area concerning the optimum seed rates for the winter varieties.

2. Methodology
2.1 Research site
The study was conducted at Panmure Experiment Station in Shamva and is 95 km from Harare on the North Eastern side at a 1ongitude 31o47’E and latitude 17o16’S. The altitude is 881 metres above sea level (m.a.s.l). The area falls under natural region IIB with an average rainfall of between 700-900 mm annually, mean maximum temperature of 30oC and mean minimum of 15oC with ground temperature reaching about -15oC with soils predominantly reddish brown, medium grained loamy and sandy loams prone to capping problems.

2.2 Plant varieties
Three wheat cultivars (Dande, Ncema and Kana) were used (Table 3.1). The three wheat cultivars were medium maturing varieties which have nearly similar days to reach physiological maturity and yield potential. The normal statured Dande variety has a yield potential of 2.8 t/ha and matures in 125 – 130 days. Ncema variety has a yield potential of 2.5 t/ha and matures between 125 and 130 days and Kana has yield potential of 3t/ha maturing between 115 and 125 days.

Table 1: Germplasm used and their sources

2.3 Experimental design
The experimental design was randomized complete block design (RCBD), replicated three times. Three wheat varieties namely Dande, Kana and Ncema were assigned to the main plots with six treatments or six seed rates levels per each cultivar, (Appendix 11).

Table 2. Allocation of treatments

2.4 Land Preparation
The land was prepared using a tractor drawn disk plough in early April 2018. Secondary tillage operations such as discing and rolling were carried out in order to produce a fine tilth and to get rid of early weeds and levelling off the field plots to avoid bias. Maize was the previous crop planted on that block.

2.5 Planting
Wheat was planted by on the 5th of May 2018; planting was done using the drilling method in rows spaced 25 cm apart. Seed was drilled by hand and covered with a thin layer of soil. Furrows were opened using a hoe. The rows were at 0,25m inter row spacing and seed planted at a specified seed rate per hectare according to the treatment. The planting depth was 3-5cm using the drilling method. The distance between plots along the rows was 0.5m. The distance from one replicate to the other was 1m. Each replicate had 18 plots and total plots were 54, whereby each gross plot had an area measurement of 3.5m2(8 rows). Gross plot size was 8 rows, 1.75m width and 2 m row length.

2.6 Fertilization
Fertilizer rates of 400kg/ha Compound D at 7-14-7 (0.53 – 1.06 – 0.53) NPK kg/ trial area and drilled in the rows at uniform rate. Fertilizer was drilled by hand in the furrows and stirred to mix with soil to avoid seed scorch by the 7% N in compound D Top dressing was applied at 400kg/ha Ammonium Nitrate (AN) 34.5% (2.61 kg/trial) was split applied after irrigations in equal amount. The first split of ammonium (AN) was applied at six weeks after the time of emergence and second split was applied four weeks later.

2.7 Irrigation management
The crop was subsequently irrigated as per need of the crop and soil during growth and development. All irrigation cycles were applied at uniform rate for all the treatments. The crop was subsequently irrigated as per need of the crop and soil during growth and development. From first irrigation to plant physiological maturity, 10 irrigation cycles were applied at total irrigation was 524.7mm.

2.8 Weeds Control
Mainly broad leaved weeds like gallant soldier (Gallinsoga parviflora) and black jack (Bidens pilosa) were found and these were controlled by an herbicide called 2-Methyl-4 Chlorophenoxyacetic Acid (MCPA) for reducing weed-crop competition once before the canopy closure. At a later stage weeds were controlled manually using hoes and hand pulling.

2.9 Pests Control
Leaf eaters were the first pests to be observed feeding on wheat leaves at 4 weeks after crop emergency (WACE). These pests did not inflict much damage to the photosynthetic machinery of wheat. A formulation of Carbaryl 40 wetable powder (WP) was applied at the rate of 1 kg/ha to control the leaf eaters.

2.10 Diseases Control
Wheat rust was visually assessed and scored where all three varieties had less than five percent that means they were tolerant to the disease. Therefore no disease control which was done.

2.11 Data collection
Data was collected using different parameters as discussed in the sections below.

2.12 Phenological parameters
Days to 50% flowering (anthesis)
Anthesis was recorded when the ears or panicles where small, white flowers were fully visible or produced pollen tubes. The plants reaching 50% flowering from each plot were determined by visual observation and recorded.

Days to 90% physiological maturity
Days to physiological maturity were recorded by counting the number of days from day of emergence until when 90% of the plants changed from green colour to yellowish, for which it had lost its water content due to physiological maturity.

2.13 Vegetative growth parameters
Plant height (cm)
The average height of ten randomly selected plants from the net plot area of each plot was measured in centimetres from the ground to the top of spike, excluding awns at maturity. The means were recorded.

Effective Tiller Numbers
The numbers of effective (fertile) tillers per 1m2 were counted from each plot at harvesting.

Number of lodged plants per net plot
Total number of lodged plants per net plot were counted and recorded at harvesting.

2.14 Yield and yield related parameters
Ear length (cm)
Ear length was measured from ten randomly selected plants of the inner rows in centimetres and the mean length was recorded on each plot by measuring from the base to the upper most part of the spike.

Average number of ears per plant
Numbers of productive ears per plant were counted from ten randomly selected plants from the inner rows of each plot and the mean ear number was recorded.

Total number of tillers per net plot
The total numbers of productive spikes per net plot were counted at harvesting.

Grain yield (kg)
Grain yield was measured by taking the weight of the grains threshed from the net plot area of each plot and converted to kilograms.

Moisture content (%)
Grain moisture was measured by taking the moisture of the grains threshed from the net plot area of each plot in percentage.

Harvesting
Harvesting was done on the 10th of October 2018. A net plot of four rows (middle) measuring 2m2 was harvested, after discarding two rows on either side. It was carried out sequentially, beginning with plot one up to the last plot number (54). Sickles were used to cut the above ground biomass of wheat ears and put into harvesting bags.

Grain processing
Each harvested plot was threshed and winnowed at the sheds, then weighing of grain was done using digital scale and lastly taking moisture of each sample using a moisture meter. All the data was recorded for each process done.

2.15 Data presentation
The data was presented using bar graphs on grain yield, plant height and tillers per plant. Line graphs were used to interpret the data for days to physiological maturity, anthesis and stem lodging.

2.16 Statistical Analysis
Data was analysed using Cropstat version 7.0 and where treatment means were significantly different; they were separated using the Least Significant Difference (LSD) at 5% probability level.

3. Results and Discussion
3.1 Grain yield
Wheat variety and seed rate treatments had no combined effect (p = 0.363) on grain yield (Figure 1). However, significant (p < 0.01) effects were recorded on the main parameters of variety which include plant height, anthesis, stem lodging, days to physiological maturity and tillers per plant. Seed rate main effect was not significant (p < 0.061). Kana had the highest yield of 2927.5 kg ha-1and this was achieved at a seed rate of 32g/plot. This current result differs with those of Hameed et al. (2003) and Ijaz et al. (2002), who reported that grain yield increased as seed rate increased. The interaction of seed rate and ear length was not statistically significant. There is contrast on findings from Hussain et al. (2012) and Awdie, Singh and McCaig (2008) reported that grain yield increased as seeding rate was increased from 50 to 150 kg ha-1 and from 100 to 150 kg ha-1, respectively. Moreover, Ali et al. (2010) concluded that the three years average data showed that grain yield was higher at seeding rate of 150 kg ha-1 followed by 175 and 200 kg ha-1 as against the seeding rate of 125 kg ha-1. The same result was also reported by Iqbal et al. (2010) who concluded that seeding rate of 150 kg ha-1 produced significantly higher grain yield (4120 kg ha-1) followed by 175 and 200 kg ha-1 seeding rates (3904 and 3785 kg ha-1). However, seeding rate of 125 kg produced significantly lower grain yield (3.669 t). Report by Nazir et al. (2000) also showed that 150 kg ha-1 seeding rate produced significantly the highest grain yield. Likewise, Jemal et al. (2015) also reported that Shorima and Kakaba varieties gave maximum grain yield at seeding rate of 150 kg ha-1 and Digalu variety produced highest yield at seeding rate of 175 kg ha-1 as compared to 100; 125; and 200kg ha-1. Seleiman et al. (2010) also confirmed that increasing seeding rates up to350 or 400 grains m-2 increased grain yield. Higher grain yield with higher seeding rates was also reported by Olsen et al. (2005); Haile and Girma, (2010). The same result was also confirmed by Sikander et al. (2003) who concluded that increasing seeding rate from 150 – 250 seeds/m2 resulted in higher grain yield. Figure 1: Effects of Seed rate on yield of wheat varieties. Vertical bars represent standard error bars of means 3.2 Days to anthesis There was a significant (p < 0.01) interaction between variety and seed rate with regard to anthesis time. Dande was the first one to reach anthesis at day 59, under 40g (100 kg ha-1) and 64g (160 kg ha-1) seed rate. Ncema was the last flowering variety, reaching anthesis at 67 days under 24g (60 kg ha-1) seed rate (Figure 2). Kana exhibited intermediate performance, with an average of 62 days to anthesis across all seed rates. As the seed rates increased across all varieties (Dande, Kana and Ncema), the days to anthesis were decreasing. This was due to high competition for sunlight, nutrients and moisture between plants which accelerated to the days to flowering. It is critical to match variety and sowing time to ensure flowering occurs during the optimal flowering window to maximise grain yield potential. This finding was also confirmed by Gafaar (2007) who indicated that increasing sowing density from 200 up to 400 grains per meter square in wheat crop significantly decreased the number of days to 50% flowering. Another research finding on the effect of seeding rate also revealed the same results of flowering being affected by higher seeding rates (Iqbal et al. 2010). Furthermore, Awdie et al. (2008) concluded that increasing the levels of seeding rates decreased the days to flowering consistently. The optimum flowering window is determined by a balance in water used during canopy development and water used during the grain formation and grain-filling phases (Hussain, Ali and Ahmed, 2012). Crops that flower too early have increased risk of frost damage, while crops which flower too late have increased risk of high temperatures and water deficit which can restrict grain formation and grain-filling. In vernalisation, there is a responsive within varieties following saturation of long days where there is hasten progressive inflorescence development and stem elongation. Vernalisation is essentially the prerequisite for long days to reduce the time to flowering (Bryan, 2011). According to Park et al. (2003), Optimum seeding rates for grain yield of winter cereals may be higher when seeding is delayed past the optimum date of seeding. Higher seeding rates increase early days to maturity and weed competitiveness, but may have negligible or negative impacts on grain yield due to increased interplant competition. Figure 2: Interactive effects of variety and seed rate on days to anthesis 3.3 Days to physiological maturity Days to 90% physiological maturity showed significant (p < 0.01) interaction effects of variety and seed rate in relation to physiological maturity. Ncema variety elicited earliest maturity, reaching physiological maturity at day 116 after emergence and this was achieved under 24g (60 kg ha-1) seed rate. Dande recorded relatively late maturity, reaching physiological maturity at day 129 at 24g (60 kg ha-1) after emergence (Figure 3). Increasing seeding rate from 24g (60 kg ha-1) to 64g (160 kg ha-1) decreased days to 90% maturity on Dande and Kana. The highest seeding rates on these two varieties associated with early maturity might be due to plant competition for available resources that include moisture, sunlight and nutrients. The result was in agreement with Seleiman et al. (2010) who reported that increasing seeding rates from 250 – 400 m–2 grains prolong the number of days from sowing to maturity of wheat. The present finding showed that as seeding rate decreases from 64g to 24g/plot, days to physiological maturity increased from 121 to 129 days (Figure 3). Similar with the present finding by Awdie et al. (2008) also noted that increasing the levels of seeding rate hastened physiological maturity of bread wheat. Furthermore, Bryan (2011) indicated that increasing levels of seeding rate promoted early physiological maturity on different cultivars of wheat. In conformity with the present result by Hassanein (2014) reported that, differences in maturity can be caused by the combined effect of genetic and environmental factors during their growth and grain filling of the crops. However the result was in contrast with the findings from Osman and Mohamed (2011) who reported that abundant supply of seed rates delay physiological maturity in wheat. This is due to luxurious growth at the expense of flowering where there is ranky growth; plants compete for nutrients and sunlight. Figure 3 Interactive effects of variety and seed rate of plant physioloogical maturity. 3.4 Plant height (cm) The analysis of variance indicated that the main effects of variety were not significant (p > 0.08) to the plant height; however in contrast, the seed rates were significant (p < 0.01) to the plant height (Figure 4). Kana scored the greatest height of 90 cm under 40g seed rate. Ncema was the shortest, with 72 cm under 32g (80 kg ha-1) seed rate (Figure 4 c). Overally, Kana had the highest average plant height across all seed rates (84.5 cm). Similar with the present finding, Soomro et al. (2009) noted that wheat sown at higher seeding rate produced greater plant height as shown by Dande at 56g/plot, followed by 64g/plot, but their findings differed with Ncema and Kana across all seed rates. Another research finding by Awdie et al. (2008) also concluded that plant height increased consistently with increasing seeding rate. Rahim et al. (2012) also reported that the significant difference on plant densities of 450 and 300 plants m2 with highest and lowest plant height, respectively. Other researchers also reported in wheat that the height of plants grown at the lowest seeding rate was significantly lower than the height of plants grown at higher seeding rates (Spink et al. 2014; Ghulam et al. 2011). Moreover, this result was in harmony with the finding of Fani et al. (2014) who indicated that with increasing density, plant height slightly increases and there after decreases could be attributed to restrictions on plant food sources. Height of the crop is mainly controlled by the genetic makeup of a genotype and it can also be affected by the environmental factors (Mennan and Zandstra, 2005). Figure 4: Main effects of seed rate on plant height of varieties- a) Dande; b) Kana and c) Ncema. Stem lodging There was significant (p < 0.01) interaction between seed rate and variety, however the main effects of seed rate and variety were not significant (p = 0.786; p =0.122, respectively). Highest lodging for every variety was recorded under 64g seed rate (Figure 5). Lodging was zero under 24g seed rate for all varieties. The current findings have highlighted that stem lodging increases with an increase in the seed rate. These results are congruent with findings observed by Monsanto (2015) in soyabean. Higher seeding rate caused lodging due to stem thickness because of the lower light penetrating into the plants canopy bed and more inter specific competition to more absorption light. Higher seeding rate and lower light penetration influences increase of inter node length, reducing stem thickness and increasing plant height (Otteson et al. 2007). Increasing seed rate results in increased plant populations hence plants are prone to compete for resources and there is high likelihood of stunted growth and weak stems. According to Spink et al. (2014), winter wheat is capable of compensating among yield components, which often results in similar grain yields being produced across a fairly wide range of seeding rates. However, using seeding rates that are too low can lead to excessive tillering. This may also delay maturity, increase weed competition, and fail to make use of the plant’s full yield potential. Using rates that are too high may increase costs, result in increased lodging, and possibly reduce yields. Too much competition, even among small grain plants, may lead to fewer kernels per head and lower kernel weight. The key is to get an optimum plant population with uniform distribution for efficient use of available resources.