Abstract: A field experiment was conducted at the University of Zabol, The experimental farm in Southeast of Iran during 2007-08 to investigate the impacts of nitrogen (N) rate and plant density of maize (Zea mays L.) c.v. K.S.C 704. Split plot experimental treatments comprising three plant densities under title subplot included (P1 = 60,000 plants ha-1, P2 = 80,000 plants ha-1 and P3 = 100000 plants ha-1) and Four nitrogen rates (N1 = 200 kg ha-1, N2 = 250 kg ha-1, N3 = 300 kg ha-1 and N4 = 350 kg ha-1) were kept in main plots. Maize produced significantly as well as grain yield at high than at low density. Grain yield and Photosynthesis Active Radiation (PAR) absorption increase with increasing N rate and the highest amount of grain yield were obtained at N4 treatments. Grain yield and PAR absorption increase with increasing plant density and the highest amount of grain yield were obtained at P3 treatment. It is concluded that growing maize at high density with application of 350 kg h-1 N rate that could result in maximum Grain yield of maize and hence increase productivity of maize crop.
INTRODUCTION
Maize (Zea maize L.) is the third most important cereal crop of the world. It is used as food, feed and forage. Maize is the most suitable fodder crop for silage. Therefore, it is called the king of crops suitable for silage (Muhammad et al., 1990).
Management of corn (Zea mays L.) row spacing and crowed has been used to increase corn productivity. Widdicombe and Thelen (2002) recorded yield increases up to 10% with reducing row spacing. Murphy et al. (1996) showed that corn planted at 50 cm rows intercepted about 8% more PAR at silking than crop at conventional rows, reducing biomass of late-emerging. Nitrogen fertilizer is universally accepted as a key component to high yield and optimum economic return as it plays a very important part in crop productivity (Ahmad, 2000) and its deficiency constitutes one of the major yield limiting factors for cereal production (Shah et al., 2003). Increasing plant density for short season maize increases cumulative intercepted PAR, which compensates for a short growing season to achieve high yield with substantially less irrigation (Edwards et al., 2005). The difference in the dry matter accumulation in maize is attributed to post-silking N uptake and it improves with increase in N rate (Rajcan and Tollenaar, 1999). Differences in biological yield and N uptake varied partly due to decreased soil N mineralization and partly due to the drier weather conditions of different years and N uptake rate has been found to assist the improvement of dry matter yield in the plant (Greef et al., 1999). Adequate planting densities can contribute towards significant grain yield increases for farmers (Cardwell, 1992). Because corn or maize yield response to density depends on genotypic (Chandra and Gautan, 1997) and environmental factors (Bondavalli et al., 1970) and even negative responses of the crop to a given factor can be verified beyond certain limits. Its biomass yield increases with increase in plant density and N rate (Gaurkar and Bharad, 1998). Hamid and Nasab (2001) reported that both economical and biological yields are correlated with vegetative and reproductive phase duration in maize. Leaf area influence interception and utilization of solar radiation of crop canopies and consequently maize dry matter accumulation and economical yield. Leaf area and number are important factors in the estimation of canopy photosynthesis in crop growth simulation models that compute dry matter accumulation from temporal integration of canopies photosynthesis (Boote et al., 1996). Valentinuz and Tollenaar (2006) reported that breadth of the area per leaf profile decreases under high soil nitrogen level and high plant density. They were reported that leaf area and yield increased with higher rate of N. According to Pandey et al. (2000), maize cultivars differs in its ability to maintain Leaf Area Index (LAI), Crop Growth Rate (CGR) and above ground dry matter biomass at different levels of water deficit and N supply. Plant height, inter-node length and ear height is greater under high density and leaf area decreases with increase in plant density in maize (Modarres et al., 1998; Hassan, 2000). Plant height and yield in maize increases up to a plant density of 71900 plants ha-1 and 280 kg N ha-1, but further increase in both plant density and N rate has no significant effect on the plant height and biomass yield (Turgut, 2000). Plant density in maize affects plant architecture, alters growth and developmental patterns and influences assimilate production and partition (Casal et al., 1985). The aim of this study investigate to impacts of differential N rates and maize density at Southeast of Iran with the objective of evaluate the effect of plant densities and N dosages on maize yield and PAR absorption.
MATERIALS AND METHODS
Experiment was conducted at the University of Zabol, The experimental farm in Southeast of Iran during 2007-08. The experimental site is located at 30°54' N, 61°41' E and 483 m above sea level and it has arid type of climate. Soil texture is sandy loam, extractable phosphorus (11 ppm), exchangeable potassium (115 ppm), exchangeable nitrogen (0.05%) and alkaline (pH 7.6); climatologically data are mean of rainfall this region is 53 mm annual and mean of evaporation at annually is 5000 mm (Research Center of Zabol Agriculture). A split plot experiment was conducted in a Randomized Complete Block (RCB) design with four replications. Split plot experimental treatments were three plant densities (P1 = 60,000 plants ha-1, P2 = 80,000 plants ha-1 and P3 = 100,000 plants ha-1) applied to sub plot and four N rates (N1 = 200 kg N ha-1, N2 = 250 kg N ha-1, N3 = 300 kg N ha-1 and N4 = 350 kg N ha-1) applied to main plots. K.S.C 704, corn variety was used in the experiment. A sub-plot size of 2 mx6 m, having 4 rows, 6 m long and 50 cm apart, was used. Fertilizer N (urea) was applied at the time of sowing and two stage (6 leaf and stem elongation). A uniform basal dose of 150 kg P2O5 (super phosphate) ha-1 and 100 kg K2O (Sulphate of potassium) ha-1 was applied and mixed with soil during seedbed preparation. The plots were planted thicker and the three desired plant densities of 60,000, 80,000 and 100,000 plants ha-1 were obtained in the different experimental units by thinning two week after emergence. Ten plants in the four middle rows in each experimental unit were harvested at silking and physiological maturity. The plants were dried, weighed and then converted to yield ha-1. The fraction of PAR intercepted was calculated by taking ten readings in rapid succession above the canopy and ten readings below the canopy at the soil surface using a Ceptometer CEP (Decagon Devices, Pullman, Washington State and USA). The soil surface measurements were taken by placing the Ceptometer at right angles to the plant rows.
Statistical analysis: All obtained data was subject to statistically analyzing according to Steel and Torrie (1980) and mean values were compared with treatments by Least Significant Different (LSD) at p = 0.05 level.
RESULTS AND DISCUSSION
0Grain yield: Grain yield of maize showed positive relationship with
increase in plant density (Table 1).
The highest grain yield was obtained at P3 (3610 kg ha-1) and the lowest grain yield was obtained at P1 (2460 kg ha-1). Light interception was increased with increased plant density, under high plant density increased plant heights as well as light interception. At high density vegetative growth of maize was extended, more number of leaves per plant were produced that increased light interception at the high density (Amanullah et al., 2009), as a result more assimilates were produced by maize crop that increased plant heights as well as light interception (Amanullah et al., 2008; Tollenaar et al., 1997) which ultimately lead to higher grain yields at high than at low plant density. Toler et al. (1999) were reported 15% higher light interception and higher biomass yield at high than at low plant density of maize. Edwards et al. (2005) were suggested that increasing plant density for short season maize increased cumulative intercepted photo synthetically active radiation, which compensated for a short growing season to achieve high yield. At low plant density, the in adequate number of plants and therefore ears, that was concluded limits grain yield (Hashemi et al., 2005). Aftab et al. (2004) were reported that a linear relationship between total biomass production and intercepted PAR. High yield thus require agronomic techniques that produce both a high level of radiation interception and a high rate of conversion of intercepted PAR to grain. Similar results was obtained by Hassan (2000) and Silva et al. (1999) that observed increase in grain yields with increasing plant density.
Grain yield increased significantly with increase in N rate (Table 2). The increase in grain yield at higher N than lower N rate might be due to the increase in leaf area and plant heights at higher than at lower N rate. Hamid and Nasab (2001) and Greef et al. (1999) were reported positive correlation between N rates and dry matter yield in maize.
| Table 1: | Impact of planting density on grain yield and PAR absorption at physiological maturity of maize during 2007-08 |
| Where, P1 = 60,000 plants ha-1, P2 = 80,000 plants ha-1 and P3 = 100,000 plants ha-1. Mean values of the same category followed by different letters are significant at p≥0.05 using LSD | |
| Table 2: | Impact of N rates on PAR absorption and grain yield at physiological maturity of maize during 2007-08 |
| Where, N1 = 200 kg N ha-1, N2 = 250 kg N ha-1 , N3 = 300 kg N ha-1 and N4 = 350 kg N ha-1. Mean values of the same category followed by different letters are significant at p≥0.05 using LSD | |
Rajcan and Tollenaar (1999) reported that the difference in the dry matter accumulation in maize is attributed to post-silking N uptake and it significantly increases with increase in N rate. Mariga et al. (2000) resulted that total yield in maize considerably increased when N was applied up to tassel initiation stage.
Radiation interception was also influenced by the levels of nutrients in plants, mainly by nitrogen (Scott Green et al., 2003). Kogbe and Adediran (2003) were reported that High fertilizer input is one of the conditions required to obtain maximum yield of hybrid maize. These results agree with those reported by Mahmood et al. (2001), Nunes et al. (1996), Shaikh et al. (1994), Ali et al. (2002) and Jehan et al. (2006).
CONCLUSIONS
Present results indicated that application of nitrogenous fertilizer increased grain yield of maize. This is possible because the presence of nitrogen helps in developing leaf area as a result of the increase in the physiological growth indices. The results showed that application of nitrogenous fertilizer increased the grain yield and absorption of PAR in maize. Also, our study showed that high planting density contributed to grain yield by increasing absorption of PAR.
Application of higher rate of 350 kg N ha-1 resulted in maximum biomass yields and PAR absorption. Further research work for understanding the impacts of different planting densities, higher rate of N for high sustainable grain production in arid agro ecological conditions is also suggested. Sowing maize in 50 cm width and 20 cm between plants (100,000 plants ha-1) and application 350 kg ha-1 produced the highest grain yield and was absorbed the highest amount of PAR.
ACKNOWLEDGMENTS
The authors thank Ebrahim Mirshekar for useful comments on Agronomy Laboratory. Financial support from the Department of Agronomy, Faculty of Agriculture in Zabol University.