Sarhad J. Agric. Vol.26, No.2, 2010 EFFECT OF SEED RATES ON THE AGRO-PHYSIOLOGICAL TRAITS OF WHEAT IQTIDAR HUSSAIN, MUHAMMAD AYYAZ KHAN and HAYATULLAH KHAN Department of Agronomy, Faculty of Agriculture, Gomal University, Dera Ismail Khan – Pakistan. Email: aqdusdik@yahoo.com ABSTRACT The effect of different seed rates on agro- physiological traits of wheat varieties was investigated at agronomic research area, Faculty of Agriculture, Gomal University D.I.Khan. Six wheat varieties viz. Inqilab- 91, Bakhtawar-92, Punjab-96, Dera-98, Daman-98 and Raj. were tested using varying seed rates of 50, 100, 150 and 200 kg seed ha -1 under a split plot arrangement during 2000-01. The effect of seed rates was significant on most of agro-physiological traits of tested varieties. Tillers m -2 , fresh weight, crop growth rate, net assimilation rate, photosynthetic efficiency and protein content were high at higher seed rate of 200 kg ha -1 . Among wheat varieties, Inqilab-91 produced maximum fresh weight, net assimilation rate, photosynthetic efficiency and grain yield. Daman-98 produced more dry weight (9.15 t ha -1 ) and protein content (11.40%). Tillers m -2 (350.4) and maximum crop growth (15.04 g d m -2 ) rate was recorded for punjab-96. In interaction, maximum grain yield 6.50 t ha -1 ) was produced by Daman-98 with seed rate of 200 kg ha -1 . Daman-98, Inqilab- 91 and Bakhtawar-92 produced maximum grain yield at higher seed rate . While Raj produced maximum grain yield of 5.0 t ha -1 at 50 kg seed ha -1 . Dera-98 gave maximum grain yield of 5.97 t ha -1 at 100 kg seed ha -1 and Punjab-96 produced maximum grain yield of 5.41 t ha -1 at seed rate of 150 kg ha -1 . Key Words: Wheat, varieties, agro-physiological traits, seed rates, Pakistan Citation: Iqtidar, H., M.A. Khan and H. Khan. 2010. Effect of seed rates on the agro-physiological rtaits of wheat. Sarhad J. Agric. 26(2): 169-176. INTRODUCTION Wheat (Triticum aestivum L.) is the most important among all cereals used as a food grain in the world. It ranks first in the world cereal production and is a staple food of about one third of the world’s population. In Pakistan, it contributes 12.1% to the value added in agriculture and 2.9% GDP (Anonymous, 2001). To feed the ever-increasing population in the country, the need for more wheat will be continued. There are high possibilities to increase wheat yield in Pakistan through developing new high yielding varieties and by adoption of proper package of technology (Arian et al. 2002; Mahboob et al. 2005). Concerns are being expressed that yield plateau have been reached in major crop species including wheat. If further increases in food production per hectare are to be realized, improved management systems and cultivars, which respond to our cultural practices, must be developed. The continuous supply of new germplasm material as donor of various genes of agronomic importance is a vital prerequisite for further improvement of wheat cultivars (Masood et al. 2005). Plant density is one of the major factors determining the ability of the crop to capture resources; it is of particular importance that it is being under fairly close control by the farmers in most wheat-producing systems. There has been interest in defining the relationships between density and crop yield quantitatively in order to establish optimum populations and maximum attainable yields under various situations. As a result, the effect of density on wheat plant size and crop productivity has received attention (Harper, 1977). There is no uniform recommendation by agronomists regarding the seed rate for unit area, for example, Ciha (1993) reported that higher yield can be obtained by sowing 75 kg seed ha- 1 . While Singh and Singh (1984), Khan (1993) and Shah (1994) recommended 100 kg seed rate ha -1 for obtaining higher grain yield of wheat. A number of factors can influence the rate of photosynthesis and respiration in plants, and the term net assimilation rate (NAR) commonly is used as a measure of the rate of photosynthesis minus respiration losses. Factors that influence net assimilation rate are temperature, light, carbon dioxide, water, leaf age, mineral, nutrients, chlorophyll content and genotype (Stoskopf, 1981). The importance of the duration of photosynthesis to grain yield was reported by Daynard et al. (1971). In wheat, Spiertz et al. (1971) found that 61 to 83% of the variation in grain yield could be predicted from the duration of photosynthesis of the flag leaf and sheath. The flag leaf is the final uppermost leaf to develop on cereal plants and is formed just prior to fertilization. Photosynthetic activity of a leaf canopy was found to reach a maximum after anthesis and declined rapidly thereafter. Stoskopf (1981) reported that all yield factors depend on available food energy to produce grain yield. Such components draw on a fixed pool of food energy, and if yield is to be increased then photosynthesis