Journal of Natural Sciences Research www.iiste.org ISSN 2224-3186 (Paper) ISSN 2225-0921 (Online) Vol.4, No.7, 2014 27 Variation in Crop Co-Efficient of Maize Varieties under Irrigated Condition ZainUlAbideen Department of Water Management, Faculty of Crop Production Sciences, The University of Agriculture Peshawar-Pakistan Corresponding E-mail: zainulabideen@aup.edu.pk Abstract A field study was conducted on clay loam soil at the research farm of The University of Agriculture Peshawar during Kharif 2012 to determine the crop co-efficient of maize using two traditional (V 1 =Azam and V 2 =Jalal) and two hybrid (V 3 =3025W and V 4 =30K08) varieties having four replicates. Soil moisture was determined by gravimetric method, actual evapotranspiration (ETa) was worked out by field water balance taking into account soil moisture, rainfall, and irrigation water applied. The Potential evapotranspiration (ETo) was estimated by Pan Evaporation method. Crop coefficient (Kc) was determined by dividing ETa over ETo for all growth stages. ETa of traditional maize variety V 1 was found lowest and highest for hybrid maize variety V 4 . Comparison of seasonal ETa of selected maize varieties showed that V 2 , V 3 and V 4 had 3, 24 and 34 % higher values compared to V 1 . ETa of V 1 varied between 2.7 to 4.8 mm d -1 , for V 2 between 2.6 to 5.2 mm d -1 , for V 3 between 3.3 to 6.2 mm d -1 and for V 4 between 3.4 to 6.5 mm d -1 . The seasonal ETa of selected varieties V 1 , V 2 , V 3 and V 4 was found 411, 422, 512 and 550 mm, respectively. Results showed that ETa of hybrid varieties was higher as compared to traditional varieties. Kc values of variety V 1 ranged from 0.38 to 0.87, for V 2 it ranged from 0.38 to 0.91, for V 3 ranged from 0.43 to 1.13 and for V 4 ranged from 0.47 to 1.19. It was concluded that FAO reported Kc values of a crop are generalized one for a wide range of climate therefore,Kc value of each crop variety should be investigated and used. Keywords:Crop coefficient, Actual crop co-efficient, Reference crop co-efficient and Crop water requirement. INTRODUCTION Maize being the highest yielding cereal crop in the world is of significant importance for countries like Pakistan. Maize has its origin inasemi-aridand isnot a dependable crop for growing under dry land situation, withlimited or variable rainfall (Arnon, 1972). In Pakistan, it is planted on about 43% cropped area with the production of 461,000 tons and average grain yield of 3671 kg ha -1 and 37% in Khyber Pakhtunkhwa, produce 101,515 tons and average grain yield of 2984 kg ha -1 (Govt. of Pakistan, 2010). It is normally cultivated under smallholder continuation farming systems, both under rainfed and irrigated conditions in the major and minor seasons that keep up a correspondence to the Monsoons. For maximum production a medium matured maize crop requires between 500 to 800 mm of water depending on environment (FAO, 2012).The effect of limited water on maize grain yield is significant and cautious control of frequency and depth of irrigation is required to optimize yields under circumstances of water scarcity (FAO, 2000).However, crop growth and seed yields are generally lower in the drier seasons due to low water availability to crop need, as a result crop goes under moisture stress condition whichis the significant cause for yield loss in maize after low soil fertility (Edmeades et al, 1992). Maize crop is a C 4 plant, which is more capable to use CO 2 , solar radiation, water and N in photosynthesis as compared to C 3 crops. Crop water productivity (CWP) of maize is about twice than C 3 crops grown at the similar places. Its transpiration ratio (molecules of water lost per molecule of CO 2 fixed) is 388, corresponding to 0.0026 in CWP (Jensen, 1973). Different maize cultivars have varying water requirement and crop water use efficiencies (Asare et al, 2011). The yields and crop water productivity are different for different maize hybrids. Also irrigation water requirement differ statistically among all the hybrids (Maria, 2009). To a careful estimate, only low water availability to crop demand results 50% or more declines in average yields internationally (Wang et al,2003). Maize has a high water and nutrient demand with the flowering stage being the most sensitive to water stress during which grain yield may be decreased by declining grain number and kernel weight (Pandey et al, 2000). For normal growth and development of maize, its maximumand even yields and high class, it is essential to keep optimal soil moisture during the growing period. Only optimal situation allow the plants to use water as their needs. Objectives To find crop coefficient for various growth stages of selected maize varieties; To find crop water requirement of selected maize varieties under irrigated condition in Peshawar valley.