257 Journal of Oilseed Brassica, 6 (2) July., 2015 Effect of sowing direction and crop geometry on water use efficiency and productivity of Indian mustard (Brassica juncea. L.) in semi arid region of India Somnath Jha 1 *, V K Sehgal 2 and Y V Subba Rao 2 1 Deputy Magistrate & Deputy Collector, Uttar Dinajpur District Collectorate (Government of West Bengal) Karnajora, Uttar Dinajpur - 733130, India 2 Division of Agricultural Physics, Indian Agricultural Research Institute (I.A.R.I), New Delhi-110012, India Corresponding author: somnath.jha@gmail.com (Received: 15 October 2014; Revised: 15 June 2015; Accepted: 20 June 2015) Abstract Indian mustard [Brassica juncea (L.) Czern & Coss.] is an important oilseed crop for the rainfed, semi-arid region of north-western plains of India. The best direction of sowing with respect to yield is still not clear. Therefore, two Indian mustard varieties differing in their phenotypes (erect and spreading type) were grown in two sowing directions [North-South (NS) and East-West (EW)] along with broadcast to study the effect of direction of sowing, and planting geometry on the actual evapotranspiration (AET), water use efficiency (WUE), biomass production, and yield. Accumulated AET was studied to be higher in the EW direction than in NS sown plots. Direction wise NS sown plots showed higher WUE, and better AET-yield production function (higher coefficient of determination) than the EW sown plots. EW sown plots produced the highest seed yield followed by broadcast sown, and NS sown plots, and proved to be the best in terms of WUE, biomass production and seed yield. Keywords: Crop phenotype, direction of sowing, planting geometry, water use efficiency Journal of Oilseed Brassica, 6 (2): 257-264, July 2015 Introduction Indian mustard is an important oilseed crop of northern and north western part of India. It is grown as rainfed crop in the north Indian plains. There are many opinions about the best direction of sowing of Indian mustard with regard to the high seed yield. No consensus has been reached yet with definite scientific exploration. Jha et al. (2012) has studied the effect of direction of sowing, and crop phenotype on light interception efficiency, and seed yield of Indian mustard. On the contrary, water use efficiency (WUE) is more important for oilseed productivity for a water limited or rainfed region. Therefore, this present study has been done as a complementary study of the study of Jha et al (2012). The present study addressed this important issue of the effect of sowing direction on Indian mustard seed yield with respect to water use efficiency (WUE), and actual evapotranspiration (AET). WUE and AET addressed water as the major limiting factor of this rainfed zone. It is well established fact that when water supply is limiting there is a linear relationship between crop yield or biomass and the amount of water used for evaporanspiration (DeWitt, 1958; Viets, 1962). The relationship between yield and estimated evapotranspiration for well watered soybean crop was studied by Purcell et al (2006) and they reported that yield is not linearly related to seasonal transpiration over entire range of evapotranspiration values but instead reaches an asymptote at high values. The direction of sowing and the crop phenotype affect the yield of Indian mustard crop. The changes in biomass production of Indian mustard in different directions of sowing are due to the changes of actual evapotranspiration (AET), water use efficiency (WUE), and radiation interception differently in different direction of sowing. Jha et al. (2012) studied the impact of sowing direction of the Indian mustard on the