Description of experiment location and planting operation The studies were carried out at the Agricultural Research Sta- tion at Dirab, (24460N and 25340E) 40 km southwest of Riyadh, Saudi Arabia. Soil samples were collected from the 0–20 cm, 20–40 cm and 40–60 cm depth and analyzed for chemical and physical characteristics at the Ministry of Agriculture and Water resources laboratory located in Riyadh, Saudi Arabia. The soil is classi?ed as sandy and characterized by pH
(H2O) 7.62, total N: 0.00 g kg1, available P: 9.33 mg kg1 (Mehlich method), exchangeable K: 186 cmol kg1. Other related properties of top soil are as fol- lows: water holding capacity is 0.18 v/v% and wilting point is 0.09%. During the experiment period, rainfall was zero, while minimum temperature ranged from 25.87 C in July to 12.71 C in November. Maximum temperature also ranged from 43.8 C in July to 26.08 C in November. Six promising inbreds were sown at different dates in July 2009 by planting medium maturing genotypes before early maturing genotypes at ?fteen days interval to achieve proper synchronization of ?owering between parents. Detail of the inbreds is given in Table 1. Cross pollination was done using all possible combinations without reciprocals to give a total of 15 crosses following the procedure outlined by Russell and Hallauer (1980). The set of ?fteen F1’s and their six par- ents were grown in July 2010. Land preparation was done by harrowing, ploughing and disking the soil at appropriate inter- vals. The sowing was done by putting two seeds in a hole and later thinned to one plant per hill to maintain a row-to-row and plant to plant distances of 75 and 20 cm respectively. A compound fertilizer in form of NPK 18:18:0 was applied before planting. Weeding was carried out manually 3 times during the growing period.