4. Discussion
4.1. Rainfall, spring wheat and P budget
Rainfall and its distribution affect growth and grain yield of spring wheat in semi-arid areas (Patil et al., 2010). In the present study, rainfall during the first three months in the 2009 growing season was lower than that in 2010. Thereafter, rainfall was
higher in 2009 than in 2010. The different rainfall patterns had more impact on straw biomass than on grain yield, which resulted in different harvest indices between the two growing seasons (>40% in the same treatment). Gangopadhyaya and Sarker (1965) suggested
that about 75% of the total variation in yield is accounted for by rainfall distribution, and any additional rainfall above average during the month prior to sowing and germination is, in general, beneficial to the crop; but detrimental during tillering. Whilst the results in this study support their conclusion, further research is needed.