Effects of sowing date and seeding density on growth, yield and water use efficiency of ‘Xiaoyan 60’ wheat under rainfed condition

Using drought resistant and high-yielding crop varieties is critical for high and stable crop productivity under rainfed farming condition. In this study, an experiment was conducted at Nanpi Eco-Agricultural Experimental Station of Chinese Academy of Sciences (116°40′E, 38°00′N) in 2014–2015 to investigate the performance of ‘Xiaoyan 60’ wheat cultivar under the rainfed condition. The objective of the study was to test the adaptability of ‘Xiaoyan 60’ wheat cultivar to late sowing and yield loss compensation by increased seeding rate. Treatments included two factors, sowing date and seeding density. Six sowing dates were set, which were from the 15th of October to the 14th of November with six days interval, and denoted as T1, T2, T3, T4, T5 and T6, respectively. Then there were two treatments of seeding densities — constant seeding rate (B1) and increased seeding rates with delayed sowing date (B2). In B1, sowing density was 300 kg·hm^-2 for all sowing dates, whereas in B2, it started at 300 kg·hm^-2 and progressively increased at 7.5 kg·hm^-2·day1 with delayed sowing date. Thus the sowing densities at sowing dates in B2 treatments were 300 kg·hm^-2 for T1, 345 kg·hm^-2 for T2, 390 kg·hm^-2 for T3, 435 kg·hm^-2 for T4, 480 kg·hm^-2 for T5 and 525 kg·hm^-2 for T6. The population properties, growth, yield and water use characteristics were investigated under different treatments. The results showed that the plant population traits, yield and water use efficiency varied with sowing date and seeding density. The growth period shortened with delayed sowing date, the duration for all the growth stages was also shortened. In contrast, seeding rate had no effect on growth period, but positively influenced the number of seedlings, number of spikes and dry biomass amount. Also plant height was not affected by seeding density. Delayed sowing gradually decreased the rate of seedling emergence, number of spikes per plant, plant height and dry biomass. Similarly, grain yield decreased with delayed sowing. However, the grain yield reached 6 600 kg·hm^-2 level through increase seeding density to compensate for delayed sowing. There was no significant difference among the first four sowing dates (from T1 to T4) for grain-yield-based water use efficiency, which was above 29 kg·hm^-2·mm^-1. Because ‘Xiaoyan 60’ wheat cultivar was strongly adaptable to late sowing, it was recommended for cultivation under the rainfed farming conditions. Yield loss due to delayed sowing was compensated for by increasing seeding rate, which ensured optimum plant population. The correlation between seeding density (y) and delayed days (x) of sowing could be decribed by the regression equation y = 0.368 2x² + 1.193 9x+316.7 (R² = 0.98).