Effect of different planting dates on growth attributes, grain yield and protein content of three wheat cultivars in Kerman

  Winter wheat is the most important staple food crops in the country, with a total farming area of nearly 6.33 million ha and a production exceeding 14 million ton in 2015. Wheat is a thermo-sensitive crop, and change in air temperature may alter the length of its growing period and subsequently grain yield (Chattaraj et al., 2014). Wheat reproductive period duration is determined by a combination of planting date and variety (Wang et al., 2015). Extreme weather events, such as spring heat stress, can have substantial impacts on crop growth and grain yield. Therefore, improving tolerance to high temperature stresses during flowering and grain filling is great significance to wheat production. The present study was performed to evaluate the effect of planting date and variety management strategies on winter wheat production in Kerman.
Material and In order to investigate the response of three common cultivars of wheat to various planting dates in Kerman region, the two-factor experiment was set up in a Split-plot arranged in a randomized complete block design with three replications to assess the growth, yield and morphological traits of three different varieties of irrigated wheat with different maturity length at different planting dates (20 October, 5 November and 20 November). These varieties included early maturing (Mihan), medium maturity (Arg) and late maturity (Omid). According to the local soil test recommendations, basal doses of 220 kg ha-1 Urea and 100 kg ha-1 Triple Super Phosphate were incorporated into the soil. As soon as the seeds were sown, irrigation continued every 10 days. Experimental field soil in the 0-30 cm depth was silty loam with pH 7.2, containing total N (0.071 %), total P (21 ppm), and total K (348 ppm) with an EC of 2.69 ds m-1. Combined analysis of variance showed that planting date had a significant effect on plant height, number of grain per spike, length of growth period, grain and biological yield. 1000 grain weight, leaf area index, harvest index and grain protein contents were not affected by planting date. The highest plant height (112 cm) and length of growth period (206 days) were obtained at the first planting date (20 October). The cultivation of wheat on 15th November produced the highest number of grain per spike (32.71), biological yield (14.45 t ha-1) and grain (5.16 t ha-1). The effect of variety on all the traits except 1000-grain weight was significant. Omid cultivar had the highest plant height (134 cm) and growth period (209 days). The others of the studied traits were significantly higher in Mihan variety than Arg and Omid varieties. For example, grain yield in the Mihan, Arg and Omid was 6.33, 4.7 and 4.63 t ha-1, respectively. The interaction of planting date and variety showed that the highest grain yield for Omid (4.99 t ha-1) was produced in the first planting date (20 October) and in Arg (4.3 t ha-1) and Omid (6.27 t ha-1) was obtained to the second planting date (5 November). The lowest grain yield of all the three varieties was assigned to the third planting date (20 November). The grain protein contents varied from 10.11 to 11.61%, which the highest value was gained in Omid variety, cultivated on 20 November. The period centered on anthesis constituting the most sensitive stage of wheat to high temperature (Eyshi Rezaei et al., 2015). The observed sensitivity of wheat yields to high temperatures has been attributed to accelerated development, reduced photosynthesis and the direct impacts on reproductive processe). The negative correlation between high temperature around reproductive stage and reduced grain numbers, with significant negative impacts on grain yield was previously illustrated. A threshold temperature of 31° C for wheat is generally accepted as an upper limit to temperature near flowering without reductions in grain yield (Porter and Gawith, 1999). Planting the short maturity variety allows the wheat to escape the hot weather and led to non-coincidence of the reproductive stage with high temperature especially in future climate conditions. In general, the best planting date for Omid variety is October 30, and for Arg and Mihan varieties is proposed the 5 November.