Abstract
Four experiments were conducted over seasons at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh from November 2009 to April 2011 to investigate the growth and yield response of wheat varieties to nitrogen, plant density and sowing date. The first experiment consisted of three varieties of wheat viz. Prodip, Bijoy and Sufi, and six sowing dates viz. 15 November, 22 November, 29 November, 06 December, 13 December and 20 December. The variety and sowing date showed significant influence on yield components and yield. The highest growth parameters in terms of production of plant height, number of tillers, LAI and total dry matter were observed in the variety Prodip sown on 15 November. Due to the superior growth parameters, the variety Prodip with the same sowing date produced the highest grain yield (5.14 t ha-1) and straw yield (6.02't ha1). The results of the study also revealed that grain yield of wheat declined gradually irrespective of variety due to delayed sowing from November 15. The second experiment included three sowing dates viz. 30 November, 15 December and 30 December, and three levels of nitrogen viz. 50, 100 and 200 kg N ha-1 with a view to improving grain yield of wheat under late sown condition by adding extra N. However, the results of the study evidenced that the superior growth parameters and eventually the highest grain and straw yields of wheat were obtained from the crop when sown on 30 November and provided with 200 kg N ha-1. The third experiment explored the possibility of minimizing grain yield reduction of wheat by manipulating plant spacings (15 cm, 20 cm and 30 cm) under various sowing dates (15 November, 30 November and 15 December). From the study it was also revealed that the crop performed the best with the combination of 15 November sowing and 20 cm row spacing and produced the highest grain yield (4.76 t ha-1) and straw yield (5.23 t ha-1). By taking into account the results of these three experiments, the fourth experiment of the study was designed to evaluate the growth and yield performance of the best variety Prodip under various sowing dates (15 November, 30 November and 15 December), levels of N (100 kg ha-1 and 200 kg ha-1) and row spacings (15 cm, 20 cm and 25 cm). The highest performance of the crop in terms of growth parameters such as plant height, number of tillers hill-1, LAI and dry matter production was found when the crop was sown on 15 November with 20 cm row spacing and given 200 kg N ha-1. The superior growth performance in this treatment was reflected in terms of yield parameters and yield where the highest grain yield of 5.84 t ha-1 and straw yield of 6.12 t ha-1 were obtained. However, the variety Prodip also gave moderate grain yield (4.65 t ha-1) under late sown (15 December) condition with 200 kg N ha-1 and 20 cm row spacing. Therefore, the study reports that grain yield reduction of wheat due to late sowing condition may substantially be minimized by adopting the right variety and manipulating management practices such as row spacing and level of nitrogen.