Sowing dates and densities in a function of winter wheat yield in the long-term field trial | Rokovi i gustine setve u funkciji prinosa ozime pšenice u dugotrajnom poljskom ogledu

Sowing date is one of the most important field crop management measures in the production of small grains and it practically determines the intensity of all other factors in wheat production. Among many factors which determine yield, sowing outside the optimum period, use of inappropriate seed rates and selection of cultivars insufficiently adapted to a given agro-ecological conditions, are recognized as the most common causes of low yields of winter wheat. Moreover, sowing date is economically cheapest field crop management measure and a cost-effective way to increase grain yield. However, eventual delay in sowing cannot be adequately compensated by any other field crop management measure. Extreme weather events are already a significant challenge for grain producers and are predicted to increase under numerous future climate scenarios. In these altered weather conditions, optimal sowing date with an adequate sowing density and choice of appropriate genotypes will be of great importance in order to mitigate the negative effects of climate factors on yield stability, as well as on the bread making quality of winter wheat. The aim of this research was to investigate the effects of different sowing dates, sowing densities and their interactions on yield, yield components and grain quality of different wheat cultivars. The study of interaction of sowing dates, sowing densities and cultivars of winter wheat was carried out on experimental fields of the Institute of Field and Vegetable Crops, in the 1981/82. – 2012/13. period. The experiment was set each year, on the calcareous chernozem soil, as a three factor trial (split-split-plot design), in four replications, with variants in the randomized block design. During the 32-year studied period, grain yield has varied considerably depending on weather conditions and ranged from 4.35 t ha-1 in 2003., to 8.70 t ha-1 in 2013., on average for all treatments. It was observed that the annual increase in yields during the investigated period was 10.7 kg ha-1. From the 32 years analyzed there were 5 years with high yields, 12 years with low grain yields, while the remaining 15 years could be identified as a medium yielding years. There were significant differences in temperature regimes and moisture conditions between these three types of years. Yield variation caused by the different sowing date was much lower in high yielding in comparison to low yielding years. For the entire examined period, on average of all tested cultivars and planting densities, the highest grain yields were obtained in the II sowing date (11-20. X), and were significantly higher in comparison to all other sowing dates, except the earliest (I sowing date). There were no statistically significant differences in yields between I and III sowing date, but they were significantly higher in comparison to sowing in November and December. Second sowing date had the lowest yield variation during the studied period. Sowing in November reduced yield by 11% and December sowing by 27% on average, compared to optimal (October) sowing dates. During the investigated period, average daily reduction of grain yield was 38 kg day-1. The smallest decline in yields caused by the delay in sowing was in high yielding years, followed by medium yielding, and the largest yield decline was found in low yielding years. In the optimal sowing dates (I and II), a density of 500 viable kernels m-2 proved to be optimal, while in the later sowing dates (November and December), increasing the sowing density up to 700 viable kernels m- 2, was justified. Delay in sowing from I to V sowing date caused an increase in the bread-making quality parameters such as protein content, wet gluten content, water absorption capacity, Zeleny sedimentation value, bread loaf volume and value number of bread, for both cultivars examined. On average for all sowing dates and densities, cultivar Zvezdana achieved higher values for almost all bread-making quality parameters tested in comparison to NS 40S.