THE EFFECT OF TIME OF HARVEST ON LOSSES A ND QUALITY OF PRODUCTION OFRAPE, WHEAT AND BARLEY

Tolerance of winter rape, winter wheat and spring barley to delayed ha rvest was studied. The study was aimed at determination of the course of biological losses and changes in qualitative traits in the period a fter elapsing an optimum term of the ripeness, i.e, to make possible t he use of harvest machinery in longer harvest season. Many authors wer e dealing with this problem, particularly in cereals (Hunt, 1978; Vonk a, 1980; Turcek, 1980; Witney, 1988). In most of quoted studies author s coincide in the fact that the course of losses in dependence on time is of non-linear character and dependences characterizing especially biological losses for various conditions were studied. The fact that i n dependence on various moment of performance of the harvest, seeding, planting, protection, etc., biological losses and changes in the qual ity of resulting product occur, was used by some authors (Spelina et a l., 1973; Maskova et al., 1976; Witney, 1988; Oubrecht, 1991; Kochan, 1996; Kavka, Kolek, 1996; Kavka et al., 1997) to optimize the number o f machines necessary for performance of work. Hence comprehended consi deration needs, except biological losses, know total losses and change s in the quality of resulting product or the change of the market prod uction in dependence on time. That is why in the years 1994 and 1995 a t the experimental sites of the Research Station at Cerveny Ujezd, yie lds, losses and quality of production of winter rape, winter wheat and spring barley were investigated. The results indicate a significant g rowth of pre-harvest losses of rape (Fig. 1) and relatively low losses of wheat and barley (Figs 2 and 3). Qualitative traits, such as TKW, oil content, protein content, portion of prominent grain, etc., almost do not change (Figs 4 to 8 and 11 to 12). However, the risk of occurr ence of sprouted seeds and molds, mycotoxins is greater. In food wheat and malting barley is another risk of food and malting loss during ab out 10 days from the beginning of harvest. This is caused by bulk dens ity (Fig. 10) in wheat and crude protein content (Fig. 9) in barley. I n addition, gradual increase of water content of harvested production was found (Tab. III), that is in relatively drier and warmer condition s of harvest (Tabs I and II). Delayed harvest is hence very unsuitable for rape, wheat and barley from the point of view of production and e conomy.