Abstract:

The wheat-maize double cropping system limits the heat resources of maize ripening and dewatering, which is the key factor to restrict the development of mechanical grain harvesting in the Yellow-Huai-Hai Rivers Plain. In this paper, methods of the optimum cultivar selection and harvesting time forecast were established to provide guidance for the promotion of mechanical grain harvesting in the double cropping system of the Yellow-Huai-Hai Rivers Plain. Twenty-seven main planting cultivars were selected and divided into four types by using the two-way average method. This method based on two parameters including the accumulated temperature from pollination to physiological maturity and the grain moisture content at physiological maturity. These four types were the later maturing and higher moisture content (I), the earlier maturing and higher moisture content (II), the earlier maturing and lower moisture content (III) and the later maturing and lower moisture content (IV). When grain moisture content reduced to 28% and 25% (suitable for mechanical grain harvesting) the cultivars’ active accumulated temperatures were simulated based on measurements of vegetative growth stage and dynamic change of grain moisture. According to the accumulated temperature and the historical meteorological data, the suitable days for mechanical grain harvesting of different cultivar types were estimated by using the geostatistical analysis method based on the starting points of normal sowing dates in the Yellow-Huai-Hai Rivers Plain, thus establishing the prediction method of optimum dates for mechanical grain harvesting. The accumulated temperatures from sowing to the time reaching grain moisture of 28% and 25% were 2982°C d and 3118°C d (I), 2770°C d and 2873°C d (II), 2729°C d and 2845°C d (III), and 2860°C d and 2980°C d (IV), respectively. The time for the type III cultivar with 28% and 25% moisture content respectively was two to three days and about two days earlier than that for the type II cultivar, seven to nine days and seven to ten days earlier than that for the IV type cultivar, and thirteen to seventeen days and sixteen to seventeen days earlier than that for the type I cultivar. All types of cultivar needed six to eight days to reduce grain moisture from 28% to 25%. Under the current maize cropping pattern and the sowing date of following wheat, all maize cultivars could be planted for mechanical grain harvesting in southern Henan and northern Anhui provinces in the southern Yellow-Huai-Hai Rivers Plain, while no cultivars could be used in the northern Yellow-Huai-Hai Rivers Plain, Guanzhong Area, and Shandong Peninsula where the mechanical grain harvesting of summer maize should be realized by selecting cultivar with the shorter maturing date and the rapid dehydration characteristic. In this study, the method to predict the dynamic change of grain moisture content and the optimum time of mechanical grain harvesting was established by the accumulated temperature. This method provides a feasible technical means for rationally distributing the grain harvesting cultivars and determining the suitable harvesting time.

Key words: maize, grain moisture content, dehydration types, grain harvesting time, spatial distribution