Research on technology of grain production under double-cropping system in Yantai City

Yantai (a city in Shandong Province) is a strong base for winter wheat-maize double-copping system. A previous double- copping system experiment involving single-stem late wheat intercropped with late-maturing maize in Longkou (a county of Yantai City) yielded 22 770 kg·hm^-2. Other studies have reported grain yields excess of 22 500 kg·hm^-2 in North China. For various reasons, however, replicating these experiments at field scales has not been feasible. As one of the first institutions to develop super- high-yield experiments, the Grain and Food Safety Research Center of China Agricultural University was founded in July 2004 in Yantai City, Shandong Province, at where we conducted a 3-year experiment on high-yield technology system of double-cropping system. Based on weather analysis in Longkou and Laizhou Counties of Yantai City, where super-high-yield experiments were first conducted, this paper put forward a new research direction that makes rational use of the abundant light, heat and species resources in Yantai for high-yield wheat-maize double copping system. The strategy delayed the sowing time of wheat to get the effective temperature (≥16 oC) for maize to fully exploit yield potential of longer growth period maize varieties. Two modes of double-cropping system cultivation techniques with suitable improved varieties were designed and selected. Based on the design, Longkou was best fitted for a double-copping system of mid-late wheat intercropped with mid-late maturing maize with Oct. 10 → Oct. 10 crop-rotation periods. Laizhou, on the other hand, was best fitted for double-copping system of single-stem late wheat variety mixed with mid-late maturing maize with Oct. 15 → Oct. 15 crop-rotation periods. Furthermore, the corresponding suitable varieties were incorporated into the experiments. The results of the double-copping system experiments were as follows: Longkou was suitable for the mid-late wheat “Liangxing 99” intercropped the mid-late maturing maize “Jinhai No. 5” of double-copping system with Oct. 10 → Oct. 10 crop-rotation period. Laizhou was suitable for directly sowed single-stem late wheat “Liangxing 99” mixed with the mid-late maturing maize “Jinhai 607” of double copping with Oct. 15 → Oct. 15 crop-rotation period. The results of three-year high-yield experiments in Laizhou and Longkou showed that yields were above 21 000 kg·hm^-2 per year. Yields for the last year reached the expected target of 22 500 kg·hm^-2. Yields for the area of 0.074 hm² reached 24 792.45 kg·hm^-2 for the two seasons. The study showed that wheat-maize double-cropping system technology that made full use of light, heat and variety resources was more rational for Yantai, which brought local potential productivity to full realization.