Wheat-soybean rotation planting pattern is an important farming system in North China Plain. The long-term average (from 1971 to 2008) annual rainfall was 696.6 mm. In most years, rainfall does not exceeded 200 mm, but water requirement of winter wheat was about 400 to 500 mm during the winter wheat growing season. As a consequence, winter wheat yield reflects the amount of stored soil water, rainfall and water applied through irrigation. A great deal of studies showed that irrigation regime of winter wheat affected on yiled, water use efficiency (WUE) and pre-sowing soil moisture of following crop.
The results of the work on photosynthetic characteristics, yield and WUE of summer soybean (Glycine max cv. Ludou 4) under different pre-sowing soil moistures and planting patterns, as well as possible ways to improve water utilization, have been reported. The experiment was carried out from June to September in 2009 at Agronomy Experimental Station of Shandong Agricultural University (36°09'N, 117°09'E). The winter wheat experiment consisted of 3 irrigation schedules, i e, 90 mm, 135 mm, 180 mm which were used at jointing stages (April 2, 2009), heading stages (April 24, 2009) and filling stages(May 13, 2009) respectively; the amount of irrigation was 30 mm, 45 mm and 60 mm every time. The summer soybean consisted of 3 planting patterns under the same plant population density (3.09×10⁵ plant/hm²). The row width set at uniform row with 30 cm, narrow-wide row with (20+40) cm(row widths set at a narrow row of 20 cm and a wide row of 40 cm) and ridge with (20+40) cm (double lines in ridge with 20 cm spacing, and 60 cm between ridges). The results showed that pre-sowing soil moisture of summer soybean increased with irrigation amount of winter wheat increasing, and photosynthetic function and yield were also improved. Net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration, chlorophyll content index, F0, Fv, ΦPSⅡ, yield and WUE of summer soybean,for the 180 mm and 135 mm irrigation of winter wheat, were significantly higher than those of the 90 mm, but WUE of the 180 mm was significantly lower than that of the 135 mm (P < 0.05). Compare with uniform row planting pattern and narrow-wide row planting pattern, ridge planting pattern obviously increased net photosynthetic rate, transpiration rate, stomatal conductance, chlorophyll content index and chlorophyll fluorescence parameters, enhanced yields and WUE.
In all the experiments, under the amount of irrigation 135 mm and 180 mm of winter wheat, yields of the ridge planting pattern of summer soybean were significantly higher than those of other treatments. Under the ridge planting pattern, The WUE of summer soybean under the amount of irrigation 180 mm of winter wheat was 6.32 kg·hm^-2·[KG-*4]mm^-1, which lower than of the amount of irrigation 135 mm of winter wheat. Considering economic and ecological benefits. The ridge planting pattern of summer soybean was recommended under the amount of irrigation 135 mm of winter wheat, which was the optimal combination in the experiment.