Effects of irrigation and planting patterns on radiation use efficiency and yield of winter wheat in North China

The factor limiting the increase in winter wheat yield was not the deficiency of light radiation but the low radiation use efficiency (RUE). In 2004-2005 and 2005-2006, an experiment was conducted at the Agronomy Station of Shandong Agricultural University to study the effects of irrigation and different planting patterns on the photosynthetic active radiation (PAR) capture ratio, PAR utilization, and winter wheat yield. In this experiment, winter wheat was planted in four patterns as follows: uniform row planting (U; row spacing, 30 cm), “20 + 40” wide-narrow row planting (W), “20 + 40” furrow planting (F), and “20 + 40” bed planting (B), which are very popular in North China. The results showed that under different irrigation regimes, there was no significant difference (less than 15.93%) between any of the planting patterns with respect to the amount of PAR intercepted by the winter wheat canopies. However, significant differences were observed between different planting patterns with respect to the amount of PAR intercepted by plants that were 60-80 cm above the ground surface (53.35-225.16%). This result was mainly due to the changes in the vertical distributions of leaf area index (LAI). As a result, the effects of the planting patterns on RUE and the winter wheat yield were due the vertical distribution of PAR in the winter wheat canopies. During the late winter wheat growing season, irrespective of the applied irrigation, the RUE in case of F was higher than that in case of U, W, and B by 0.05-0.09, 0.04-0.08, and 0.02-0.12 g/mol, respectively, and the yield was higher by 238.39-693.46, 160.02-685.96, and 308.98-699.06 kg/ha, respectively. Only under the fully irrigated conditions, the RUE and winter wheat yield significantly (LSD; P < 0.05) increased in case of B. This experiment showed that in North China, where the water shortage is the highest, application of planting pattern B should be restricted. Instead, F should be used in combination with deficit irrigation to increase the RUE and grain yield of winter wheat.