Studies On Physiological Characters Of High-yield Summer Maize (Zea Mays L.) Population Under Limited Thermo-unit Conditions

Solar radiation and thermo-unit for maize production under winter wheat- summer maize double cropping system is limited in Hebei province. In order to understand the characters and approaches to high-yield of summer maize under limited thermo-unit conditions, a field study was conducted in Shenzhou and Xinji counties from 2005 to 2006 with 4 maize hybrids, Zhengdan-958, Xianyu-335, Xundan-20 and Denghai-3719. Growth and development, morphological and photosynthetic characters, dry matter accumulation and partitioning, grain filling, accumulation of N,P,K and their usage efficiency, and yield components were observed. The results showed as follows.Growth and development of high-yield summer maize characterized with higher plant uniformity, higher coefficient in stem diameter, lower ear height coefficient, more prop roots and resistant to lodging. The maximum leaf area index (LAI) was more than 5.6, the time with high LAI was long, and LAI maintained over 3.5 in maturity. The total Leaf area duration (LAD) was over330·10⁴.m²Â·d/hm², and percentage of the LAD from silking to maturity was 68%. From twelve-leaf stage to 30-days-after-silking, the photosynthetic rate of the main leaves gained 44.0μmolCO₂/m²Â·s .To control the proper maximum LAI and to increase the percentage of LAD after silking were the basis for high yield.Total biomass accumulation of the aerial parts and grain fit in with Logistic curve. Dry matter accumulation of leaves, stem, sheath and other organs showed a single peak curve throughout the entire-growth. Total amount of dry matter accumulation of high-yield summer maize arrived 20400kg/hm², and the percentage of biomass from silking to maturity counted about 60%. The amount of dry matter productivity averaged 200g/hm²Â·d. The transfer rate of dry matter into grains was higher from leaf than from sheath and stem. Maximum grain filling rate appeared earlier and higher grain filling rate during rapid grain filling period were needed for obtaining high yield. Increasing the amount of dry matter accumulation after silking and promoting grain filling was the basis of high yield. Maximum absorption rate of K by maize plants appeared earlier (twelve-leaf stage), then N and P. Differences of absorption for N, P and K were found between hybrids. Total amounts of N,P,K accumulated after silking was higher for high yield summer maize, especially the nitrogen. To produce per 100 kilograms of biomass or grain, maize plants needed more for N and K. Compared with other hybrids, Zhengdan-958 absorbed less N and more K to produce per 100 kilograms of biomass or grain. To chose hybrid with high efficiency of N, to increase potassium fertilizer and to add nitrogen fertilizer during grain filling period are required to obtain high yield in summer maize.The yield components of the high-yield summer maize were about 65000 ears/hm², averaged 580 grains per ear, total kernel number of 37.5·10⁶/hm², grain weight above 330g/1000 grains, harvest index above 0.5, and ratio of total grain weight to maximum LAI above 1.50 g/dm². Under limited thermo-unit conditions, keeping optimum ear numbers per hectare, increasing ear grain numbers per ear and remaining grain weight were important for high yield.