Effects Of Sowing Depth On Grain Yield And Physiological Characteristics Of Summer Maize

This study was conducted from 2012 to 2014 in experimental farm of Shandong Agricultural University and State Key Laboratory of Crop Biology. Two summer maize hybrids, Zhengdan958(ZD958) and Xianyu335(XY335), were used as experimental materials. 4 sowing depths(3, 5, 7 and 9 cm) and uneven sowing depth(U) were designed under sand culture and field experiments to investigate the effects of sowing depth on growth and development and yield formation of summer maize to provide theoretical references for improving sowing quality of summer maize. Main results were as follows: 1 Effects of sowing depth on grain yield and yield components of summer maizeSowing depth had significant effects on grain yield of summer maize. Both uneven and too deep sowing depth reduced canopy density after emergence, then reducing harvested ear per unit area and grain yield. Grain yield of ZD958 at 9 cm and uneven sowing depth reduced by 8.3% and 3.8%, compared to the sowing depth of 3 cm; While reduced by 7.6% and 2.9%, compared to the sowing depth of 5 cm. Grain yield of XY335 at 9 cm and uneven sowing depth reduced by 7.0% and 6.1%, compared to the sowing depth of 5 cm. In addition, sowing depth also affected ear traits of summer maize. Sown too deeply, ear length decreased, bald tip length increased, thus influencing yield components and grain yield. 2 Effects of sowing depth on biological characteristics of summer maize 2.1 Seedling traitsAs sowing depth increased, seedling emergence rate gradually decreased and seedling emergence time gradually lengthened. Compared to the sowing depth of 3 cm, seedling emergence rate of ZD958 and XY335 in the sowing depth of 9 cm reduced by 9.4% and 11.8%, respectively, seedling emergence duration of ZD958 and XY335 in the sowing depth of 9 cm prolonged 1.5 d. With the increasing of sowing depth, seedling length and uniformity decreased significantly, mesocotyl length increased significantly, coleoptile length was not significant difference; primary radicle length gradually decreased, total length of secondary radicle gradually increased, so total root length was not significant difference; total dry mass of seedling and mesocotyl increased significantly, total root dry mass was not significant difference. As sowing depth increased, soluble sugar content in each part of seedling increased and the amount of nutritional consumption of germinating seeds increased, seedling root growth rate increased, but root activity reduced. As sowing depth increased, harvested ears per unit area were reduced by decreased seedling emergence rate and seedling vigor, thus influencing yield formation. 2.2 Plant traitsSown too deeply, stalk basal internode length increased and rind penetrometer resistance reduced(RPR) significantly. RPR of ZD958 and XY335 at the sowing depth of 9 cm reduced by 7.8% and 9.9%, compared to the sowing depth of 3 cm. The number and density of vascular bundle also decreased significantly. Vascular bundle density of ZD958 and XY335 at the sowing depth of 9 cm reduced by 18.7% and 13.5%, compared to the sowing depth of 3 cm, thus decreasing lodging resistance. In addition, within a certain range, increasing sowing depth could promote nodal root development and improve lodging resistance. 3 Effects of sowing depth on physiological characteristics of summer maize 3.1 Dry matter accumulation and nutrient uptakeToo deep sowing depth reduced individual dry matter accumulation of summer maize significantly. Individual dry matter accumulation of ZD958 and XY335 at the sowing depth of 9 cm reduced by 8.9% and 13.8%, compared to the sowing depth of 3 cm; While reduced by 11.7% and 15.4%, compared to the sowing depth of 5 cm. Sown too deeply, dry matter allocation proportions of stalk and leaf increased significantly, while the dry matter allocation proportions of grain and cob decreased. Too deep sowing depth reduced N, P and K accumulation amounts of summer maize significantly. N, P and K accumulation amounts of ZD958 and XY335 at the sowing depth of 9 cm reduced by 16.3%, 12.2%, 7.7% and 13.7%, 24.1%, 10.4%, compared to the sowing depth of 5 cm. Sown too deeply, nutrient allocation proportions of stalk and leaf increased significantly, while the dry matter allocation proportions of grain decreased. 3.2 Photosynthetic characteristicsBoth uneven and too deep sowing depth reduced uniformity of plant traits(plant height and ear height) and ear length significantly, then affecting yield formation. Sown too deeply, canopy density decreased and light transmission of canopy increased; But leaf area index(LAI), SPAD value, specific leaf weight(SLW), net photosynthetic rate(Pn) and dry matter accumulation per plant were lower, finally reducing yield of summer maize. 3.3 Grain filling characteristicsSown too deeply, grain volume and fresh weight reduced in the whole grain filling period, grain moisture content decreased quickly and grain filling parameters reduced significantly. Days of maximum grain filling(Tmax) and active grain filling period(P) decreased significantly. Weight of maximum grain filling rate(Wmax) and maximum grain filling(Gmax) of ZD958 and XY335 at the sowing depth of 9 cm reduced by 5.9%, 5.2% and 5.0%, 2.5%, compared to the sowing depth of 3 cm.