Study On Seeding Emergence Characteristics Of Maize(Zea Mays L.) Under Different Sowing Depths

As one of the important maize producing areas in China, southwest hilly area plays a important part in the national maize production. Seasonal drought is a primary limiting factor for maize production in this area, especially spring drought, it has the highest frequency and threats germination and emergence of maize. The full stand and healthy seedling are basic guarantees to obtain high-yield, deep-sowing has advantages to avoid less soil surface moisture and ensur that seed germination has enough water, but in the practical production, due to differences in soil type, top soil ability in maize varieties and other conditions, deep-sowing often leads to no or less emergence and weak seedling quality. Therefore, in conditions of the purple soil hilly area at Sichuan, the study on emergence characteristics under different sowing depths in maize varieties will be the important precondition for further selection and identification to deep-sowing tolerance in maize varieties.In this study, we uesed eight maize varieties with larger planting area in hilly area of Sichuan:Zhongdan808, Chengdan30, Chuandan418, Dongdan60, Changyu13, Chuandan14, Zhenghong311and Longdan No.9, analysed the changes in seedlings morphological, growth mass and endogenous hormone content under different sowing depths, drawed the following main conclusions:1. Under different sowing depth treatments, the soil water content showed a increasing trend with increasing sowing depth, the differences of increasing extent was greater in3～9cm sowing depth treatments and smaller in12～21cm sowing depth treatments; the diurnal variation extent of soil temperature showed a decreasing trend with increasing sowing depth, the thermal insulation effect of6cm and9cm were not obvious,12～21cm were obvious, there were less difference in highest soil temperature.2. Under different sowing depth treatments, the germination rates of eight maize varieties showed a decreasing trend with increasing sowing depth, there were some differences among different varieties, Zhongdan808, Chengdan30and Chuandan418had smaller decreasing extent and higher seeding emergence relatively; the emergence time of eight maize varieties showed a delayed trend with increasing sowing depth, all varieties were delayed on average of2～3d under6cm sowing depth treatment, all varieties seeding emergence time were delayed on average of4～8d under9cm sowing depth treatment, there were no significant differences among different varieties.3. Under3～9cm sowing depth treatments, seedlings length, coleoptile lengh, mesocotyl length, seedling fresh weight and dry weight, mesocotyl fresh weight and dry weight, and root fresh weight of maize showed a increasing trend with increasing sowing depth, seedling uniformity, mesocotyl diameter, root length, ratio of root and shoot at fresh weight and dry weight showed a decreasing trend with increasing sowing depth, while coleoptile diameter, total root number and root dry weight had been effected slightly by sowing depth, there were some differences among different varieties, Zhongdan808, Chengdan30and Chuandan418had better performence comprehensively.4. Under3～9cm sowing depth treatments, there were some differences in both of the correlation coefficient and association degree between seedling qualitative traits and seedling emergence rate of maize; Under deep sowing depth, the correlation coefficient and association degree between mesocotyl length and seeding emergence rate were highest, so we could uesed mesocotyl length as the important identification indexs for deep-sowing tolerance in maize.5. The different varieties had very significant differences in emergence potentiality traits; There were some differences in both of the correlation coefficient and association degree between emergence potentiality traits and seedling emergence rate under3～9cm sowing depth treatments in maize; The correlation coefficient and association degree between the total potential length of coleoptile and mesocotyl and seeding emergence rate under deep sowing depth were highest, so we could uesed the total potential length of coleoptile and mesocotyl as the important identification indexs for deep-sowing tolerance in maize.6. Under3～9cm sowing depth treatments, GA3and ZR content increased obviously in leaves of maize, IAA/ABA increased and ZR/ABA decreased obviously in young stem, IAA/ABA and GA3/ABA increased obviously in mesocotyl, all endogenous hormones content had less change in root; The ABA contents of all seedling organ in maize decreased in some extent, therefore, increasing sowing depth had some compensation effects on seedling growth of maize.