Regulating Maize(Zea Mays L.)Root Distribution And Improving Nutrient Acquisition By Optimal Depth Of Nitrogen Fertilizer

The maize variety Zhengdan 958(compact type maize) was chosen as the experimental material. Under field and pillar condition experimental variables were four different depths of nitrogen fertilization: 0 cm(N0), 10 cm(N10), 15 cm(N15), and 20 cm(N20). In the present study, we compared the effects of various fertilizer depths on the root architecture, root anatomy, and the efficiency of water and N use in experiments conducted both in a greenhouse and in the field, with the goal of determining the optimal N fertilizer depth, and thereby greater nutrient and water acquisition. The main results were as follows: 1. Effect of different fertilization depth on root characteristicsThe N15 treatment group had significantly greater root dry weight and root length density than N0, N10, and N20. The root dry weight and root length density of crown roots in 4, 5, and 6 whorls in the N15 treatment group were superior to other treatments. Root length densities of crown roots in 4, 5, and 6 whorls in the N15 treatment group increased 190.21%, 88.75%, and 455.89%, compared to N0, N10, and N20 treatments. 2. Effect of different fertilization depth on root distributionDeep fertilizer adjust root spatial distribution and promote the formation of good root spatial distribution in the soil. The root distribution of different fertilization depth had no significantly different in 0-10 cm soil. N20 treatment had greater root in 10-20 cm soil than others. But N15 treatment group significantly increase root quantity in 20-60 cm soil, with weaken the crowdedness in upper root, thereby promote the growth of root to deep soil and enhance the distribution of root dry weight and root length density in deep soil. N15 treatment improved nutrient absorption in deep soil. 3. Effect of different fertilization depth on root anatomyDeep fertilization increased root cortical aerenchyma(RCA), cortical cell size(CCS), and decreased cortical cell number(CCN), thereby decreased root respiration. N15 treatment significantly enhanced RCA, so root can adapt low hypoxia and suboptimal condition. RCA formation substantially reduces the metabolic costs of soil exploration by reducing root respiration, thereby improving rooting depth, water and nutrient capture. In addition, Aerenchyma formation had allowed remobilization of utilized nutrients to adapt to nutrient deficiencies in the surrounding soil. At the same time aerenchyma increased carbon allocation to roots at the expense of carbon allocation to shoots to require nutrient. Therefore, The RCA and CCS of N15 treatment afford greater respiration space, and absorb enough hypoxia to decreased root metabolic cost and increased nutrient use efficiency to meet plant growth, thereby required high yield and high efficiency. 4. Effect of different fertilization depth on coordination of root and soil nutrientWith the increase of soil depth, the total nitrogen content of soil and root length density of different fertilization depth reduce gradually, however they have close relationship. Deep fertilizer increased total nitrogen content and root length density in the deep soil because of the leaching of nitrogen and root penetration deep soil. The root system distribution concentrated area will appear low nitrogen area in 0-60 cm soil layer, because root absorb soil nutrient. N15 treatment increased root length density in 20-60 cm soil layer, so it enlarge the absorption space. The nutrient of 20-60 cm soil layer can satisfy root absorption and improve nutrient use efficiency and then enhance shoot biomass and improve maize yield. 5. Effect of different fertilization depth on N use efficiencyFertilization at 15 cm resulted in higher photosynthetic rates, leaf areas, and chlorophyll content compared with fertilization at 0, 10, and 20 cm. Deep fertilizer can transfer more nutrient to grain, with improve grain number of area and 1000-grain weight, thereby improve yield. Deep fertilizer enhanced N uptake amount and N uptake efficiency compared to surface fertilization. At the same time N15 treatment significantly increased N uptake efficiency compared to N10 and N20 treatment, thereby prompt nutrient absorption and transfer nutrient to yield at after flowering to improve grain weight. So fertilization at 15 cm resulted in higher photosynthetic rates and leaf areas, lower root respiration, long photosythetic duration, much increased water uptake efficiency, greater shoot biomass, N uptake efficiency and eventually high yield when compared with fertilization at 0, 10, and 20 cm.