The Research Of Effects Of Different Planting Densities On Maize Root Structure

As strong root systems are the basis of high-yield crops, root morphology and spatial distribution are the important factors that affect nutrient’s absorption. Most agricultural practices such as irrigation, fertilization affect the growth, development and functions of roots on the ground at first, and eventually affect the production. Roots are vital to the quality and production of crops.Root’s growth and spatial distribution in super high-yield cultivation is particularly important, and especially all high-yield cultivation techniques depend on high density. However, high density makes the individuals of crops competing with each other so that the plant and root’s growth is inhibited. Relevant studies have showed that high density technique often leads to premature lodging and other problems, resulting in yield reduction in different degrees, and then limiting the yield-increasing effect of high-density. Besides, maize’s root system grows vigorously at the silking stage which is also the critical period to dry matter accumulation on the ground and yield formation. This research analyzes root system with drill method to study the root’s main index in 0-50cm deep in soil at the silking stage under different density conditions together with the target on the response of ground to densities.2.The main results show as follows:1.The regularities of root distribution 0-50cm deep in soil at the silking stage of maize under the condition of different planting densities are:(1) The overall distribution regularity:with increasing planting density, the whole roots stretch deeper in the soil, and root weight of unit volume and total root volume increase, while root length as well as surface-area of unit volume decreases. (2)The vertical distribution of root systems:all characters of the systems are gradually weakened as they go deeper in soil layers, especially obvious the extent of the weakening is in the layer of 0-20cm, and the extent, when they go deeper, will be less. (3) The horizontal distribution in the different layers respectively:in the 0-10 cm of soil layer, as the planting density intensifies, root weight and root volume increase, while root length and root surface area are on the contrary. In the soil layers under the ground surface between 20-40 cm, the indicators are smallest under low density and there is no apparent rule between middle density and high density.And in the layers between 40-50 cm, the indicators increase as the density intensifies.2. Influences of different planting densities on the aerial parts are listed below:(1) The leaf area index(LAI) changes in a uni-modal curve as the development progress goes on, and reaches the peak at the stage of silking. In the same period of duration, LAI goes up with the increasing density, and the gap between medium density and low density is apparently larger than that between medium and high density. Besides, as the development progress moves on, the gap among different densities enlarges, which hits the climax during the silking phase and then declines. (2) The effects of different densities on yield and yield component are that medium density leads to the highest yield. Among all that influences the yield, the spike number, and hundred-grain weight have a larger effect on the yield. The spike number goes up while the hundred-grain weight goes down as the density intensifies. The gap of the number of kernels per spike under the conditions of low density and medium density is small, but both respectively more than the number under high density.(3) During the pustulation period, under the conditions of different densities, the grain quantity and quality that unit leaf area can bear decline as the density increases, especially for the quality.3. The correlation between the part above the ground and the characteristics of root systems under different planting densities::(1) The root-system-related index of unit leaf area decreases with the increasing density. (2)The root system index of unit grain weight takes on a regularity as:low density>high density>middle density.(3) The change rule of root shoot ratio is:high density>low density>medium density.Conclusion:1.Root growth of maize plants, primarily changes through regulating the surface root system to adapt to the changing density. Roots use deep soil moisture, nutrients, and stable environment around roots to resist the strong competition brought by high density.2.The optimal density under current fertilizing conditions of this maize plant is around 75,000/hm2. Increasing effective panicle number of unit area and the number of every spike at the same time is an effective guarantee of realizing high production.Judging from the current situation, graining the number of every spike is a major factor of limiting effect of density on the high-yielding.3.The responses of root system and canopy growth to group competition are synchronized. They both increase as the density decreases, however, aerial parts of competitive intensity are greater than the underground parts.4. High density leads to the highest yield, and the root-system index of root shoot ration and unit grain weight under medium density is the lowest, which means that the root configuration and canopy structure under medium density is excellent, only less root systems can meet the needs of the plant’s development, and the potentials of root systems need to be explored.