Study On Population Quality And Individual Physiology Function Of Super High-yielding Maize (Zea Mays L.)

China is facing the problems of irreversible decrease in arable land, rapid population growth and stagnant output of crop. Fortunately, the super high-yielding crop breeding and production is put forward to improve the critical situation. However, the mechanisms of synchronous improvements on population quality and individual function of super high-yielding maize were not clearly understood. The goal of the paper is to help us to understand the potential of maize and provide the basal information and techniques for maize yield improvements in future.The field experiment was carried out from 2005 to 2007 in loam soil located at the National Maize Engineer and Research Center (Shandong province, China). In this experiment, the maize hybrids DH3719 was used to compare the yield of 21000 kg ha-1 via super-high yielding cultiviation system (SYCS) to the yield of about 9000 kg ha-1 via conventional cultiviation system (CCS). The population quality and individual items, including population uniformity, harvest index, grain/leaf area, photosynthetic parameters, anti-oxygen performances and mass nutrition elements (nitrogen, phophorus and potasium) uptake and utilization were investigated. The main results and significant conclusions were as follows:1. Population qualityThe yield per degree-day of DH3719 via SYCS was higher than that via CCS. The maximum crop grown rate (CGR), photosynthetic accumulation before maximum CGR and initiative filling potential of SYCS were significantly higher than CCS, and the peak of CGR in SYCS occurred earlier than CCS, accordingly, the active grown time of SYCS was 15 days longer than CCS. SYCS had higher capability to produce grain than CCS with the ratio of grain and leaf area of over 0.25 kg m-2, which showed it's possible to improve the source by enhancing sink. The harvest index (HI) of SYCS was higher than that of CCS with 0.532-0.542, revealing the higher population quality, higher photosynthesis efficiency and stronger photosynthate partitioning capabilities under high planting density.It is one of the most important targets to improve the population uniformity and population quality in the future maize practices for super high yield. In our experiment, the variance on kernels per ear was the highest in the seven agronomy items (plant height, stem diameter, ear height, rows per ear, grains per row, ear diameter), then came the diameter of stem, so high planting density remarkably affected the ear and stem growth and development. The variance on kernels per ear was contributed by rows per ear and kernels per row, especially kernels per row, therefore, increasing uniformity of rows per ear by regulating the carbon-nitrogen metabolisms and decreasing grain abortion could increase density of kernels, and then increase the yield of maize.SYCS needs more fertilizers than CCS. The yield of SYCS was 2.5-3.5 times higher than CCS, while the fertlizers for SYCS should be more 3 times than CCS. When produced 100 kg grain, the absorption of N, P2O5 and K2O were 2.00 kg, 1.579 kg and 1.92 kg in CCS, respectively, but 2.10 kg, 1.79 kg and 3.74 kg in SYCS. Even more, among the 3 fertilizers, SYCS need more K2O and P2O5 than CCS, but less N than CCS.2. Individual physiological functionThe individual biomass per degree-day in SYCS was higher than that in CCS. Compared with CCS, SYCS was characterized with late grain filling, gentle change of grain-filling rate, and long active grain-filling period. Not grain-filling rate but long active grain-filling period contributed high yield for SYCS, which could be seen from over 14 days longer of active grain-filling period in SYCS than CCS. Prolonging the grain-filling time was essential to obtain super high yield in maize, while higher grain-filling rate may be the signal of rapid senescences in the anaphase of grain weight formation, not the symbol of high-yielding.Improvement in photosynthesis for SYCS was mainly by long high-photosynthesis duration, not by the high photosynthesis rate during grain-filling. For maize, the strategy of capturing more light radiation under high planting density was by enlarging the leaf area, not by increasing the photosynthetic rate. The significantly positive relationship between photosynthetic rate and stomatal conductance revealed it was important for high yield to alleviate the abiotic stress, such as drought, nutrition deficiency, disease and insect pest etc. The diurnal trends of photosynthesis on 25 and 45 days after anthesis indicated the photosynthate accumulation unit in SYCS was not different from CCS in the prophase of kernel development, nevertheless, SYCS was significant higher than CCS in the phase of grain weight formation. So it is necessary to regulate the confliction between photosynthetic rate and photosynthesis duration for super high yield.One reason for higher yield of SYCS is the higher nitrogen concentration in leaves after anthesis, which would maintain the higher physiological function and delay the leaves senescence after anthesis. The 30th day after flowering was boundary for the difference of nitrogen concentration in leaves between SYCS and CCS. SYCS had high anti-oxygen capability during grain filling, the reactive oxygen cleaning was mainly through CAT and POD system, especially in the 50th day after anthesis. The degree of membrane lipid peroxidation was lower in SYCS than in CCS, especially the 50th day after anthesis. The high total ezyme activities in SYCS were not owed to its specific activity but to the high functional soluble protein amount.3. Synchronous improvement of population structure and individual functionThe theory of"Synchronous improvement of population structure and individual function"was established. The core of it was that: the over-compensation effects of biology and ecology occurred in crop population spatial structure, coinstantaneously the over-compensation effects of biology and physiology occurred in crop individual temporal scale.This theory integrates the planting density and row distance scheme, irrigation and fertilizer management. On one hand, planting density increment compensated the reduction of individual. On the other hand, individual function with high activity increment over-compensated the increase of population structure. The technological practices included choosing hybrids by intending goal yield, obtaining high density by plant type, ensuring the population uniformity by alternating row and diagonally sowing, and enhancing fertilizers and water inputs after anthesis, therefore, the photosynthesis and grain weight were improved and plant senescence were delayed. Two effective approaches of"structural exploration"and"functional exploration"for exploring crop yield.4. Quantitative items of super high-yielding maizeThe quantitative items of super high-yielding maize with yielding potential over 15000 kg ha-1 were explored in our experiment. The ideal system of yield components was: harvested ears≥78000 ear ha-1, kernels per ear≥600, 1000-kernel weight≥340 g, ear weight≥200 g. In the optimum zone planted anti-lodge hybrids and without lodge occurring, the ideal system of yield components was: harvested ears≥90000 ear ha-1, kernels per ear≥540, 1000-kernel weight≥320 g, ear weight≥200 g.