Effect Of Silicon And Phosphate Combined Applications On Nutrients Accumulation And Utilization And Yield Formation In Maize(Zea Mays L.) Under Low Phosphorus Stress

Silicon, as an important element for plants, has an ability to improve crop growth, increase the resistance to biotic stress (pests and diseases) and abiotic stress (salt damage, toxicity of heavy metals, drought stress, nutrient deficiency or excess stress, etc.), and improve crop yield and quality through participating plant metabolism and physiology. Phosphorus, as one of the three key plant macronutrients, also has an ability to improve crop yield and quality significantly. Phosphate fertilizer utilization efficiency was reduced obviously because of applying a large number of phosphate fertilizers, which will result in serious consumption of phosphate resources. It was reported that silicon can improve the effectiveness of soil phosphorus, but it was the lack of depth study of interaction mechanism between silicon and phosphorus in saving cost, increasing yield and increasing benefit in maize (Zea mays L.).To study the effects of silicon and phosphorus combined applications on root characteristics at seedling stage, photosynthetic characteristics during key growth stages, content variations of soil available silicon and soil available phosphorus, nutrient (N, P, K and Si) absorption and utilization, dry matter accumulation and distribution, yield and yield components of maize under low phosphorus stress, cultivars of ZH2 and ZH115 were studied and analyzed by exploring a series of laboratory and field experiments. In the laboratory (2014), a series of solution and sand culture experiments were set up, the experimental treatments were applied in a split plot design, the main plots were three P levels:P concentrations of the culture medium were 1 mmol·L-1,0.1 mmol·L-1 and 0.01 mmol·L-1, named A1, A0.1 and A0.01 respectively, and Si was the subplot with three levels: 1.5 mmol·L-1,0.75 mmol·L-1 and 0 mmol·L-1,and named Si1.5) Si0.75 and Si0 respectively. While the field experiments were conducted at two locations. The first field experiment in Jianyang (2014 and 2015) were also applied in the split plot design, the main plots were two maize cultivars:ZH2 and ZH115. Four fertilizer combinations were the subplots: application rate of phosphate fertilizer (P2O5) and silicon fertilizer (SiO2) all were 0 kg·ha-1, only application rate of Silicon fertilizer (SiO2) was 75 kg·ha-1, only application rate of phosphate fertilizer (P2O5) was 60 kg·ha-1, application rate of phosphate fertilizer (P2O5,60 kg·ha-1) and Silicon fertilizer (SiO2,75 kg·ha-1), named P0Si0, P0Si75, P60Si0 and respectively. The second field experiment in Zhongjiang (2015), were applied the same design as well as the experiments in Jianyang, the main plots were four levels of phosphate fertilizer applications:0 kg·ha-1,30 kg·ha-1,60 kg·ha-1 and 90 kg·ha-1, named P0, P3, P6 and P9 respectively, and three levels of Silicon fertilizer applications were the subplots:0 kg·ha-1,37.5 kg·ha-1 and 75 kg·ha-1, named Si0, Si37.5 and Si75 respectively. The main results were as follows:(1) In solution culture experiment and sand culture experiment in 2014, the results showed that root dry weight, total root length, root surface area, leaf area, net photosynthetic rate, intercellular CO2 concentration, open degree of PS Ⅱ reaction center, the efficiency of light energy transformation and electron transfer of ZH2 and ZH115 were all were increased by supplying Si under the treatment of A1 or A0.1. These changes by adding applying Si would lead to decrease of photo inhibition, improve the heat dissipation capacity of leaf, and increase dry matter accumulation, which were accommodated the root low phosphorus stress environment. The best Si concentration for root growth was 0.75 mmol L-1 under the treatment of A1, and 1.5 mmol L-1 under the treatment of A0.1, but there was no significant improvement on root growth by adding applying Si under the treatment of A0.01.The same results were also found in field experiments in Jianyang and Zhongjiang. In low available P content of soil, the increase of leaf area index and net photosynthetic rate, and the decrease of transpiration rate were all significant under the treatments of P0S175, P60Si0 and P60Si75, while the increase or decrease of above indexes under the treatment of P6oSi75 was the greatest in these treatments. With lower in available P and available Si contents of the soil in Jianyang and Zhongjiang, the photosynthetic capacity could be improved significantly by applying silicon fertilizer (SiO2) 75 kg·ha-1.(2) In solution culture experiment and sand culture experiment in 2014, N, P, K and Si accumulation of root, stem and leaf, N, P, K, and Si distribution ratio of stem and leaf, and N, P, K, and Si dry matter productivity all could be increased, while N, P, K, and Si distribution ratio of root was decreased by applying Si under the treatment of A1 and A0.1. In low available P and Si contents of soil in Sichuan basin hilly upland, the soil phosphorus pools were activated, the amount of adsorption of phosphate fertilizer by the soil was reduced, and the amount of soil phosphorus desorption was increased by applying silicon fertilizer. Contents of soil available P and available Si in 0-20 cm and 20-40 cm, and N, P, K, and Si accumulation of maize at jointing stage, silking stage and maturity stage, N, P and K apparent translocation amount of stem and leaf, accumulation efficiency and partial factor productivity of nitrogen fertilizer, phosphate fertilizer, potassium fertilizer and silicon fertilizer, and P utilization efficiency all were improved significantly under the combination of applying silicon fertilizer together with phosphate fertilizer.(3) In low available P contents of soil of Sichuan basin hilly upland, it was that the grain yield of maize was increased 6.32%～13.56% by applying silicon fertilizer (SiO2) 75 kg·ha-1,20.56%～62.46% by applying phosphate fertilizer (P2O5) 60 kg·ha-1,and 30.61%～80.13% by applying silicon fertilizer together with phosphate fertilizer. In field experiments of Jianyang and Zhongjiang, dry matter accumulation of population in main growth stage and grain yield of maize were increased, grain filling and fruiting in later growth stage was promoted, dry weight ratio of different organs of maize in later growth stage was optimized under the treatment of phosphate fertilizer (P2O5) level was 60 kg·ha-1 and silicon fertilizer (SiO2) was 75 kg·ha-1. In Jianyang and Zhongjiang, the grain yield of maize would be kept invariant and even increased by applying silicon fertilizer (SiO2) 75 kg·ha-1,once the phosphate fertilizer (P2O5) level was decreased from 90 kg·ha-1to 60 kg·ha-1, or less to 30 kg·ha-1.In summary, there were significant interaction effect and synergistic effects between phosphorus and silicon on nutrients accumulation and utilization and yield formation in maize. In non-severe phosphorus deficiency conditions, the ability of nutrient absorption and dry matter production were enhanced to alleviate low P stress. The ability of soil in supplying P and Si, the accumulation and utilization of N, P, K and Si of plant, dry matter accumulation and photosynthetic production could be improved in the early growth stage; N, P, and K translocation and reutilization of leaf and stem and dry matter distribution rate of each organ could be optimized in the later growth stage, grain filling and fruiting and yield increased finally by applying P fertilizer together with Si fertilizer when available P content of soil was low in Sichuan basin hilly upland. In our experiment area, the optimum fertilizer combination were at 60 kg·ha-1 phosphate fertilize(P2Os) application rates and 75 kg·ha-1 silicon fertilizer(SiO2) application rates.