Differences In The Growth And Development Of Rice On Two Purple Soils And Its Reasons

Paddy soil fertility is the basic resource for sustainable development of rice production.As the key factor of paddy soil fertility,soil nutrient status is the basic index of soil fertility evaluation,which plays an important role in high yield and high quality of rice.At present,many studies have concluded that there is a clear positive correlation between soil nutrient fertility level and crop yield:the higher the soil nutrient fertility level,the higher the crop yield.This is also the theoretical basis of soil testing and formula fertilization.However,our previous experiments and research found that the rice yield and nutrient accumulation in gray-brown mud field with low soil nutrient fertility were significantly higher than those in brown-purple mud field with high soil nutrient fertility,which was inconsistent with the traditional conclusion that high soil nutrient fertility and high rice yield.Based on this phenomenon,this study analyzed and discussed the soil properties and the growth and development of potted rice,and preliminarily explored the causes.The main research contents and results of this paper are as follows:（1）Under the same conditions of fertilization,light,temperature and water management,the effects of environmental and human factors were removed,and the differences of rice yield and nutrient absorption and utilization between NPK field experiment area and PK,NK and NP field experiment area of the same variety of rice in brown-purple mud field and gray-brown mud field were compared.The results showed that PK treatment significantly inhibited rice yield and mineral nutrient uptake in brown-purple mud field and gray-brown mud field.The content of P and K in brown-purple mud field was relatively rich,so the application of P and K fertilizer did not show the effect of increasing rice yield.However,due to the lack of P nutrition in gray-brown mud field,the growth and nutrition of rice were significantly affected by the absence of P fertilizer,and the effect of K fertilizer on it was small.In the same N,P and K fertilization plots,the basic fertility of gray-brown mud field was:organic matter 27.21 g/kg,total N 1.72 g/kg,alkali-hydrolyzable N 188.67 mg/kg,available P 3.94 mg/kg,available K 96.54 mg/kg,which was 41.4%,43.8%,5.6%,65.3%,24.6%lower than that of brown-purple mud field.The rice yield in gray-brown mud field was 9726.86 kg/hm²,13.8%higher than that in brown-purple mud field.Although the total grain number per panicle and 1000-grain weight of rice in gray-brown mud field were 6.2%and 2.6%lower than those in brown-purple mud field,the panicle number per hectare and seed setting rate of rice in gray-brown mud field were 22.1%and 0.6%higher than those in brown-purple mud field,respectively.The accumulation of N,P and K in the shoots of rice in gray-brown mud field were 193.34,39.99 and 202.60 kg/hm²,respectively,which were 25.6%,50.5%and20.5%higher than those in brown-purple mud field.In addition,the partial productivity of N,P and K of rice in gray-brown mud field was 13.9%,13.7%and 13.7%higher than that of rice in brown-purple mud field.The dependence rate of N,P and K of rice in gray-brown mud field was 4.8%,1.5%and 7.1%higher than that of rice in brown-purple mud field.（2）The results showed that rice yield and nutrient accumulation in gray-brown mud field with low soil nutrient fertility were higher than those in brown-purple mud field with high soil nutrient fertility.The absorption and utilization effect of rice on fertilizer in gray-brown mud field was better,and the contribution rate of soil N,P and K to rice nutrition was also higher.This result was inconsistent with the previous study that the higher the soil nutrient fertility,the higher the rice yield.In order to further verify the universality of the results,50 paddy fields were selected in Fengdu County,Dianjiang County and Zhongxian County of Chongqing to investigate the agronomic characters of rice without considering varieties and fertilization.Statistics showed that the average tiller number per nest of rice（1 grain）in gray-brown mud fields in different places was 2 more than that in brown-purple mud fields,and the effective panicle number was 2 more than that in brown-purple mud fields.It was consistent with the field experiment results.（3）The reasons for the differences were explored from the physicochemical and biological characteristics of the two soils.From the analysis of soil physical properties,the soil bulk density of gray-brown mud field was 1.20 g/cm³,and the total porosity was54.35%.The soil in gray-brown mud field had larger volume and smaller total porosity than that in brown-purple mud field.Therefore,the water and air permeability conditions of brown-purple mud field were better.Both soils were dominated by microaggregates in the size range of 0.25～0.01 mm,but the content of microaggregates in the size range of0.05～0.001 mm in gray-brown mud field was 26.3%higher than that in brown-purple mud field,and the content of microaggregates in the size range of 1～0.25 mm was 84.8%lower than that in brown-purple mud field.It indicated that the content of small-size microaggregates that could adsorb,desorb and reserve nutrients in the soil of gray-brown mud field was higher,so the soil of gray-brown mud field had stronger ability to absorb and release nutrients.According to the texture classification table of China,the soil texture types of brown-purple mud field and gray-brown mud field were loam clay and silty sand,respectively.Overall,the sand content of gray-brown mud field was higher than that of brown-purple mud field,while the clay content and powder content were lower than that of brown-purple mud field.Moreover,the soil structure coefficient of gray-brown mud field was 21.5%lower than that of brown-purple mud field,and the dispersion coefficient was 33.5%higher than that of brown-purple mud field,indicating that the soil of brown-purple mud field was more conducive to water and fertilizer conservation.The main mineral types of the two soils were quartz.The content of plagioclase in gray-brown mud field was higher than that in brown-purple mud field,but the content of calcite in brown-purple mud field was rich,and the content of calcite in gray-brown mud field was very low or no.From the analysis of soil chemical properties,the soil nutrient content of brown-purple mud field after rice planting was higher than that before rice planting,and the soil nutrient content of gray-brown mud field after rice planting was lower than that before rice planting.This indicated that rice in brown-purple mud field had low nutrient utilization rate and nutrients accumulated in topsoil,while rice in gray-brown mud field had strong ability to absorb nutrients from soil itself.P accumulation occurred in both soils after rice cultivation,and the available P content in rhizosphere soil was significantly higher than that in inter-row soil,indicating that P activation occurred in rice roots in both soils.The soil p H of gray-brown mud field was low.Under P deficiency stress,the quantity and activity of acid phosphatase secreted by rice roots were increased,and P-containing compounds were activated and bioavailable P was released,thereby improving the availability of soil P.In contrast to brown-purple mud field with high p H,excessive P and large amounts of calcium carbonate in brown-purple mud field may lead to a decrease in the availability of soil zinc.The total amount of NH₄⁺-N and NO₃^--N in gray-brown mud field was higher than that in brown-purple mud field,indicating that more N can be directly absorbed and utilized by rice in gray-brown mud field.From the analysis of the adsorption and desorption characteristics of N,P and K in soil,the adsorption and desorption of N and K in brown-purple mud field were higher than those in gray-brown mud field,indicating that brown-purple mud field had strong adsorption and desorption capacity for N and K.However,the field experiment results showed that the higher N and K nutrients in brown-purple mud field were not conducive to the absorption and utilization of rice.The soil in gray-brown mud field had high adsorption and low desorption of P.The results showed that the soil in gray-brown mud field had greater P capacity than that in brown-purple mud field,and the P in gray-brown mud field was relatively stable,so the release rate of P from soil colloid in gray-brown mud field was more suitable for rice absorption and utilization.From the analysis of soil microorganisms,the total PLFAs of rhizosphere soil and inter-row soil in gray-brown mud field were 10.6%and 66.3%higher than those in brown-purple mud field,respectively.In addition,the absolute contents of each microbial group and each phospholipid fatty acid in gray-brown mud field were higher than those in brown-purple mud field,indicating that there were more corresponding microorganisms involved in regulating soil energy and nutrient cycling and organic matter transformation in gray-brown mud field.The ratio of bacteria/fungi in gray-brown mud field was significantly lower than that in brown-purple mud field,indicating that the soil ecosystem of gray-brown mud field was more stable.（4）The reasons for the differences in the growth and development of potted rice in two soils were further explored.The yield of rice per plant in gray-brown mud field was30.09 g,which was 39.4%higher than that in brown-purple mud field.The reason was that the average tiller number,panicle number,panicle rate,average grain weight per panicle and grain number per panicle in gray-brown mud field were higher than those in brown-purple mud field.The shoot and root dry weight of rice in gray-brown mud field was significantly higher than that in brown-purple mud field at all growth stages.The higher dry matter production in the early stage laid the foundation for the formation of high yield of rice in gray-brown mud field,which was beneficial to transport more photosynthetic products to rice panicles in the later stage.The root/shoot ratio in the middle tillering stage of rice in gray-brown mud field was 17.8%lower than that in brown-purple mud field,indicating that rice could avoid self-consumption caused by redundant root growth under high yield and high efficiency,and coordinated the growth of shoot and root parts.The root diameter,root volume and root activity of rice in gray-brown mud field were significantly higher than those in brown-purple mud field at each growth stage,so rice in gray-brown mud field had stronger ability to absorb water and nutrients.The contents of N and P in different parts of rice in gray-brown mud field were significantly higher than those in brown-purple mud field,and the difference of K content was not significant.Higher nutrient content multiplied by higher dry matter content made the accumulation of N,P and K in all parts of rice in gray-brown mud field significantly higher than those in brown-purple mud field.The contents of IAA,ABA,GA and CTK endogenous hormones in roots and leaves of rice in gray-brown mud field were higher than those in brown-purple mud field at the early and middle tillering stages,and the IAA/CTK ratios in roots and leaves of rice in gray-brown mud field were lower than those in brown-purple mud field,which increased tillering of rice in gray-brown mud field,promoted the distribution of assimilates to the shoots,and increased yield.The yield of rice in gray-brown mud field was higher than that in brown-purple mud field.The main reasons were that the rice in gray-brown mud field had a smaller root/shoot ratio at the middle tillering stage,a higher endogenous hormone content in roots and leaves at the early and middle tillering stages,and a larger root volume and stronger root activity at all growth stages,which made the rice in gray-brown mud field have higher tillering,effective panicle number and panicle rate than that in brown-purple mud field.In addition,the higher dry matter production and nutrient accumulation at the early stage ensured the formation of high yield of rice in gray-brown mud field at the late stage.From the perspective of soil nutrient content,bulk density,total porosity and mechanical composition,brown-purple mud field had richer nutrients,better water and air permeability conditions,higher clay and silt content,and higher structural coefficient,which was conducive to water and fertilizer conservation.However,from the perspective of soil microaggregates,adsorption and desorption characteristics of N,P and K,and microorganisms,the ability of gray-brown mud field to absorb and release nutrients was more favorable,and the rate of soil colloid releasing P was more suitable for rice absorption and utilization,and the total amount of microorganisms was high,and the ecosystem was more stable.In summary,the results of the above experiments show that the soil nutrient content is currently used as an important indicator to evaluate soil fertility,and whether the fertility differences between different soil types are comparable?Whether the existing soil available nutrient determination methods truly reflect the plant availability of nutrients?Soil as a complex organism,which factors to choose to reflect soil fertility needs more in-depth research and a lot of practice accumulation.