The Regulatory Effect Of Root Pruning On Winter Wheat Yield And Phosphorus Absorption At Different Phosphorus Levels

Studying the effects of root pruning on the yield of winter wheat and its phosphorus uptake under different soil phosphorus fertility and phosphorus application levels will help to develop the desired population density and to judiciously use limited phosphorus resources to achieve sustainable crop production.A pot experiment and several field trials were conducted on a loess soil to study:1)the quantity of phosphorus absorbed by the invalid tiller of winter wheat under different soil phosphorus fertility levels and phosphorus rates;2)the effects of root pruning on the yield of winter wheat and its phosphorus uptake under different soil phosphorus fertility levels and phosphorus application rates.The pot experiment had 5 sets of soils with varying phosphorus levels,which were labeled as F1,F2,F3,F4 and F5 in turn.The soils used were collected from the plots subjected to diverse fertilization treatments for 25years in a long-term experiment on Loess soil.Each of the soil receiving five phosphorus rates,which were equivalent to 0,30,60,90 and 120 kg P₂O₅/ha.The field trials had two soil fertility levels labeled as Low P and High P,which contained Olsen P of 10 mg/kg and 30 mg/kg,respectively.And to each of the soil,three doses of phosphorus were applied,which including control without any P（P0）,60 kg P₂O₅/ha（P60）,and 120 kg P₂O₅/ha（P120）.On each P rate,three root pruning treatments were imposed,which were no root pruning（NRP）,root pruning in winter（RPW）and root pruning in spring（RPS）.The main results obtained are as follow:Pot experiment suggested that the improvement of soil phosphorus fertility increased the maximum tiller numbers,ear formation rates and grain numbers per ear of winter wheat.These three parameters and thousand-grain weights of the winter wheat were also significantly increased with increasing rates of applied phosphorus fertilizer.Therefore,the soil phosphorus fertility and P application rates had considerately effects on the above-ground biomass,grain yield and harvest index of winter wheat;and both of them also showed a significant interaction effect on winter wheat grain yield and aboveground biomass,especially at low phosphorus fertility level and phosphorus application rates.At the same time,increase in soil phosphorus fertility and phosphorus application rates also significantly increased the number of invalid tillers but showed no effect on the valid tillers.The P uptake by aboveground biomass increased significantly with increasing phosphorus application rates in soils where Olsen P less than 15 mg/kg,however,it remained the same where the soil Olsen P larger than 15 mg/kg and P rates were greater than 60 kg P₂O₅/ha.Under the field experimental conditions,regardless of root pruning or not,improvement in soil phosphorus fertility significantly increased the maximum tiller number,valid tiller number,ear number per unit area,and thousand grain weights of winter wheat,therefore,significantly increased the above-ground biomass,grain yield and harvest index.Root pruning along both sides of wheat rows tended to reduce winter wheat grain yield and aboveground biomass in soils with low available phosphorus level,while it had a significant decreasing effect on soils where the Olsen P level was high.Root pruning along both sides of wheat rows significantly reduced the valid number of tillers and earing rates of winter wheat on soils receiving high rates of phosphorus.Root pruning significantly reduces aboveground biomass of winter wheat in low fertility soils thus decreasing phosphorus uptake,especially at the P120treatment.The increase in soil phosphorus fertility and phosphorus application rates significantly increased the number of invalid tillers,which could be substantially reduced by root pruning at winter.The higher the phosphorus fertility level and the amount of phosphorus applied,the earlier the invalid tillers withering away,and the higher the number of invalid tillers under either pot or filed experiment.Root pruning along both sides of wheat rows reduced the density of wheat roots and accelerated the withering of invalid tillers.Under the same soil fertility level and phosphorus application rates,the number of invalid tillers,biomass,and phosphorus uptake were in an order of:RPS>NRP>RPW,and the amount of phosphorus uptake in invalid tillers account for about 0.5%-5%of the total phosphorus uptake in the aboveground biomass.Soil Olsen-P,total phosphorus,and phosphorus activation coefficient all increased with the increasing of phosphorus application rates with.Root pruning tended to increase the content of Olsen-P in soils of lower available P.This study suggested that increasing both soil phosphorus fertility and phosphorus application rate can increase the yield of winter wheat.Root pruning could reduce the invalid tillers,especially at low phosphorus fertility level where it might increase the content of soil available phosphorus by reducing the quantity of phosphorus absorption.The impacts of root pruning on wheat production and phosphorus use efficiency deserve further study.