Root Pruning Affects Winter Wheat Performance And Phosphorus Uptake

Wheat is one of the most important food crops,one of the key to its high yield is the number and quality of tillers.The application of phosphorus fertilizer or improving soil phosphorus fertility can largely promote wheat tillering and form valid tillers,but high phosphorus application or soil phosphorus level also increases the number of invalid tillers of winter wheat,resulting in invalid tillers and valid tillers competing for soil phosphorus and reducing phosphorus use efficiency.Study on the effect of root pruning on winter wheat yield and phosphorus uptake under different phosphorus levels is of great significance for high and stable yield of wheat and efficient utilization of soil phosphorus.Pot experiment and field experiment were conducted on Lou soil to study the effects of phosphorus level and root pruning on winter wheat yield,root density,invalid tillers,phosphorus uptake and phosphorus use efficiency for grain.The pot experiment had 5 sets of soils with varying phosphorus levels,which were labeled as F1,F2,F3,F4 and F5 in turn.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 30mg/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）.At each P rate,three root pruning treatments were imposed,which were no root pruning（CK）,root pruning in winter（RPW）and root pruning in spring（RPS）.The main results obtained are as follow:Phosphorus fertilizer,phosphorus rate and their interaction had significant effects on grain yield,biomass,harvest index,crop phosphorus uptake and phosphorus use efficiency for grain.The agronomic threshold of Olsen P for winter wheat obtained from pot experiment was24 mg/kg.When the soil Olsen P content was lower than 24 mg/kg,phosphorus application had obvious yield-increasing effect on wheat.The soil Olsen P content was 28 mg/kg when the phosphorus uptake of wheat was the highest.With the increase of soil Olsen P content,the phosphorus uptake of crops did not change.When the soil Olsen P content was 33.75-35.67mg/kg,the utilization rate of wheat phosphorus fertilizer reached the highest.However,with the increase of Olsen P content in soil,the utilization rate of phosphorus fertilizer in wheat decreased.So the best range of soil Olsen P content for high yield and phosphorus efficient utilization of potted winter wheat is 33.75-35.67 mg/kg.In the field experiment,whether root pruning in winter or spring can ensure stable crop yield,but it will reduce root redundancy and reduce root density.This effect is more obvious in high phosphorus level soil,and the opposite results appear in low phosphorus level soil.Root pruning not only reduces invalid tillers,but also reduces valid tillers.However,grain number per spike and grain weight of wheat are significantly increased,thus ensuring that crop yields are not reduced.Both root pruning methods can reduce the biomass of invalid tillers and phosphorus uptake,and the reduction effect is more obvious with the increase of soil phosphorus level.Winter root pruning not only reduced the phosphorus uptake by invalid tillers of wheat,but also increased the phosphorus use efficiency for grain,which may be due to the increased uptake of soil phosphorus by main stem and valid tillers and their transfer to grain after lateral root pruning.The four phosphorus fractions in BBP method can comprehensively evaluate the availability of soil phosphorus.Phosphorus fertilizer can significantly improve the content of four phosphorus fractions based on bioavailability in soil,and the content of four phosphorus fractions was positively correlated with the content of available phosphorus.In this study,root pruning had no significant effect on soil Citrate-P,HCl-P,Enzyme-P content.Root pruning in winter reduced soil Ca Cl₂-P content in high phosphorus soil,and increased soil Ca Cl₂-P content in low phosphorus soil,which was consistent with the effect on root density.Because root pruning reduced the amount of phosphorus absorbed by invalid tillers and weakened the ineffective absorption of phosphorus by crops,there was a trend to improve the content of available phosphorus in soil.This study showed that root pruning could not only ensure high and stable yield of wheat,but also reduce ineffective phosphorus uptake and improve phosphorus use efficiency,which was of great significance for efficient utilization of soil phosphorus.