| Phosphorus fertilizer plays an important role in increasing crop yield,but the utilization rate of phosphorus fertilizer in calcareous soil is generally low.Previous studies have found that humic acid can improve the utilization rate of phosphate fertilizer in calcareous soil,but the mechanism of humic acid improving the effectiveness of phosphate fertilizer is controversial.Thus,this experiment adopts the IHSS(international association of humic acid)recommended by humic acid extraction method,extracted from weathering coal humic acid(HA),first by simulating calcareous soil solution environment,explores the add/not adding humic acid effect on the effective phosphorus content and phosphorus(P-Ca)and calcium phosphorus humic acid calcium precipitation(HA-Ca-P),Then,elemental analysis,FITR,XRD,XPS,SEM and EDS were used to explore the composition of precipitation and the binding sites of humic acid and phosphorus,and the release characteristics of P in calcareous soil by P-Ca,HA-Ca-P and humic acid and phosphorus and calcium mixture(HA+P-Ca)were investigated through soil culture experiment.Finally,pot experiment was conducted to verify the mitigation effect of P-Ca,HA-Ca-P and HA+P-Ca on phosphorus deficiency rapeseed,which provided a certain theoretical basis and technical support for the follow-up research and development of humic acid and phosphate fertilizer.The main results are as follows:(1)The laboratory simulation experiment showed that humic acid could significantly increase the available phosphorus content.Compared with the control,the available phosphorus content in the solution increased by 5.1% ～ 25.2% after adding humic acid,and the optimal concentration of calcium ion was 1mmol/L and HA was 20mg/L.When the reaction temperature ranged from 20℃ to 80℃,the available P content increased with the addition of HA,while the available P content of the treatment without HA showed an opposite trend.However,the available P content of the two groups was not significantly affected by the reaction time.Citric acid,oxalic acid and malic acid all promoted the release of available phosphorus in P-Ca and HA-Ca-P,but the effect of P-Ca was slightly better than that of HA-Ca-P.In addition,humic acid solution could promote the release of P from P-Ca precipitates,which was increased by 4.0-5.0 times,2.0-4.7 times and 2.6-3.1 times compared with the control,respectively,in weak acid,neutral and alkaline conditions.(2)The reaction products were characterized and analyzed by different chemical means,and it was revealed that the carboxyl group and hydroxyl group in humic acid reacted with calcium element and phosphorus element,thus it was believed that the humic acid-calcium-phosphorus complex was formed.(3)The soil culture experiment showed that the soil available P content was the highest after the mixture of humic acid and P-Ca.The soil available P content of P-Ca treatment was higher than that of HA-Ca-P treatment from 0 to 40 days,but the available P content of HA-Ca-P treatment was significantly higher than that of P-Ca treatment after 40 days.The treatment of HA only can also increase the soil available P content over time.With the increase of culture temperature and soil moisture content,the available P content of all treatments showed an increasing trend.(4)The pot experiment of rapeseed showed that all treatments could alleviate the phosphorus deficiency in rapeseed.From the effect of HA+P-Ca>Ha-Ca-P>P-Ca>P;Compared with CK and P-Ca,HA+P-Ca treatment increased plant height by 79.0% and 24.1%,root length by 43.1% and 11.7%,leaf width by 201.6%and 72.7%,respectively.Leaf length was increased by 105.1% and 41.5%,biomass by186.7% and 50.0%,SPAD value by 99.0% and 10.6%,and plant total phosphorus by 11.8and 0.35 times,respectively.Compared with HA-Ca-P,plant height,root length,leaf width,leaf length,leaf length,biomass,SPAD value,and total phosphorus content were increased by 6.7%,5.1%,9.8%,8%,8.3%,3.3% and 11.5% respectively under HA+P-Ca treatment. |
