Study On Dynamic Change Of Potassium In Soil-Plant System Under Long-Term Fertilization

Long-term fertilization experiment is an important measure in studying evolution regularities of soil fertility and fertilizer efficiency under different fertilization and farming system.This experiment was carried out to study the effects of long-term different fertilization on the content and forms of potassium,soil K-supplying capacity in purple soil and the dynamic change of potassium in Soil-Plant System during the rice-wheat season by using long-term fertilization experiment and laboratory analysis method.And the study which was based on "national soil fertility and fertilizer efficiency long-term monitoring network" built in 1989 was used soil and data persevered for long-term.The purpose was to address the change of potassium fertility,and the effect of long-term fertilization on rice-wheat yield and balance of potassium.The value was to offer scientific basis for rational application of potassium fertilizer and improve potassium fertility of purple soil.The results showed:Contents of total potassium,slowly available potassium and readily available potassium all decreased whether using potassium fertilizer or not using in purple soil after16 years experiment (except for readily available potassium of 1.5(NPK)+M₁).Contents of slowly available potassium and readily available potassium decreased in 16.4mg/kg and 159.0mg/kg on treatments of CK and NP,and decreased in 8.7mg/kg and 109.7mg/kg on the treatments of using potassium fertilizer, respectively.Content of potassium decreased lest on treatment of organic manure combining with chemical fertilizer and content of readily available potassium was equal with before experiment. Content of slowly available potassium decreased 93.3mg/kg.So,the dosages of potassium fertilizer coudle not satisfy rice-wheat need at percent and rice-wheat absorbing potassium of soil caused deficit of soil potassium.Returning the crop straw and applying organic manure could remit the deficit of soil potassium. Either before the experiment(1991)or after(2007),mineral potassium is always the main form of potassium in purple soil and constituted 96.96%of the total amount,the second was nonexchangeable potassium which constituted 2.65%and the other three forms(water soluble potassium,monspecifically absorbed potassium)only constituted 0.39%.The content of total potassium in surface soil was almost aqual to that in subsoil after 16years of rice-wheat rotation.The contents of water soluble potassium,nonspecifically,absorbed potassium,specifically absorbed potassium and momexchange-able potassium were higher in surface soil than in subsoil in all treatments.In treatments free of potsassium the four contents in surface soil were respectively higher more in turn by 11%than those in subsoil.Purple soil has quite strong K-supplying capacity soil.More than 130kg/hm² of total potassium was taken up take rice-wheat,which was came from the soil available and slowly available potassium,the latter were the main potassium source for crop uptake in rice-wheat cropping sequence.We can make out the changes of K-bearing minerals content in the gray desert soil.The soil expansible 2:lclay mineral content increased in treaments free of potsassium(CK,NP),the K fixation rates in NP increased 14%-23%than treament NPK,in a average rate of 18% annually.After a long-term potsassium fertilizer experiment,that exercise influence component of potsssium-bearing mineral.The potassium uptake of wheat changed little and maintained lower level before the jointing stage and increased sharp after the stage.Uptake reached the maximum and occupied 27%of whole season in the booting stage.Uptake decreased slowly after the booting stage and Plant potassium runned off in the ripening stage.The contents of readily available potassium and slowly available potassium changed following with wheat growing on 0-20cm and 20-40cm soil layers,kept the same level in 100d after rice transplanted,decreased substantially for the increase of wheat uptake, reached the minxium in tbe booting stage,and maintained the same level until the blossom stage. The contents of readily available potassium and slowly available potassium increased stage by stage following with the wheat growing.The potassium uptake increased step by step after rice transplanted and the maximum uptake was at the late tillering(rice transplanted after 45d)in the whole stage.The uptake occupied about 30%during 30-45d after rice transplanted.The uptake decreased slowly and kept steady in the ripening stage.The contents of readily available potassium and slowly available potassium changed following with rice growing on 0-20cm and 20-40cm soil layers,kept the same level in 30d after rice transplanted as before rice transplanted and decreased after this stage,and then decreased the minxium in the 45^th day.The contents increased stage by stage and reached the stable level. Applying potassium fertilizer increased content of plant potassium and improved rice-wheat yield.Wheat and rice yield increased by 14.2%and 10.0%in NPK treatment,respectively.Increase of yield was not obvious before 3 years of experiment and promoted stage by stage on the 5^th year. The dosage of 60-75kg potassium fertilizer could not maintain the balance of soil potassium,and chemical potassium fertilizer combining with bamyard manure also was the same condition for content of potassium low in barnyard manure.Returning the crop straw combining with chemical fertilizer could maintain the balance of soil potassium(surplus 329.8kg/hm²).There was an important significance in soil supplying potassium stage by stage for circulate use of straw under the condition of potassium lack in China.