Effect Of Straw Returned To Soil On Crops Yield And Soil Potassium Under Wheat-Maize Rotation System

The experiments were conducted from October2008to October2011in the experiment station ofNational Laboratory of Soil Testing and Fertilizer Recommendation of Chinese Academy ofAgricultural Sciences, which is located in Langfang city of Hebei Province. Four treatments weredesigned as a randomized complete block with three replications. Treatment1: no straw returned and noapplication of chemical potassium fertilizer (denoted as NP); treatment2: no straw returned andapplication of chemical potassium fertilizer (represented by NPK); treatment3: crops straw returned andno application of chemical potassium fertilizer (represented by NP+St); and treatment4: crops strawreturned and application of chemical potassium fertilizer (represented by NPK+St). Under the summercorn and winter wheat rotation system in North China Plain, a field experiment with six crops seasonsand three rotation systems was carried out to investigate the effects of crops straw returned to soil andapplication of chemical potassium fertilizer on the crops yield, K balance in soil-crops system, and theratio of chemical K replacement by straw. Meanwhile, the topsoil of0~20cm in the experiment wassampled to extract different forms of K by several solutions and study the distribution characteristics ofthe different forms of K in soil; to study the fixation ability of different concertrations of additive K; andto study the release characteristics of nonexchangeable K by the method of centrafiuge-balance with0.01mol/L CaCl2and0.01mol/L oxalic acid extractant. The main results as following:Compared with treatment NP, there were significant yield increasing in treatments NPK+St, NPKand NP+St, the optimal treatment was NPK+St, the yield of winter wheat and summer corn were4148.0and6416.1kg/hm~2, which increased by13.3%and17.4%in contrast to treatment NP, respectively.Application of potassium fertilizer could increase wheat and corn yield by318.9and688.7kg/hm~2, andthe yield increment was8.6%and12.4%in wheat and corn season respecitively. Generally speaking,the yield increase of corn was greater than that of wheat. Crops straw returned to soil could increasewheat and corn yield by169.3and259.8kg/hm~2, and the yield increment was4.5%and4.5%in wheatand corn season, respecitively. The ratio of chemical K replacement by corn straw was25.2%in wheatseason, and that by wheat straw was20.3%in corn season. Compared with treatment NPK, there hadhigher recovery efficiency, agronomic efficiency and partial factor productivity from applied K intreatment NPK+St.In contrast to treatment NP, treatments NPK, NP+St and NPK+St significantly increased watersoluble K, nonspecific adsorption K, nonexchangeable K, mineral K and total K content; however, therewas no significant effect on specific adsorption K. The available K, slow-release K and total K in tillagesoil with crops straw returned to soil or potassium fertilizer application were significantly higher thanthose in treatment NP, and which increased with the growing seasons. Compared with the basic soil atbeginning of this experiment, soil available K content in treatment NP keeps declining. Crops strawreturned to soil and application of chemical potassium fertilizer could decrease the ratio of mineral Kaccount for total K in soil. In comparation with the application of potassium fertilizer, crops straw returned to soil significantly increased the ratio of water soluble K, nonspecific adsorption K,nonexchangeable K and mineral K account for total K.Crops straw returned to soil and application of chemical potassium fertilizer significantly increasedtotal K absorption, except the treatment NPK+St, some other treatments with lower K input had lowtotal K absoption and caused soil K deficiency, espspecially in treatment NP. Deficit of K in soil withtreatment NP was the highest, the total deficit of K2O was720.1kg/hm~2after three years; however,there was still deficit of K2O in soil with treatment NPK, which was497.8kg/hm~2after three years;treatment NP+St could nearly maintain soil K balance, only had deficit of K2O by63.5kg/hm~2; soil Kwas surplus in treatment NPK+St, which was248.9kg/hm~2of K2O. The indexes of K balance were1.26,0.42and0.92in treatment NPK+St, NPK and NP+St, respectively, which indicated that except fortreatment NPK+St, indexes of K balance in other treatments were less than1.After3years crops growing, when the concentrations of additive K were ranged from400to3600mg/L, crops straw returned to soil or application of chemical potassium could significantly decreasedthe amounts of additive K fixed in soil, and the fixation ability of K increased with the concentration ofadditive K increase, whearas the proportion of fixation decreased. At the same concentration of additiveK, the K fixation amounts were in the following order: NPK+St<NPK and NP+St<NP. Compared withthe start of basic soil, soil K fixation declined in treatment NPK+St, whearas increased in treatmentsNPK, NP+St and NP, the increament was high in treatment NP. Both crops straw returned to soil andapplication of potassium fertilizer could influence the content of soil available K, slow available K, soilorganic matter, K+saturation (KSR) and CEC, therefore, which influence the fixation ability of additiveK.There were similar characteristics of soil nonexchangeable K release in two extraction solution of0.01mol/L CaCl2and0.01mol/L loxalic acid, the maximal amounts of soil nonexchangeable K releasehad the trendicy of NPK+St>NPK>NP+St>NP. Compared with the basic soil, there was significantdifference in all treatments, the maximal amount of soil nonexchangeable K release in treatmentNPK+St was found after241hours in two extraction solutions, which increased by9.2and21.5mg/kg,respectively; there was little change in treatment NPK and NP+St; however, the maximal amount of soilnonexchangeable K release in treatment NP after241hours with two extraction solutions decreased by8.8and61.5mg/kg, respectively. Soil nonexchangeable K release could be well discribled by first-orderrelease kinetic equations. According to different K input treatments, the parameters of release rate ofnonexchangeable K in two different extraction solutions were NPK+St>NPK>NP+St>NP or NPK+St>NP+St> NPK>NP, and the release amounts and rates of nonexchangeable K, and soil K supplyingability were greater in high K input treatment. The release amounts and rates of nonexchangeable Kwere small in treatment NP, and soil K supplying ability was very limited.