Effects Of Long-term Fertilization Regimes On Potassium Status Of Lou Soil And Potassium Use Efficiency

Potassium is a necessary element for plants. It plays an important role in increasing cropyield quantity and quality and intensifying stress resistance by reasonable potassiumfertilization. The soil in North of China has been rich in potassium and crop is planted withoutpotassium fertilization. This will be inevitable to deplete soil potassium pool, at present thereis lack of effective way to evaluate this depletion. This study employed a20-year long-termfield experiment on loess soil to investigate soil potassium status and potassium use efficiencyunder wheat-maize crpping system, The experiment included nine treatments, which wascontrol (CK, no any nutrient input), N, NK, PK, NP, NPK, straw plus NPK (SNPK) andmanure plus NPK (M1NPK and M2NPK). The main results obtained were as follows:1. Compared with NP treatment, NPK application did not significantly increase cropyields. The result implied that potassium was not a limiting factor in crop production of loesssoil. The K balance sheet showed that except for the NK, PK and M2NPK treatments, thetotal K uptake by crops exceeded the quantities of total K applied to the soils, especiallyunder NP treatment. Soil available potassium contents were significantly increased by thelong term addition of potassium containing fertilizers, but it remained unchanged on thetreatments without K addition. In addition, applying K fertilizer had positive trend on slowavailable K concentration. The potassium recovery efficiency and agronomic efficiency forwheat ranged from4.5to38.3%and from1.58to3.73kg/kg, respectively, and for maizeranged from13.71to61.92%and from0to9.10kg/kg, respectively.2.The relationship between potassium quantity and intensity (Q/I) showed that activityratio after potassium equilibium (AR_e^K) ranged from1.01×10^-3to11.57×10^-3(mol/L),the lowest value under NP treatment. This indicates soil potassium releases easily to be availablefor crop use. And immediate available K (-ΔK⁰) fluctuated from0.149to0.180cmol/kg, thelowest value also under NP treatment. The potential buffering capacity (PBC^K) withoutapplying potassium ranged from134.7to147.2, which was higher than PBC^K(90.8¹12.6)with application of potassium. Free exchange energies (-ΔG) for the replacement of calciumand magnesium with potassiumranged from11.05to17.09KJ/mol in all treatments, inaddition, the amounts of–ΔG in treatments without K fertilization were higher than thosewith K fertilization. These results indicate that potassium of loess soil depleted seriously, butpotassium in soil still remained high content in available form.3. The long-term fertilization had no significant effect on soil total K content. Thecontents of non-exchangeable K (Mactotal K) and easy extractable K (Step K) particularly thelater, were substantially lower than their initial values, which suggests that Step K andMactotal K could be used as an indicator of K depletion for the investigated soil. The contentsof Mactotal K and Step K did not significantly change in20-60cm soil layer. Whether or notapplication of K fertilizer, the content of soil K increased significantly with soil depth deeperthan60cm, this might indicate that K leaching from top soil layer to deep layers contributed alarge portion of potassium depletion in plough layer.All in all, although the content of potassium was rich in Lou soil, the potassium depletedseriously with time, especially nonexchangeable K. Therefore, long-term application ofmoderate manure and crop straw return to the soil is necessary to maintain K fertility and landsustainable productivity.