We have knowledge on the various mechanisms of N loss from soil water plant system. We have also data on the amount of N loss from different types of soil and cropping systems. But have we any data on the amount of K loss from the different cropping systems or different soils? Which fraction of K is lost much what are the mechanisms of loss?
Dear Aminul,
For determination of leaching loss of K from soil profiles of agricultural fields you may use the following method:
(1) Install piezometers (made of PVC tube with porous ceramic cup fitted at the bottom and topend kept open) in the field with their bottom placed at different depths, say at 30, 60, 90 and 120 cm. Open top of the piezometers should be kept above the field surface and closed to avoid entry of water or any other material from outside into the pipe.
(2) Draw leachates collected in the piezometers periodically by using hand operated suction pump, and analyse them in the laboratory for water soluble K .
(3) From the data on water soluble K at different depths at different period, you can work out the movement and extent of leaching loss of applied K in/from the soil profile.
We have successfully used this method for studying movement and leaching of K from rice fields in canal command area of Odisha (in eastern India).
We observed accumulation of K in the deeper layer of soil profile due to long-term rice cultivation. How they accumulate in that layer? Is it leaching loss or any other mechanism like exchange with other ions?
Unlike Nitrogen Potassium is not occur in q gaseous state or phase. Unlike Phosphate which is also not found naturally in gaseous state but solubilizes as a anion, Potassium mainly is found in soluble and mobile and active form as a single charged Cation. Like Ammonium this will make it able to be complexed with clay and organic matter. If the soil is sandy and low Potassium into the subsoil. Both Potassium ans soluble fine clay moves or eluviates. Clay eluvation may created limiting conditions of high compacted clay. The famous compact subsoils and plow pans are examples. Excessive nutrient in cationic forms will take residence in these sites. The ability to accumulate soil organic matter is often limited by insufficient clay and cationic bridges to stabilize soil organic matter into an organomineral complex. In sandy soils the use of fine materials in the subsoils may be useful for remediating a organic matter deficient top soil. Clay by itself can have constraint for its insufficient porosity to provide adequate aeration for optimal rooting but with the complexing with organic matter these constraints can be overcome. The ability to bioengineer clay carbon complexes through cationic stabilization is a potential mechanism to greatly reduce rapid loss of soil organic matter from decomposition and thereby counteract greenhouse gas elevation and climate issues.
Yes Paul Hepperly, the metallic K does not lost as gaseous from the soil system. This K remains in soil exchange site or in soil solution or entrapped in the space of clay lattice as K+ ion. This ion can undergo in exchange with other cation like H+, Ca2+, Mg2+ etc. in the sub soil and can be accumulated there.
Under wetland situation exchangeable K is subject to leaching with water by exchange with hydrogen and other cations, and leaching losses in permeable soil in humid regions must be replaced. If clay is abundant in the sub-soil, K leached from the surface soil may become concentrated there in exchangeable and fixed form. High rainfall and warm temperature in tropical rice growing area have accelerated the release and leaching of soil K over time.
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