01628nam a2200229 a 450000100080000000500110000800800410001910000190006024500700007926000430014930000090019249000550020152010000025665000150125665000120127165000240128365000170130765000140132465300110133865300300134965300190137915484501993-04-26       1979    bl uuuu     u0uu1 u    #d1 aRITCHEY, K. D.  aPotassium fertility in oxisols and ultisols of the humid tropics.  aIthaca, N.Y.: Cornell Universityc1979  a44p.  a(Cornell International Agriculture. Bulletin, 37).  aIt is possible to study the fate of potassium fertilizer in highly weathered acid soils of the tropics because low amounts of potassium-fixing and potassium-releasing minerals are present. Potassium that is not leached or removed from the field in harvested material remains available on the soil exchange complex. On a Dark Red Latosol in Central Brazil, leaching began to occur only with the addition of 300 kg/ha K as KCl, which is well above the recommemded rate. The potassium content measured in grain crops varied with K status of the soil, from 1,4 percent to 1.9 percent in soybean and 0.23 percent to 0.39 percent in maize. The amount of K that will be exported from the field as grain is easily calculated, and at least this amount of K must be returned to the soil yearly in order to maintain production. If the stover is also removed, its K content should be taken into account as well. Forages removed from the field may contain 1 percent to 3 percent K on a dry-mattrer basis(...)  aAdubação  aCerrado  aFertilidade do Solo  aLixiviação  aPotássio  aBrasil  aLatossolo vermelho-escuro  aRegiao Central