BOLETIM DA FACULDADE DE CIÊNCIAS AGRÁRIAS DO PARÁ, n. 17, 1988.

Abstract

1) An experiment was conjucted on laboratory convitions withfour replications, on a "How Humic Gley " soil from the varzea of Guama river. being the soil solution extracted periodically. The redox potential was measured by the use of electro desfixed on the plots. The pH, Eh, P, V, Na, Ca, Mg, Cv, Al, Zn, Mn and Fe of the soil solution were determined. The maximum reduction was obtained on 240 mV the pH was established around 7,0. The P did not show regular variation as well as most of the measured. The found rates were very much lower then the total rates of the available soil.

2) In soils samples taken different profiles of seven soils groups of the Bazilian Amazon Region, their organic, total. Ca, Al, Fe and water soluble phosphates were determined. It was observed that the organic phosphate fraction is small and in 70% of the soils it represents more or less 20% of the total P present. The largest inorganic P fraction correspond to the occluded and reductant soluble P, only indirectely determined here. The C/P and N/Porganic rations found were rater variable, reflecting the heterogeneity of the soils studied. The average for two rations ate 217 and 15,7. Based on these results, it is believed that the use of phosphatic fertilizers could result in increased production.

3) The Terra Roxa Estruturada of Amazônia are dominantly eutrophicsoils, deep, wherethe CEC present with variation in average between 8,03 and 18,52 meg/l00g of soils; Ki in average varying between 2,06 and Fe2O3 free, varying between 11,20 and 12,64%. They have CEC dominantly influenced by the organic matter content of soil, that has a participation in average of 8I% of changes found in a horizon. They present cominantly Kaolinite and subdominance of Fe and Al oxides in mineral material, and variability o fCEC of mineral fraction, may be due to subdivision of clay particles and disturbance of structural units.

4) Method for determinning total organic and inorganic content in soils containing a high level of free iron, as occurs communly in Amazon soils. It was foliowed by MEHTA et alii method, with a modijication consisting in the elimination of cations through a changing resin strongly acid and the washing of the extracting column with 1% acetic acid solution, in order to separate the phosphorus retained by the resin particles and absorved in silica from the sample in the upper part of the column.

5) The objective of this study was determine the sources of agricultural production increase in Amazon Region during, 1975 to 1985. A modified technique of "shift-share" was used to quantify the sources of produclion increase by separating the analysis at State level for each crop. It was observed the annual increase of 9.4% in agriculture was attributed by variation in cultivated area. It was also noted that the locational component was second importam source of agricultural growth of region. The productivity and composition components had a little influence on variation in production.