Avaliação da fertilidade do solo em diferentes sistemas de uso da terra em área de várzea na Amazônia Central

Abstract

Thestudy was made in high and low floodplain soils ofthe river Solimões/Amazonas,in the municipal districts of Careiro da Várzea, Manacapuru, Silves, Iranduba, and Itacoatiara. In each site were identified and selected different land use systems where samples in the layers 0-10, 10-20 and 20-40 cm deep were collected. In the high floodplains, one primary forest, pasture and secondary forest areas; and three farm and four vegetable garden areas were sampled.In thelow floodplains,one pasture,two secondary forestand six vegetable garden areas were also sampled. The objectives were to evaluate the distribution of chemical attributes in the soil profile and to compare the different systems ofland use both in the high and low floodplains. The determinations made were: Ca,Mg,K,P,C,N,pH,Al,Cu,Mn, Zn,and Fe.The entirely casualized delineation wasadopted,inafactorialarrangementofthe type 10 X 3(high floodplains)and 9 x 3(low floodplains), corresponding to the land use systems and profile depth,with 30and 27treatments,respectively,and in the 3 repetitions. Thecomparisonsamongaverageswere madeaccordingto Tukey.Inthehighfloodplains,the distributionofchemicalattributesinthe profile(K,P,Mg,pH,Al,Fe,Mn,C,N,Zn,Cu),in the layers 0-10, 10-20 and 20-40 cm, presents little variation, except for the calcium, which had a higher concentration in the superficial layer of the soil. In the low floodplains, the annual flood cycles were significantly related to the distribution of nutrients within the profile, and. Ca,Mg,K,Cu,and Zn increased with the depth,and also occurring an elevation on the acidity ofthe soil and on the Ap""content. For C,N and P,however,a reverse pattem wasfound,and these are more availableonthe soilsurface.ItwasshownthatFeand Mnare irregularly distributed in the profile. In the high floodplains, macro and micronutrients appear in high concentrations,and the forest stands out as a system that preserves the leveis ofC,N, O Mg,Cu,Zn,Mn and Fe.There are significant variations between vegetable garden and farm areas regarding nutrient contents. The forest maintains high leveis of fertility, with high acidity and presence of aP"^. In the low floodplains, there is also high fertility, including Ca, Mg,P,K,Cu,Zn, Fe, and Mn,but in most systems, differences in the nutrient availability among different vegetable gardens and among different secondary forests. In the greatest part ofland use systems,the leveis ofC and N were low, confirming that N is one ofthe main limiting factors for agricultural production the a floodplain area in Amazônia. For the sum of bases of soils ofthe high and low floodplains, it was verified that the Ca had predominance over the other macronutrient cations, and among the micronutrients Fe was the most abundant elemen