O objetivo deste trabalho foi avaliar a qualidade de um Latossolo Vermelho submetido a sistemas de cultivo com preparo convencional e plantio direto. Foram estudadas duas áreas experimentais, localizadas na Embrapa Cerrados, em Planaltina, DF, com oito e dez anos de cultivo. Foram coletadas amostras de solo, em diversas profundidades, nas parcelas experimentais e em área de cerrado nativo. Os seguintes atributos foram avaliados: densidade do solo, porosidade total, capacidade de água disponível, grau de floculação, resistência do solo à penetração, teor de matéria orgânica, capacidade de troca catiônica, fósforo remanescente, carbono da biomassa microbiana e respiração basal. Os dados obtidos foram comparados a valores referenciais quanto à qualidade do solo, mediante modelagem gráfica. Observou-se que a qualidade do solo, em ambos os sistemas de cultivo, é similar quanto aos atributos físicos; os teores de matéria orgânica e fósforo remanescente também são semelhantes, mas a capacidade de troca catiônica é mais alta no solo sob plantio direto. Em relação aos atributos biológicos, o solo sob plantio direto apresenta atividade biológica mais elevada. A qualidade do solo em ambos os sistemas é similar, em relação aos atributos avaliados.
Abstract. Let K be a field and let N = {1, 2, . . . }. Let Rn = K[xij | 1 ≤ i ≤ n, j ∈ N] be the ring of polynomials in xij (1 ≤ i ≤ n, j ∈ N) over K. Let Sn = Sym({1, 2, . . . , n}) and Sym(N) be the groups of the permutations of the sets {1, 2, . . . , n} and N, respectively. Then Sn and Sym(N) act on Rn in a natural way: τ (xij) = x τ (i)j and σ(xij) = x iσ(j) for all τ ∈ Sn and σ ∈ Sym(N). Let Rn be the subalgebra of the symmetric polynomials in Rn,In 1992 the second author proved that if char(K) = 0 or char(K) = p > n then every Sym(N)-invariant ideal in Rn is finitely generated (as such). In this note we prove that this is not the case if char(K) = p ≤ n.We also survey some results about Sym(N)-invariant ideals in polynomial algebras and some related results.
This work aimed to perform financial analysis in an agroforestry system, in the Federal District - Brazil, with trees barriers and polyculture of crops, from 2015 to 2017. Summer polyculture involved rice (Oryza sativa), beans (Phaseolus vulgaris) and corn (Zea mays) while winter polyculture consisted of tomato (Solanum lycopersicum), cabbage (Brassica oleracea var. capitata) and beetroot (Beta vulgaris). Financial evaluation was based on Net Present Value, Periodic Equivalent Benefit, Payback and Internal Rate of Return. It proved to be feasible technically and economically, presenting IRR of 9.52% and payback of 22 months for the organic system. Profitability was higher considering the prices for organics in the Market of Brasilia. Conventional system showed a payback period of 34 months, 35% higher than the payback for an organic system. This result serves as stimulus to the adoption of organic cultivation systems. As an unconventional investment project, this information serves as subsidies for government policies.
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