Antonio Nolla

Atividade e especiação química na solução afetadas pela adição de fósforo em latossolo sob plantio direto em diferentes condições de acidez

In no-tillage systems, crop residues and nutrients, namely phosphorus and calcium, accumulate in soil surface and can inactivate soil aluminum. In this way, only the presence of this element in soil analysis does not indicate plant toxicity, since organic and inorganic anions may affect the free aluminum dynamics by decreasing its activity in the soil solution. Knowledge on ion activity and speciation in soil solution is therefore useful to understand Al dynamics. Ionic activity and speciation were determined in the soil solution of an Oxisol (Rhodic Hapludox), under no-tillage for the seven preceding years and different acidity conditions due to previous applications of variable lime rates in 1994. After the chemical characterization of the study soil, undisturbed samples were collected in PVC columns and subjected to surface application of different phosphorus rates (0, 40, 80, 160, 320, 640, 1.280, and 2.560 mg L-1 of P in solution) and then incubated for 30 days. Soil solution was directly extracted from the tubes by centrifugation and acidity attributes and cations and anions were determined to estimate ionic activity and speciation using a Visual Minteq A2 program. A decrease in aluminum content and activity in soil solution after phosphorus application was observed. The increase of phosphorus in soil solution did not directly affect aluminum inactivation, because no aluminum phosphates were formed. The increase of phosphorus in soil solution, however, displaced organic and inorganic anions that were effective in aluminum complexation in soil solution.

Potencial de recuperação física de um latossolo vermelho, sob pastagem degradada, influenciado pela aplicação de cama de frango

A criacao intensiva de frango gera uma grande quantidade de residuos ricos em nutrientes cujo uso agricola pode ser viabilizado pelos produtores, na adubacao das culturas comerciais. Objetivou-se avaliar a influencia da fertilizacao com cama de frango na recuperacao fisica de um Latossolo. O experimento foi instalado em um Latossolo Vermelho Distrofico tipico, textura media, sob pastagem degradada de Brachiaria decumbens Stapf. Os tratamentos estudados foram: 0, 1.200, 2.400, 4.800 kg ha-1 de cama-frango e 2.400 kg ha-1 de cama-frango + adubacao mineral com 36 kg ha-1 N, 60 kg ha-1 K2O e 60 kg ha-1 de P2O5. As aplicacoes foram realizadas em janeiro de 2004 e o solo amostrado em duas epocas distintas (60 e 210 dias apos aplicacao), nas profundidades de 0-20 e 20-40 cm, para a caracterizacao dos atributos fisicos: argila dispersa em agua, grau de floculacao, densidade do solo e porosidade total. O teor de argila dispersa em agua decresceu com o aumento das doses de cama aplicadas e, consequentemente, houve um incremento no grau de floculacao; houve uma pequena reducao na densidade do solo e na porosidade total. Os atributos fisicos do solo avaliados responderam com maior intensidade as aplicacoes de cama de frango nas doses variando de 2.666 a 3.750 kg ha-1.

Monitoring and evaluation of need for nitrogen fertilizer topdressing for maize leaf chlorophyll readings and the relationship with grain yield

The study was carried out for two years in maize in succession to the wheat using no tillage system in a distroferric Red Latosol (Hapludox). Methods of management nitrogen fertilizer (120 kg ha-1) with ammonium sulphate were studied; the fertilizer was applied in maize sowing or in maize topdressing, and N with previous application in wheat sowing. In addition, leaf chlorophyll reading was used as an indicator for the need for topdressed nitrogen fertilizer. Nitrogen supply index (NSI) was shown to be effective at predicting need for topdressed nitrogen fertilizer for maize. The application of N improved the yield of the maize independent of the management system. The flowering stage was carried out at the appropriate time in order to estimate the nitrogen nutrition state and yield of maize using the relative chlorophyll level (RIC).