Nelson Machado da Silva

Comparação de quatro extratores de fósforo de solos

A comparative study of four methods used for the extraction of soil phosphorus, is presented. The methods were: a) IAC method, based on the extraction of, 5cm3 of soil with 50ml of 0.05N H2SO4; b) a modified Bray I method, based on the extraction of 2.5cm3 of soil with 50m1 of a solution 0.03N in NH4F and 0.025N in HCl; c) Olsens method, based on the extraction of 2.5cm3 of soil with 50ml of 0.5N NaHCO3 solution at pH 8.5; d) an anion exchange resin method based on the extraction of 5cm3 of soil with 2.5cm3 of an anion exchange resin contained in a polyester netting bag, by shaking in 50ml water. For each method, the correlation coefficients between soil phosphorus and the response to phosphorus fertilization of 16 field experiments of cotton and 16 field experiments of corn were, respectively, 0.683, 0.650, 0.391 and 0.802, indicating the superiority of the anion-exchange resin method for the assessment of soil phosphorus availability.

Exchangeable aluminum and base saturation as criteria for lime requirement

O criterio do aluminio para determinar a necessidade de calagem de solos, vem sendo usado ha dezesseis anos no Brasil. As quantidades de calcario indicadas sao em geral baixas. Neste trabalho, procurou-se avaliar esse metodo, com base em resultados de ensaios de calagem, realizados em tres locais e durante varios anos. Em Mococa, em podzolico vermelho-amarelo, foram considerados cinco plantios de milho, um de algodao e um de soja; em Sao Simao, em latossolo vermelho-escuro textura media, tres plantios de soja; em Guaira, em latossolo roxo, tres plantios de algodao. Em todos os casos, a producao continuava a aumentar, com a elevacao das doses de calcario, mesmo em niveis de calagem superiores aqueles suficientes para praticamente neutralizar o aluminio. Mostrou-se que o criterio do aluminio nao e adequado, do ponto de vista quantitativo, para calculos de calagem. O criterio da saturacao em bases apresentou-se como alternativa adequada, para esse fim, relacionando bem com as respostas das culturas, alem de ser muito flexivel, de facil utilizacao, e apresentar fundamento teorico adequado. Em geral, a producao maxima nao foi atingida nos ensaios, mas estimou-se que ela seria obtida com valores de saturacao em bases acima de 60%.

Modos de aplicação de regulador vegetal no algodoeiro, cultivar IAC-22, em diferentes densidades populacionais e níveis de nitrogênio em cobertura

ABSTRACT TYPES OF GROWTH REGULATOR APPLICATION, PLANTING DENSITIES ANDNITROGEN LEVELS FOR THE COTTON CULTIVAR IAC 22. The present work was developed during the growing seasons of 1996/97, 1997/98, 1998/99 and1999/00 at Ribeirao Preto, Tiete, Guaira, Campinas and Ilha Solteira, State of Sao Paulo, Brazil. Theexperimental design was the completely casualized blocks, using the factorial arrangement with twelvetreatments (3 x 2 x 2) and four replications. The objective of this work was to study plant density (6; 10and 14 plants/m); nitrogen levels at broadcasting (40 and 60 kg.ha -1 of N/ha) and types of growthregulator application (single application at flowering or splitting in four times, since the thinning). Thesplit application conduced to lower height of plants and greater weight of bolls when compared to thesingle application of the growth regulator. The application of the highest level of N, increased theleaves nitrogen content in and cotton yield, and reduced the lint percentage. increasing plant densityfrom 6 to 10 and 14 plants/m, reduced lint porcentage and bolls weight.

EFEITOS DO CALCÁRIO E DO GESSO NAS CARACTERÍSTICAS QUÍMICAS DO SOLO E NA CULTURA DO ALGODÃO

Field trials with cotton cultivar IAC-20 were conducted during four years on an acid distrophic Dusky Red Latosol from Guaira, State of Sao Paulo, Brazil. The experiments and the treatments were randomized complete blocks with split-plots, with 0.6, 1.8 and 3.0 t/ha of limestone in the plots and 0, 2, 4 and 6 t/ha of phosphogypsum in the subplots incorporated in the soil in the first year and reapplied after two years. The results of successive soil analysis indicated that the action of limestone was more evident in the plow layer, whereas gypsum was more effective in the subsoil at a 40-60 cm depth, due to leaching of bases through the soil profile promoted by sulphate ion. The increase of leaf contents of S, Ca and Mg promoted by the phosphogypsum was considered also good as a evidence of enhanced root development in the subsoil of these treatments. The residual effect of both limestone and gypsum was low after the first application, but considerably higher after reapplication, especially for limestone. Along the time, the use of gypsum caused a decrease of Mg and especially K leaf contents.

Ensaio de longa duração com calcário e cloreto de potássio na cultura do algodoeiro

Decorridos cinco anos de um ensaio de calagem e adubacao potassica do algodoeiro, em latossolo roxo distrofico do municipio de Guaira (SP), reaplicou-se o calcario nas mesmas doses da primeira fase (0, 2, 4 e 6 t/ha). Utilizou-se o calcario dolomitico com 25,3% de CaO, 19,9% de MgO e 68% de PRNT. O potassio foi aplicado em subparcelas nas doses anuais de 0, 50, 100 e 150 kg/ha de K2O, na forma de cloreto de potassio. Fez-se, anualmente, a adubacao com N, P2O5 e B nas doses respectivas de 60, 100 e 1,5 kg/ha. O efeito da calagem no aumento dos valores de pH e da saturacao por bases da camada aravel do solo foi imediato, havendo, no entanto, um decrescimo nos valores desses indices apos o segundo ano e um retorno aos niveis da fase anterior. Concomitantemente, a lixiviacao de Ca e de Mg foi acentuada a partir do segundo ano apos a reaplicacao do calcario. O efeito do potassio na producao de algodao foi mais evidente com a calagem. Sintomas de sua deficiencia foram observados nas plantas das parcelas com calcario e sem adubacao potassica. Na ausencia de calagem, a dose maxima de potassio provocou injuria nas plantas. O indice de 90% da produtividade maxima esperada foi alcancado em presenca da adubacao potassica e quando a saturacao por bases aumentou ate 60% na camada aravel e 40% nas profundidades de 20-40 cm e 40-60 cm.

Dez anos de sucessivas adubações com boro no algodoeiro

A long term trial of boron fertilization was conducted with cotton in a latin square design, firstly installed in 1983 on a low fertility Dusky Red Latosol, limed and frequently fertilized without boron. Rates of 0, 0.2, 0.4, 0.8, 1.6 and 3.2 kg/ha of B as borax (11% of B), were applied annually at planting time. The cotton variety used was the IAC-20. The plots were limed in the fourth, sixth and nineth years. In the seventh year Canajus indicus was cultivated, in crop rotation, to control the increasing incidence of nemathodes. After the eighth year, there was intense attack of Anthonomus grandis Boheman. Thus, cotton yield diminished from the first period, of three years, to the last, while the effect of boron accumulation increased in this sense. In the first period, there was an enchance of yield at rate of 0.4 kg/ha of B, but after lime reaction the best responses were obtained with 0.8 kg/ha of B. The plants were more sensitives to fertilization in terms of boron concentration in the leaf blade, specially after liming. Rates of 1.6 and 3.2 kg/ha of B were injurious starting from the beginning of the study. After liming, yield decreases were related with B concentration higher than 50 mg/kg in leaf blades. Results of soil analysis in the nineth year, indicated a great residual effect of boron accumulation in the 0-20 cm soil layer, as well as leaching of the micronutrient at least down to 40-60 cm deep, in proportion to the rates applied.

Efeitos do boro em algodoeiro cultivado em condições de casa de vegetação

Visando obter subsidios para a instalacao de futuros ensaios de campo com adubacao boratada do algodoeiro, foi conduzido estudo em casa de vegetacao, utilizando-se solo comprovadamente carente em boro para essa cultura. Foram usadas doses de 0, 133, 266 e 532mg de borax por vaso contendo 5,0kg de terra. Em vasos extras, estudaram-se niveis mais elevados do produto. O efeito de boro sobre a altura media das plantas, peso de capulho, peso de sementes e comprimento de fibra foi significativo estatisticamente e de natureza quadratica. A concentracao de B na materia seca da parte aerea da planta ou da folha cresceu em proporcao a dose utilizada. No caso da analise de folhas de plantas carentes, a concentracao variou de 10 a 39ppm, com media de 19pmm de B, enquanto em plantas com grave sintoma de toxicidade foi obtido indice superior a 590ppm de B. Em plantas com carencia de boro foi observado um ou varios dos seguintes sintomas: paralisacao de crescimento, superbrotamento, intumescimento de nos com escurecimento de tecido, deformacoes do limbo e do peciolo de cotiledones e de folhas verdadeiras, aneis concentricos com necroses correspondentes da medula de peciolos foliares e deformacoes das flores. Como sintoma de toxicidade, observou-se clorose marginal e internerval do cotiledone e/ou da folha verdadeira, que evoluiu ou nao para necrose do tecido, permanecendo as nervuras com coloracao verde normal.

Modo e época de aplicação de fosfatos na produção e outras características do algodoeiro

The traditional mode of phosphate application to cotton was compared with broadcasting application in a long term trial conducted on a DusKy Red Latosol, with a low level of phosphorus. Triple superphosphate was applied annualy (121 kg/ha of P2O5)in furrows at sowing, during six years, or broadcasted and incorporated, through one application (728kg/ha of P2O5) in the first year, or two applications in the first and fourth years (364kg/ha, at each time). A thermal phosphate (18% P2O5) was also tested in two broadcasting applications. All treatments were compared to a control, with constant doses of N and K, but without P. During the six years of phosphate fertilization, higher yields of IAC 18 cotton variety were obtained, with annual application at sowing time, except for the first year due to the low initial disponibility of P. High quantities of broadcasted phosphate led to visual potassium deficiency symptoms, with losses in yield, Micronaire index and maturity of fibers. Therefore, due to the good yield performance obtained with a moderate dose of phosphate, in the years of application, it was suggested that a combination between broadcast and localized application should be studied, in future experiments. Other characteristics of cotton such as boll and seed weight plus fiber length, also increased significantly with P fertilization. The residual effect of the traditional mode of phosphate application, studied during the last three years, with IAC 20 cotton variety, showed significant results only for yield.

A calagem na reação do algodoeiro a adubação com superfosfato simples

Apos o quarto ano de conducao de um ensaio permanente de calagem e de adubacao mineral com o algodoeiro, iniciado em 1974 em um latossolo roxo acido, argiloso (66%) e rico em materia orgânica (4,1%), no municipio de Guaira, SP, reaplicou-se o calcario. Utilizaram-se as mesmas doses da primeira fase (1,5, 3,0 e 6,0 t/ha), exceto nas parcelas testemunhas, onde se fez uma calagem minima com 1,5 t/ha. A adubacao mineral teve continuidade com aplicacoes anuais de 60 kg/ha de N (sulfato de amonio) e P x K, em esquema fatorial, nas doses de 0, 60 e 120 kg/ha de P2O5 (superfosfato simples) e 40 e 80 kg/ha de K2O (cloreto de potassio). Por falta de resposta significativa do algodoeiro a potassio, nao se considerou o efeito do referido nutriente. No tratamento com a dose maxima de calcario, foi possivel estabilizar o pH em H2O na camada aravel do solo, ao redor de 6,0 e, em funcao da lixiviacao de bases (Ca + Mg), na faixa de 5,5 na camada subsuperficial, que representariam condicoes adequadas para o desenvolvimento da cultura em apreco. O indice pH, os valores de Ca e de Mg da analise de terra e a produtividade das plantas cresceram significativamente com a reaplicacao do calcario. A resposta do algodoeiro a aplicacao acumulada de superfosfato simples diminuiu com a correcao da acidez do solo, configurando tipica interacao negativa entre a adubacao fosfatada e a calagem. O metodo da resina trocadora de ânions mostrou-se mais adequado na extracao do fosforo do solo do que o do acido sulfurico diluido, tendo em vista nao so a boa repetitividade dos resultados analiticos observada durante os quatro anos de estudos como tambem a estreita correlacao obtida entre os teores de P-resina e os valores do indice pH da analise de terra. Decrescimos significativos na concentracao de macronutrientes e de micronutrientes do limbo foliar do algodoeiro, devidos a calagem e a adubacao fosfatada, confirmam a necessidade de se prevenir contra provaveis problemas que possam ocorrer, representados especialmente por deficiencias de K e B, na correcao de solos acidos e de baixa fertilidade.

Estudo do parcelamento da adubação potássica do algodoeiro

The advantage of split application of potassium chloride in cotton was studied in ten field experiments, conducted at different localities during the period of 1975 to 1981. In such cases, doses of 0, 60 and 120kg/ha of K2O, were placed in a fillet beside and below the seeds, at planting. In other treatments 1/3. 1/2, 2/3 or the total quantity of the highest level of potassium fertilizer was applied together with nitrogen, just after thinning, in a side-dressing operation, and covered slightly by subsequent cultivation. When all the K was applied at planting, linear effect on cotton yield appeared only in 10% of the experiments. This proportion increases to 40% when split applications were made. However, in combined analysis of all tests no significant difference was found between the two methods. Based in a study of simple correlations between cotton productivity and potassium application, expressed as the control treatments relative yield and indices of soil analysis ike 1/K+ and (Ca2+ + Mg2+)/K+, three groups of experiments were established, according to different expected responses. Considering the group of high expected responses [K 43], parcelled application resulted in increases of cotton yield when compared with the normal method of application. Similar tendency was observed in the group of intermediate expected responses [0.8-0.24 meq of K+ and 20-43 of (Ca2+ + Mg2+)/K+]. In potassium deficient soils split application of potassium chloride can be recommended, 1/2 or 2/3 of the total level furnished at planting and the remainder just after thinning, by side-dressing, mixed with nitrogenous fertilizer and followed by cultivation.