L. I. Prochnow

Animal-based agriculture, phosphorus management and water quality in Brazil: options for the future

Eutrofizacao dos mananciais de agua se tornou uma preocupacao nos Estados Unidos, Europa e Australia. Na maioria dos casos, a eutrofizacao de mananciais de agua e acelerada pelo aumento na quantidade de fosforo adicionada, o que tem estreita relacao com o escorrimento superficial deste elemento, em funcao da intensificacao dos sistemas de producao de culturas e animais a partir do inicio dos anos noventa. Em virtude de pouca informacao com relacao aos impactos da agricultura na qualidade da agua, este artigo enfatiza modificacoes nos sistemas de producao de culturas e animais no Brasil no contexto das provaveis implicacoes quanto ao destino do fosforo no processo. Os dados apontam para um aumento de 33% no numero de animais (gado de corte, gado de leite, suino e frango) no periodo de 1993 - 2003, a maior parte deste aumento ocorrendo na regiao sul (Parana, Rio Grande do Sul e Santa Catarina), onde se localizam 43% e 49% da producao de suinos e frangos, respectivamente. Enquanto a producao de gado de corte se da predominantemente em sistema de pastejo a campo, com deposicao do esterco sobre os pastos, a producao de suino e frango ocorre em sistema intensivo de confinamento, o que resulta em elevadas quantidades de esterco em pequenas areas. Assim sendo, a discussao ira focalizar na producao de suinos e frangos. Tendo em vista o peso medio de suino (100 kg) e frango (1,3 kg), a producao diaria de esterco (4,90 e 0,055 kg por suino ou frango, respectivamente), e o conteudo medio de P no esterco (40 e 24 g kg-1 para suino e frango, respectivamente), estimou-se uma quantidade de 2,5 milhoes de toneladas de fosforo nos estercos de suino e frango, produzidas no Brasil em 2003. A maior parte foi produzida nas regioes sul e sudeste do Brasil (62% em conjunto), a qual representa apenas 18% da area do pais. No contexto da exigencia das culturas, os calculos apontam para 2,6 vezes mais fosforo produzido nos estercos (1,08 milhoes de toneladas) do que aplicado por meio de fertilizante (0,42 milhoes de toneladas) na regiao sul em 2003. Diante do fato que a quantidade utilizada por fertilizantes representa o necessario para atender as exigencias nutricionais das plantas, levando inclusive em consideracao o fosforo adsorvido pelo solo, se o esterco de suino e frango fosse considerado no sentido de substituir os fertilizantes aplicados, haveria uma sobra anual de 0,66 milhoes de toneladas apenas na regiao sul. Estas aproximacoes e estimativas claramente indicam que, como em outras partes do mundo, existe potencial para esta sobra anual de fosforo rapidamente acumular em certas regioes do Brasil. A menos que medidas sejam desenvolvidas e implementadas para utilizar este esterco, repetidas sobras anuais irao conduzir a um problema de dificil resolucao. Estas medidas podem ser agrupadas em dois tipos: as do manejo das fontes e as do transporte. As medidas que visam o manejo das fontes tendem a diminuir as quantidades de fosforo na dieta, usar aditivos no alimento, promover o tratamento e compostagem do esterco, bem como manejar com cuidado as doses, epoca, e metodo de aplicacao dos estercos. As medidas visando o manejo no transporte objetivam controlar a perda de fosforo no escorrimento do solo para os corpos de agua por meio da conservacao do solo e residuos, zonas vegetativas ribeirinhas de contencao, culturas de cobertura superficial, e pontes de aprisionamento ou areas alagadas. Estas medidas sao discutidas no contexto do clima, topografia, uso do solo, e ainda quanto ao sucesso dos programas de remediacao a serem implementados em fazendas ou bacias hidrograficas.

Controlling ammonia losses during manure composting with the addition of phosphogypsum and simple superphosphate

Com o proposito de avaliar a eficiencia do gesso agricola e do superfosfato simples em controlar as perdas de amonia por volatilizacao durante o processo de compostagem de estereos, foi conduzido um experimento em frascos de vidro fechados de 1,6 litro de capacidade, nos quais diferentes quantidades (50, 100, 150 e 200 kg.t-1) daqueles materiais foram misturadas com um substrato composto de uma mistura de partes iguais (em massa) de estereos frescos de galinha e de bovino. A amonia perdida por volatilizacao foi determinada apos 7, 14, 21, 28 e 35 dias, coletando-se o gas em solucao de acido sulfurico encerrada em pequeno recipiente o qual era, por sua vez, colocado no interior do frasco. O acido remanescente apos o periodo de exposicao a amonia era determinado por titulacao com solucao de NaOH 0,025N. A quantidade de amonia perdida do estereo por volatilizacao diminuiu com a adicao de ambos os materiais estudados, mas para todas as doses aplicadas o gesso agricola foi mais eficiente do que o superfosfato simples. Os decrescimos da volatilizacao foram tanto maiores quanto mais elevadas eram as doses de ambos os aditivos. Houve evidencias de que a reducao das perdas de amonia deveu-se a presenca do gesso nos materiais estudados.

Effectiveness of phosphate fertilizers of diffrent water solubilities in relation to soil phophorus adsorption

Phosphate fertilizers should match soil attributes to enhance agronomic effectiveness and recovery by plants. The purpose of this study was to test the agronomic effectiveness of P sources varying in water solubility on two soils differing widely in P adsorption capacity (PAC). Soils selected for the study were Oxisols with very low available P and presenting low and high PAC (Ox-LPAC and Ox-HPAC, respectively). Both were limed to pH 5.4 in a greenhouse study conducted utilizing corn as the test crop. Treatments consisted of the two soils interacting with five P sources (monocalcium phosphate - MCP, low-grade single superphosphate - LG-SSP, multimagnesium phosphate - MMP, Arad phosphate rock - PR and a P impurity in triple superphosphate - H14), and four rates of P (12.5, 25.0, 50.0 and 100.0 mg kg-1). A control with no P was added for each soil. The treatments were arranged as blocks with three replicates. Plants were harvested 45 d after germination. Dry-matter yield and P uptake were measured and the relative agronomic effectiveness (RAE) compared with MCP as the standard. When applied in low rates of P (12.5 and 25.0 mg kg-1) the RAE of the alternative sources was higher in the soil with high PAC (45, 66, 39 and 65% in the Ox-HPAC for the LG-SSP, MMP, PR and H14, respectively, as opposed to 24, 40, 14 and 47% in the Ox-LPAC). Results suggest that sources of P with low water solubility can be agronomically more effective in soils with high PAC.

Formas químicas, disponibilidade de manganês e produtividade de soja em solos sob semeadura direta

This field study had the following objectives: to determine the most appropriate micronutrient extractor to evaluate manganese bioavailability in soils under no-tillage; to evaluate the interaction of soil manganese with humic acids in soils under no-tillage with and without manganese deficiency through electronic paramagnetic resonance (EPR); and to evaluate manganese fractions (exchangeable, organic, oxides and residual) after manganese addition in soils under no-tillage with and without previous manganese deficiency for soybean. Four sites (I to IV) were selected to study the response curve to manganese (0 to 48 kg ha-1) fertilization in soybean. Sites I to III were located in Tibagi, state of Parana (PR), Brazil and site IV was in Castro (PR). Manganese rates affected the manganese concentrations in the soil, but not the manganese concentrations in leaves and the amount of manganese taken up by plants. Exchangeable, organic and oxide forms of manganese increased with the increasing rates applied at site I, with the largest increase being observed for the organic fraction (changed from 5.4 mg kg-1 manganese in the control to 35.1 mg kg-1 of manganese in the highest manganese dose). Manganese was not detected by EPR in the solid samples of humic acid - pH 3.0. Manganese quantification in the same samples after nitric-perchloric digestion, along clear signals of manganese detected by EPR in samples of humic acid - pH 2.4, indicated that manganese in the samples was strongly linked to the functional (probably carboxylic) groups of humic acid. The fact that there was no effect of manganese on soybean yield might be due to the complexation of the nutrient by soil organic matter. In general, DTPA-TEA was the most reliable manganese extractor to evaluate manganese availability to soybean under no-tillage.

Liming and electrochemical attributes of an oxisol under no tillage

No tillage areas are increasing in Brazil especially due to a general improvement in water and nutrient availability to plants. Few results have reported the effect of liming on soil electrochemical attributes in areas under the no tillage system. This study was conducted to evaluate the effect of liming (at the soil surface and incorporated to 0.2 m) on soil pH, point of zero salt effect (PZSE), electric potential, soil organic matter (SOM), and yield of soybean and corn, cultivated on an Typic Hapludox, submitted 12 years to no tillage. Rates of lime of 1/3, 2/3 and the total amount calculated for soil to reach a base saturation of 70 % (2.5 ton ha-1) were applied on soil surface. The full rate was also applied and incorporated to the 0.2 m depth. The effect of liming on PZSE was low due, most likely, to the low lime rates used in the experiment. SOM contents decreased as rates of applied lime increased, with the highest variation occurring between the control and the full rate of lime when incorporated. No clear effect of the lower values of SOM was observed in the PZSE values. The lack of interaction among lime rates and soil depth contributed for this situation, once the effect of SOM was diluted when considering the values of PZSE as the average for the soil layers (0-0.1; 0.1-0.2 and 0.2-0.3 m). There was no variation in the soil electric potential and in the yield of soybean and corn as a function of lime rates.

Evaluation of Rape Response to Different Sources of Phosphate Rock in an Alkaline Soil

A greenhouse experiment was conducted to evaluate the agronomic effectiveness of one unground, as received from Tunisia, and eight finely ground phosphate rock (PR) sources from Syria, Kazakhstan, Jordan, Russia, Mali, Burkina Faso, Tanzania, and China as compared with TSP for rape grown on an alkaline soil (pH 7.7). The P rates applied were 0, 5, 10, 25, and 50 mg P kg−1. The rape was grown to maturity. The yield of rapeseed obtained with each P source was fitted to a linear function with P rate. The relative agronomic effectiveness (RAE) of each PR with respect to TSP was calculated as the ratio of the slopes of the response function. The results show that RAE ranged from 0 to 88%, depending on the reactivity of PR. RAE correlated highly with the solubility of all PR sources as measured by 2% citric acid (CA) (R2=0.947) in a semi-log function. When the unground, highly reactive PR was excluded in the correlation, R2 was increased to 0.957 with 2% CA. The correlation was also very high (R2=0.963) when the RAE of the unground PR was plotted against its solubility measured in the finely ground form along with other finely ground PR sources. Low-reactivity PR with 2% CA-soluble P as low as 2.5% P can be 50% as effective as TSP in increasing yield of rapeseed even in alkaline soils. Use of indigenous PR sources, especially high reactive, for rapeseed production is feasible in those countries where agricultural soils are alkaline.

Variações induzidas de atributos químicos e sua influência na reflectância espectral de três solos do estado do Paraná

This study was conducted in order to verify the influence of induced chemical properties in standard kaolinite and samples of three soils from the State of Parana, Brazil - Hapludox Haplohumox and Tropohumults - on the spectral reflectance obtained in laboratory using a spectroradiometer, adjusted from 400 to 2500 nm. The samples were treated with solutions of calcium acetate, sodium acetate and incubated with calcium carbonate and sodium bicarbonate. Higher spectral reflectance was observed in the samples treated with calcium and sodium acetate induced by the higher concentrations of both ions. The incubation with calcium carbonate and sodium bicarbonate in the soil samples from the 40 to 60 cm layer promoted higher concentrations of calcium, sodium and effective CEC, lower amounts of organic matter and aluminum precipitation. These alterations contributed to higher reflectance along the wavelength range analyzed. Although changes were observed in the intensity of reflectance, the absorption features obtained in each case were the same. Statistical analysis showed the discrimination level of the spectral curves of soils and standard kaolinite.

Thermal treatment of aluminous phosphates of the crandallite group and its effect on phosphorus solubility

Optimization in the use of phosphate rocks is important and the residues of fertilizer production in the form of crandallite may be suitable for agronomic use after calcination. With the objective of evaluating the effect of thermal treatment of the aluminous phosphates of the crandallite group as related to solubility, crystalline structure and morphology, samples from the mine residues of three Brazilian phosphate deposits (Tapira-MG, Catalao-GO, and Juquia-SP) were collected, air-dried, and screened to 100 mesh. Sub samples were thermally treated at 300, 500, 700, and 900°C for 2 hours. Treated and untreated materials were analyzed by X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectrometry, and for the total and soluble P contents. The treatment of samples: (i) raised P solubility in neutral ammonium citrate solution, (ii) caused the disorganization of the crystalline structure of crandallite at 500°C and above, and (iii) altered their morphology (cracking and rounding). The increase in P solubility of samples after calcination indicates that the agronomic utilization of these marginal P sources may be of interest since plant growth may be favored due to higher P availability. New studies to evaluate these materials in order to determine their agronomic effectiveness must be carried out to establish adequate conditions that favor their use by plants.

Agronomic Evaluation of Calcined Crandallite from Three Brazilian Phosphate Deposits

Abstract Samples from the weathering mantle containing crandallite of three Brazilian phosphate deposits, Tapira, Catalão, and Juquiá, were characterized, calcined, and agronomically evaluated. The calcination process increased total phosphorus (P) and neutral ammonium citrate soluble (NAC) P contents of all samples. The NAC solubility of original Tapira, Catalão, and Juquiá was about 5% of total P, whereas for calcined samples it was 54, 16, and 53%, respectively. In a greenhouse study, rates of P were applied at 0, 10, 20, 40, 80, and 120 mg P kg−1 from the calcined materials and MCP (monocalcium phosphate) to an Ultisol cropped with upland and flooded rice for 65 days. The results showed that the calcined P samples increased dry‐matter yield and P uptake with increasing rates of P applied for both crops. Tapira and Juquiá were more effective for flooded than for upland rice. The calculated values of relative agronomic effectiveness of Tapira, Catalão, and Juquiá with respect to MCP were 57, 48, and 53% in dry‐matter yield for upland rice and 64, 50, and 69% for flooded rice, respectively.

Agronomic Effectiveness of Cationic Phosphate Impurities Present in Superphosphate Fertilizers as Affected by Soil pH

Abstract The general concept that low‐water‐soluble phosphorus (P) fertilizers should be more agronomically effective when applied to acidic soils was developed based on sources containing mainly calcium (Ca)‐P compounds, but it may not hold true for sources with different chemical composition. To obtain information related to this issue, two important iron (Fe)–potassium (K)–P compounds present in superphosphates [Fe3KH8(PO4)6 · 6H2O, H8, and Fe3KH14(PO4)8 · 4H2O, H14] were prepared and characterized. These P sources were used to provide 30 and 60 mg P kg−1 as neutral ammonium citrate (NAC)+H2O‐soluble P. Reagent‐grade monocalcium phosphate (MCP) was used as a standard P source with high water solubility with an additional rate of 120 mg P kg−1 included. Also, mixtures of both Fe‐K‐P compounds and MCP were prepared to provide 0, 25, 50, 75, and 100% of the total P as MCP. All sources were applied to a clayey loamy acid soil (pH 5.3) classified as Rhodic Kanhapludult. The soil was incubated at two rates (0 and 10 g kg−1) of lime, which resulted in pH 5.4 and 6.8. Upland rice was cultivated to maturity. The H14 compound confirmed to be a highly effective source of P for the rice plants at both soil pH, as opposed to the H8, which was poorly effective when applied alone. When mixed with water‐soluble P (WSP), the H8 was able to provide P to the plants with the maximum yield of upland rice reached with 54.8 and 80.5% of WSP for pH 5.4 and 6.8, respectively. The high agronomic performance of the H14 compound clearly indicates that this low‐water‐soluble P source cannot be deemed as ineffective at high soil pH. Conducted with the financial support from the Research Foundation for the State of São Paulo (FAPESP).