RESUMO Adubações com fósforo (P) apresentam baixa eficiência devido à adsorção de P na superfície da argila em solos tropicais. O superfosfato complexado com ácido húmico (SSP+HA) é apresentado como uma alternativa para melhorar a eficiência do uso do P e a produtividade das culturas. Nesse sentido, o objetivo deste estudo foi investigar o desempenho do SSP+HA na produção de cana-de-açúcar com incrementos da matéria seca (MS) e conteúdo de P nas plantas. O experimento foi conduzido com duas fontes de P (superfosfato simples-SSP; SSP+HA) e cinco doses (0; 45; 90; 135 e 180 kg ha-1 de P2O5). A dose de 135 kg ha-1 foi usada para explicar o efeito residual do P, coletando solo na cana-planta e primeiro corte. Amostras de caules, ponteiras e raízes foram coletadas para determinar MS e conteúdo de P; ambas variáveis foram usadas para calcular a eficiência de assimilação de fósforo (EaP). Os resultados mostraram que a aplicação de SSP aumentou MS e conteúdo de P nas plantas, com desempenho superior ao SSP+HA. A EaP foi maior no SSP+HA, indicando que o P foi metabolizado de forma mais eficiente, mas não refletiu no aumento de MS. As doses de P aumentaram a produtividade da cana-planta, mas não houve efeito do P aplicado em soqueira, devido ao efeito residual do P aplicado no plantio. O SSP apresentou desempenho superior ao SSP+SH no plantio da cana-de-açúcar. Mais pesquisas são necessárias para melhor ilustrar o efeito do SSP+HA na absorção e translocação do P.

ABSTRACT In tropical soils, the efficiency of phosphorus (P) fertilization is low, due to P adsorption on the surface of the clay. Superphosphate complexed with humic acid (SSP+HA) is presented as an alternative for improving P use efficiency and crop yields. The aim of this study was to investigate SSP+HA performance in sugarcane production including increases in plant dry matter (DM) and P content. The experiment was conducted with two sources of P (simple superphosphate - SSP, SSP+HA) and five doses (0, 45, 90, 135 and 180 kg ha-1 P2O5). The dose of 135 kg ha-1 P2O5 was used to explain the residual effect of P, collecting soil samples from the plant cane and first ratoon. Stalk, top and root samples were collected to determine DM and P content; both variables were used to calculate the P assimilation efficiency (PaE). Results showed that the application of SSP increased the DM and P content of the plants, with superior performance compared to SSP+HA. PaE was greater under SSP+HA, indicating that P was metabolized more efficiently; however this did not reflect in an increase in DM. AThe P rates increased the sugarcane yield in cane plant, but there was no effect of P applied in the first ratoon due to the residual effect of P applied in planting. SSP presented superior performance compared to SSP + SH in sugarcane planting. Further research is needed to better demonstrate the effect of SSP+HA on the absorption and translocation of P.

ABSTRACT: Integrating plant density and nitrogen (N) management is a strategy for improving corn yields, especially for off-season corn production in the tropics. This study tested the hypothesis that increasing plant densities and N rates promotes yield gains for off-season corn production in high-yielding environments. The aim of the study was to investigate the yield performances of two hybrid versions (DKB PRO and DKB PRO3) submitted to three plant densities (55,000; 65,000 and 75,000 plants ha−1) and four N rates (control, 60, 120 and 180 kg ha−1 N). Field trials were undertaken at Uberlândia-MG (site1 and 2) and Pedro Afonso-TO (site 3), Brazil from which data on corn yield parameters were collected and analyzed. Multivariate analysis separated the three trial areas into two groups, presenting high (sites 1 and 2) and low yields (site 3), which were related to weather conditions. There was no influence of a hybrid version or plant densities on crop yields at site 1 or 2. In contrast, there was a positive response to increasing plant densities and the use of DKB PRO3 at site 3. A significant response to N was observed at sites 2 and 3, following a plateau model. Our results suggest that N application rates and plant densities do have the potential to increase off-season corn yields in low yielding environments.

ABSTRACT: Determining nutrient uptake and accumulation rates by cotton crops is important to define management strategies, especially for transgenic varieties, which are cultivated using high-technology approaches that require substantial investment to maximize yield. Currently in Brazil, the states of Bahia and Mato Grosso are responsible for 84.4 % of the total cotton growing area. In the present study, two trials were conducted in 2013, one that involved planting FM 940 GLT, FM 980 GLT, and FM 913 GLT varieties in the state of Bahia and the other which involved FM 940 GLT and FM 980 GLT varieties in the state of Mato Grosso. The aim of the two trials was to represent the two regions that currently encompass the largest areas of cotton cultivation. Tissue samples, consisting of leaves, stems, and reproductive components, were collected eleven times during the crop cycle for determination of nutrient content and shoot dry matter. After weighing, plant tissue samples were dried and ground to determine nutrient contents. Because there were no overall differences in nutrient contents and biomass accumulation of the varieties during the crop cycle, we undertook joint analysis of the data from all varieties at each site. Favorable climatic conditions in Bahia promoted plant biomass production that was twice as much as plants grown in Mato Grosso, with cotton yields of 6.2 and 3.8 t ha−1 of lint and seed, respectively. The maximum nutrient accumulation occurred between 137-150 days after emergence (DAE) for N; 143-148 for P; 172-185 for K; 100 for Ca; 144-149 for Mg; and 153-158 for S. Maximum uptake ranged from 218-362 kg ha−1 N; 26-53 kg ha−1 P; 233-506 kg ha−1 K; 91-202 kg ha−1 Ca; 28-44 kg ha−1 Mg; and 19-61 kg ha−1 S. On average, the sites revealed nutrient export of 14, 2, 23, 3, 2, and 2 kg t−1 of lint and seed for N, P, K, Ca, Mg, and S, respectively, with little variation among sites. Extraction of nutrients per area by cotton vary among sites, but nutritional requirement of cotton per unit of lint and seeds is similar independently of yield potential.

Resumo: O objetivo deste trabalho foi avaliar o efeito da aplicação foliar de magnésio no desempenho produtivo de soja (Glycine max) e milho (Zea mays) em solo com níveis adequados de saturação por base e conteúdo de magnésio, no Brasil. Os experimentos foram desenvolvidos em Latossolo Vermelho-Amarelo distrófico cultivado com soja e milho nas safras 2013/14 e 2014/15, respectivamente. Os tratamentos consistiram de aplicação foliar de doses de Mg (50, 100, 250, 500, 1.000 e 1.500 g ha-1 e controle sem Mg) nos estádios fenológicos V4, R1 e R5.1 (soja) ou V4 e R2 (milho), na forma de sulfato de magnésio heptahidratado (MgSO4∙7H2O). Avaliaram-se o índice SPAD, teor foliar de Mg, produtividade de grãos e massa de 100 grãos. A aplicação foliar de Mg aumentou o índice SPAD na cultura da soja e o teor foliar de Mg na cultura do milho. As doses de Mg de 540 e 890 g ha-1 proporcionaram incrementos de 325 e 737 kg ha-1 na produtividade da soja e do milho, respectivamente, independentemente do estádio fenológico. A aplicação foliar de Mg no estádio reprodutivo aumentou em 2% a massa de 100 grãos de ambas culturas. A pulverização foliar de Mg melhora os parâmetros produtivos das culturas de soja e milho.

Abstract: The objective of this work was to evaluate the effect of magnesium foliar spray on yield performance of soybean (Glycine max) and corn (Zea mays) cultivated in soil with adequate levels of base saturation and magnesium content in Brazil. The field trials were conducted on a Typic Hapludox cultivated with soybean and corn in the 2013/2014 and 2014/2015 crop seasons, respectively. Treatments consisted of Mg rates (50, 100, 250, 500, 1,000 and 1,500 g ha-1 and a control without Mg) applied during the V4, R1, and R5.1 (soybean) or V4 and R2 (corn) phenological growth stages as magnesium sulfate heptahydrate (MgSO4∙7H2O). The SPAD index, leaf Mg content, grain yield, and 100-grain weight were evaluated. The Mg foliar spray increased the SPAD index in soybean and the leaf Mg content in corn. The Mg rates of 540 and 890 g ha-1 increased in 325 and 737 kg ha-1 the yield performance of soybean and corn, respectively, regardless of the phenological growth stages. The Mg application during the reproductive stages increased in 2% the 100-grain weight for both crops. Foliar spraying of Mg improves the yield performance in soybean and corn crops.

RESUMO A manutenção da palha na superfície do solo dificulta a incorporação mecânica dos fertilizantes nitrogenados no solo. A aplicação de ureia na superfície nestas condições favorece as perdas de N-NH3 por volatilização, tornando necessário o uso de inibidores de urease ou fontes menos sujeitas à volatilização. Avaliou-se a volatilização de NH3 de fontes de N aplicadas sobre palhada de cana-de-açúcar. O experimento foi realizado em Nitossolo Vermelho eutrófico no município de Iracemápolis-SP em junho de 2014. O delineamento experimental foi em blocos aleatorizados, com sete tratamentos e quatro repetições. Os tratamentos foram controle [CO], nitrato de amônio [NA], NS30TM (fusão entre nitrato de amônio-75% e sulfato de amônio-25%) [NS30TM], mistura física de sulfato de amônio (75%) e nitrato de amônio (25%) [NA-SA], ureia [UR], ureia recoberta com 0,4% Cu e 0,15% B [UR-CuB] e ureia tratada com 530 mg NBPT kg-1 [UR-NBPT]. Todos os tratamentos (exceto controle) foram aplicados na dose de 100 kg ha-1 de N. As perdas de N-NH3 foram avaliadas até 30 dias após adubação (DAA). As máximas perdas de N-NH3 ocorreram aos 16 DAA para UR e UR-CuB e aos 20 DAA para UR-NBPT. As perdas acumuladas de N-NH3 foram 20, 17 e 14% para UR, UR-CuB e UR-NBPT, respectivamente; para as fontes não amídicas as perdas foram inferiores a 1% do N aplicado. A adição de inibidores de urease tem potencial em reduzir perdas por volatilização da ureia mesmo em condições de elevada quantidade de palha sobre o solo.

ABSTRACT Maintenance of crop residues over soil surface under conservational systems limits incorporation of nitrogen fertilizers into the soil. Application of urea over crop residues enhance N-NH3 volatilization losses, justifying the usage of urease inhibitors or N sources less susceptible to volatilization under such conditions. This study aimed to evaluate volatilization losses from N sources applied over sugarcane straw. A field trial was carried out in a sugarcane field in Iracemapolis, Sao Paulo on a Typic Kandiudox in June 2014. We used a complete block experimental design, with seven treatments and four replications. Treatments included Control [CO], ammonium nitrate [AN], NS30TM (ammonium nitrate-75% and ammonium sulfate-25% fused mixture) [NS30TM], ammonium nitrate plus ammonium sulfate (ammonium nitrate-75% and ammonium sulfate-25% physical mixture) [AN-AS], urea [UR], urea treated with 0.4% Cu and 0.15% B [UR-CuB], urea treated with 530 mg kg-1 of NBPT [UR-NBPT]. Treatments were applied at rate of 100 kg ha-1 N (except CO). Volatilization losses were quantified up to 30 days after fertilization (DAF). Maximum N-NH3 occurred 16 DAF for UR and UR-CuB and 20 DAF for UR-NBPT. Accumulated N-NH3 losses ranged from 20% (UR), 17% (UR-CuB), and 14% (UR-NBPT) of applied N; non-amidic sources showed losses lower than 1%. Adding urease inhibitor to urea shows potential in reducing volatilization losses even under application over large amounts of straw.

Uma das maneiras de aumentar a eficiência dos fertilizantes nitrogenados, visando, por exemplo, à redução de perdas de amônia por volatilização, é o revestimento desses com polímeros. Objetivou-se avaliar o efeito da aplicação de ureia revestida com polímeros no controle da volatilização de amônia e a sua influência nos componentes da produção na cultura do milho. O experimento foi instalado na safra 2009/10 no município de Uberlândia, MG, em um Latossolo Vermelho-Amarelo (LVA) distrófico textura argilosa. Os tratamentos consistiram na aplicação, em cobertura no milho, de ureia revestida com polímeros e ureia convencional nas doses de 45; 67,5; e 90 kg ha-1 de N, mais um tratamento-controle (sem N), dispostos em blocos casualizados. A aplicação de N influenciou positivamente o teor do nutriente nas folhas e nos grãos, a leitura SPAD e a produtividade de grãos, porém a ureia revestida não alterou as taxas de volatilização de amônia, a leitura SPAD e o teor de N nas folhas e grãos, assim como a produtividade de grãos em relação à aplicação do fertilizante convencional.

A form of increasing the efficiency of N fertilizer is by coating urea with polymers to reduce ammonia volatilization. The aim of this study was to evaluate the effect of polymer-coated urea on the control of ammonia volatilization, yield and nutritional characteristics of maize. The experiment was carried out during one maize growing cycle in 2009/10 on a Geric Ferralsol, inUberlândia, MG, Brazil. Nitrogen fertilizers were applied as topdressing on the soil surface in the following urea treatments: polymer-coated urea at rates of 45, 67.5 and 90 kg ha-1 N and one control treatment (no N), in randomized blocks with four replications. Nitrogen application had a favorable effect on N concentrations in leaves and grains, Soil Plant Analysis Development (SPAD) chlorophyll meter readings and on grain yield, where as coated urea had no effect on the volatilization rates, SPAD readings and N leaf and grain concentration, nor on grain yield in comparison to conventional fertilization.

O preparo mecânico do solo influencia o seu manejo e danifica a estrutura, diminui a porosidade e a infiltração de água e aumenta o escoamento superficial. Utilizando-se simulador de chuvas, estudaram-se os tratamentos, preparo convencional (PC); semeadura direta em resíduo queimado (SQ); semeadura direta em resíduo dessecado (SD); e semeadura direta tradicional em resíduo dessecado (ST), cultivados, além de um preparo convencional sem cultivo do solo (SC - testemunha) e de um campo nativo (CN), em um Nitossolo Háplico no Planalto Sul Catarinense, entre março de 2001 e fevereiro de 2004, com o objetivo de quantificar o escoamento superficial. Ao milho e feijão se aplicaram três testes de chuva em cada um e à soja cinco testes. Quantificaram-se os tempos de início (TI) e pico (TP) de enxurrada, a taxa constante (TE) e o volume de enxurrada (VE) e o coeficiente C da Equação Racional. Os TI, TP e TE, coeficiente C e VE, foram influenciados pelo preparo e cultivo do solo. O TI e o TP foram menores nos tratamentos PC e SC, enquanto a TE, o coeficiente C e o VE, também foram menores, mas nos tratamentos SD e ST. A TE variou de 18 mm h-1 na ST a 44 mm h-1 no SC, enquanto o coeficiente C variou de 0,29 na ST a 0,71 no SC. A variação do VE foi de 106 m³ ha-1 na ST a 434 m³ ha-1 no SC, na média dos cultivos.

Soil tillage influences soil management and damages structure, reduces the porosity and water infiltration and increases surface runoff. A rotating-boom rainfall simulator was used to investigate the treatments: conventional tillage (CT), no-tillage in burn residue (NB), no-tillage in desiccated residue (ND), and traditional no-tillage in desiccated residue (NT), both cropped, as well as conventional tillage without crop (bare soil - BS), and native pasture treatment (NP), in a Typic Hapludox soil, in the Southern Plateau of Santa Catarina State, Brazil, from March, 2001 to February, 2004, with the objective of quantifying surface runoff. Three simulated rainfall tests were applied in maize and bean crops and five in soybean crop. The surface runoff initial time (IT) and surface runoff peak time (PT), the surface runoff constant rate (RR) and surface runoff volume (RV), and C coefficient of the Rational Equation were quantified. The IT, PT, RR, RV and C coefficient changed with soil tillage treatments and with soil cultivation. The IT and PT were smaller in the CT and BS treatments, while the RR, RV and RC were smaller in ND and NT treatments. The RR changed from 18 mm h-1 in NT to 44 mm h-1 in BS treatments, while the RC changed from 0.29 in NT to 0.71 in BS treatments. The VE varied from 106 m³ ha-1 in ND to 434 m³ ha-1 in BS treatments.

O preparo do solo altera as suas condições físicas de superfície e subsuperfície e, conseqüentemente, influencia os valores de propriedades que se relacionam com a erosão hídrica. O trabalho, realizado entre junho de 2005 e março de 2006 em um Nitossolo Háplico alumínico típico, objetivou estudar o efeito de uma escarificação e da erosividade de chuvas sobre algumas variáveis relacionadas à erosão hídrica do solo nos sistemas de manejo: (a) preparo convencional sem cultivo do solo (SCE); (b) preparo convencional (PCE); (c) semeadura direta em solo nunca preparado e com resíduos queimados (SQE); e (d) semeadura direta tradicional (STE). Nos tratamentos PCE, SQE e STE, cultivaram-se aveia-preta, soja, ervilhaca-comum, milho, feijão preto, nabo forrageiro, em rotação durante cinco anos e meio. Após a escarificação, aplicaram-se cinco testes de chuva simulada, com 64 mm h-1 e duração de 20, 30, 40, 50 e 60 min cada um. Entre os testes 2 e 3 de chuva simulada, ocorreram 57 mm de chuva natural; entre os testes 3 e 4, 21 mm; e entre os testes 4 e 5, 30 mm. Determinaram-se o teor de água no solo antes das chuvas, a rugosidade superficial do solo, o tempo de empoçamento e de início da enxurrada, a infiltração de água no solo, o escoamento superficial, a concentração de sedimentos na enxurrada e a perda total de solo. O teor de água do solo praticamente não variou nos tratamentos e nos testes de chuva. A rugosidade superficial foi influenciada pelo manejo anterior do solo, tendo sido menor no SCE do que nos demais tratamentos, sem diferença entre estes. Ao final dos testes de chuva, a rugosidade superficial era menor do que antes do seu início em todos os tratamentos, com exceção do SCE. Esse comportamento da rugosidade influenciou o empoçamento da água da chuva na superfície do solo e, principalmente, o início da enxurrada, refletindo-se também na infiltração de água no solo e no volume de enxurrada. O tratamento STE foi o mais eficaz na redução do volume de enxurrada, na concentração de sedimentos na enxurrada e na perda total de solo. O modelo exponencial do tipo y = a e-bx ajustou-se à taxa de perda de solo e à erosividade das chuvas no tratamento SCE, enquanto em PCE, SQE e STE foi o modelo linear do tipo y = a + bx que se ajustou aos referidos dados.

Tillage changes the physical conditions of the soil surface and subsurface and, consequently, influences values of the parameters related to water erosion. This study aimed to determine, from June 2005 to March 2006, the effect of a chiseling operation and of the rainfall erosivity on some parameters related to the soil water erosion in a Nitosol under the following soil management systems: (a) conventional tillage without soil cultivation (BSE), (b) conventional tillage (CTE), (c) no-tillage in never-tilled soil and with burned crop residue (NQE), and (d) traditional no-tillage (NTE). In CTE, NQE and NTE treatments, black oat, soybean, vetch, corn, oat, bean, fodder radish, soybean, vetch, corn and oat were cropped in rotation during five and a half years. After chiseling, five rainfall tests were simulated (intensity of 64 mm h-1) during 20, 30, 40, 50 and 60 min. Between the second and third test there was 57 mm natural rainfall, 21 mm between the third and fourth test, and 30 mm between the fourth and fifth test. Soil moisture content, surface roughness, time of puddle formation and the beginning of runoff, soil water infiltration, total runoff, sediment concentration in runoff, and total soil loss were determined prior to each rainfall test. There was virtually no variation in soil water content in the treatments and rainfall tests. The surface roughness was influenced by the previous soil management and was lower in BSE than in the other treatments, which did not differ from each other. At the end of the rainfall tests, the soil surface roughness was lower than at the beginning in all treatments, except in BSE. This roughness pattern influenced the puddling of rainfall water on the soil surface, and especially the beginning of runoff, and affected the soil water infiltration and runoff volume. The NTE treatment was the most effective to reduce the runoff volume, sediment concentration in the runoff and total soil loss. The exponential model (y = a e-bx) was adjusted to soil loss and rainfall erosivity data for the soil without cultivation. Data from the soil under conventional soil tillage, no-tillage with residue burning and no-tillage with residue maintenance, it was adjusted a linear model (y = a + bx).

A rugosidade superficial do solo é influenciada, entre outros fatores, pelo efeito residual de manejo do solo, pelo tipo de preparo e pela erosividade da chuva e, juntamente com a cobertura do solo por resíduos vegetais, influencia a erosão hídrica. O objetivo deste trabalho foi determinar, entre junho de 2005 e março de 2006, em um Nitossolo Háplico alumínico típico, o efeito de uma operação de escarificador e da erosividade de chuvas sobre a rugosidade superficial, nos seguintes sistemas de manejo do solo: preparo convencional sem cultivo do solo (SCE), preparo convencional com cultivo do solo (PCE), semeadura direta em solo nunca preparado e com resíduos queimados (SQE) e semeadura direta tradicional (STE). Nos tratamentos PCE, SQE e STE, cultivaram-se aveia-preta, soja, ervilhaca comum, milho, aveia-preta, feijão preto, nabo forrageiro, soja, ervilhaca comum, milho e aveia-preta. Aplicaram-se cinco testes de chuva simulada, com 64 mm h-1 e duração de 20, 30, 40, 50 e 60 min cada um. Entre o segundo e o terceiro teste de chuva simulada ocorreram 57 mm de chuva natural; entre o terceiro e o quarto, 21 mm; e entre o quarto e o quinto, 30 mm. Determinou-se a rugosidade superficial imediatamente antes e logo após o preparo do solo com escarificador e imediatamente após cada teste de chuva simulada. A rugosidade original e linear da superfície do solo não foi influenciada pelo manejo, enquanto a rugosidade ao acaso teve essa influência, ao final de um pousio de seis meses. Diferentes sistemas de manejo do solo mantidos em pousio por seis meses resultaram em diferente rugosidade original, linear e ao acaso, quando o solo foi submetido à operação de escarificador. A rugosidade ao acaso foi menos influenciada pela declividade do terreno do que pelas marcas de preparo do solo, tendo diminuído com o aumento da erosividade das chuvas. Essa mesma rugosidade apresentou coeficiente de decaimento temporal semelhante nos sistemas de manejo do solo semeadura direta e preparo convencional.

Surface soil roughness is affected by many factors, such as the residual effect of the soil management, tillage and rainfall erosivity and, together with the soil cover of crop residues, influences water erosion. The objective of this study was to determine the effects of a chiseling operation, together with rainfall erosivity, on soil surface roughness, from June 2005 to March 2006, in an aluminic Typical Hapludox, under the following soil management systems: bare soil under conventional tillage (BCT), cultivated soil under conventional tillage (CCT), no-tillage in a never-tilled soil with burnt plant residues (BNT), and traditional no-tillage (TNT). The crop sequence in the treatments CCT, BNT and TNT was black oat, soybean, common vetch, corn, black oat, common bean, fodder radish, soybean, common vetch, corn and black oat. Five simulated rain tests were applied, with a constant intensity of 64 mm h-1 and durations of 20, 30, 40, 50, and 60 min each. Natural rains during the experimental period accounted for 57 mm, between the 2nd and 3rd rainfall test; 21 mm, between the 3rd and 4th test; and, 30 mm, between the 4th and 5th test. The surface roughness was determined immediately before and immediately after the chiseling tillage, and immediately after each test of rain simulation. The original and linear soil surface roughness was not influenced by the management, unlike random roughness, at the end of a six-month fallow period. The original, linear and random roughness in different soil management systems was affected by a six-month fallow period, when the soil was subjected to chiseling. Random roughness was less influenced by soil slope than by tillage marks, which decreased with the increasing rainfall erosivity. The coefficient of decay of this kind of soil roughness was similar in the studied soil management systems under no tillage and conventional tillage.