César de Castro

Glyphosate reduces shoot concentrations of mineral nutrients in glyphosate-resistant soybeans.

Although glyphosate-resistant (GR) technology is used in most countries producing soybeans (Glycine max L.), there are no particular fertilize recommendations for use of this technology, and not much has been reported on the influence of glyphosate on GR soybean nutrient status. An evaluation of different cultivar maturity groups on different soil types, revealed a significant decrease in macro and micronutrients in leaf tissues, and in photosynthetic parameters (chlorophyll, photosynthetic rate, transpiration and stomatal conductance) with glyphosate use (single or sequential application). Irrespective of glyphosate applications, concentrations of shoot macro- and micronutrients were found lower in the near-isogenic GR-cultivars compared to their respective non-GR parental lines Shoot and root dry biomass were reduced by glyphosate with all GR cultivars evaluated in both soils. The lower biomass in GR soybeans compared to their isogenic normal lines probably represents additive effects from the decreased photosynthetic parameters as well as lower availability of nutrients in tissues of the glyphosate treated plants.

ESTABLISHING MANAGEMENT ZONES USING SOIL ELECTRICAL CONDUCTIVITY AND OTHER SOIL PROPERTIES BY THE FUZZY CLUSTERING TECHNIQUE

The design of site-specific management zones that can successfully define uniform regions of soil fertility attributes that are of importance to crop growth is one of the most challenging steps in precision agriculture. One important method of so proceeding is based solely on crop yield stability using information from yield maps; however, it is possible to accomplish this using soil information. In this study the soil was sampled for electrical conductivity and eleven other soil properties, aiming to define uniform site-specific management zones in relation to these variables. Principal component analysis was used to group variables and fuzzy logic classification was used for clustering the transformed variables. The importance of electrical conductivity in this process was evaluated based on its correlation with soil fertility and physical attributes. The results confirmed the utility of electrical conductivity in the definition of management zones and the feasibility of the proposed method.

Períodos de interferência de plantas daninhas na cultura do girassol

Two experiments were carried out at Embrapa Soybean, Londrina, Paraná Brazil, to evaluate the effect of different periods of control or coexistence of weeds on sunflower crop, considering oil yield and seed yield. The experimental design was completly arranged in randomized blocks, with four replicates. The treatments for both experiments were maintaining the crop either with or without weeds for 7, 14, 21, 28, 42, 49, 56, 70, 84 and 118 days after crop emergence (DAE), during the entire cycle. The weed comunity was composed by hairy beggarticks (Bidens subalternans) and volunteer wheat. Weed densities and dry matter weight were determined, as well as oil yield and grain yield. Weed presence caused a yield daily loss of 1.1 and 2.5 kg ha-1 of oil yield and seed yield, respectively, whereas weed absence provided a daily gain of 6.5 kg ha-1 for oil yield and 14.4 kg ha-1 for seed yield. Weed crop coexistence for up to 21 DAE did not cause any negative effect on oil and seed yields, and the maximum length of time in which the weeds had to be controlled to prevent crop yield losses was 30 days after emergence. The critical period of interference was from 21 to 30 DAE.

Marcha de absorção de macronutrientes na cultura do girassol

This study aimed to establish curves of macronutrient accumulation in sunflower. The experiment was conducted in the field on a Typic Hapludox, at the experimental station of Embrapa Soja in Londrina, State of Parana. The plots consisted of 14 25 m long rows spaced 0.70 m apart, resulting in a total area of 245 m2, with four replications. Prior to sowing a fertilization seeding of 300 kg ha-1 of 05-20-20 NPK fertilizer was applied. Fertilization was split in two applications of 25 + 1 kg ha-1 N and B, which were applied 21 and 35 days after sowing, respectively. The hybrid BRS 191 and a final plant density of 40,000 plants ha-1 were used. Plant samples were collected every two weeks after emergence and separated in the different parts (petioles, leaves, stems and, when applicable, capitula and achenes). After drying, each plant part was weighed and ground to determine the N, P, K, Ca, Mg, and S content. From the contents of these nutrients and dry mass of each plant, the accumulation curve was obtained. It was found that for yields > 3,000 kg ha-1, BRS 191 extracted about 150, 24, 286, 116, 42, and 24 kg ha-1 of N, P, K, Ca, Mg, and S, respectively, in the following order of extraction: K> N> Ca> P = S. In addition to the relation to exportation, the nutrient order was: N> P = K> S = Mg> Ca. Therefore, special attention should be paid to the maintenance of an adequate supply of N, K and Ca, due to the high demand of sunflower.

Boron and water stress on yield of sunflower

Com este trabalho, objetivou-se estudar sob condicoes de casa-de-vegetacao, o efeito da interacao doses boro e estresse hidrico na producao de materia seca total, producao de aquenios e conteudo de oleo em girassol cultivado em Latossolo Vermelho Amarelo distrofico de textura media. O delineamento experimental utilizado foi o de blocos ao acaso, em esquema fatorial 4 x 4, com quatro repeticoes. Foram estudadas quatro doses de B: 0, 0,25, 0,5 e 2,0 mg kg-1, aplicado na forma de acido borico e quatro fases de controle de umidade: sem estresse hidrico durante o ciclo, com estresse hidrico durante o ciclo, estresse hidrico a partir do florescimento e estresse hidrico a partir do enchimento de aquenios. Os resultados mostraram que, independentemente da fase de aplicacao ou nao de estresse hidrico, a dose 0,5 mg dm-3 de B acarretou na maior producao de materia seca total, producao de aquenios e rendimento de oleo por capitulo. A aplicacao de estresse hidrico a partir do inicio do florescimento ou no enchimento de aquenios acarreta em menor producao de materia seca total, de aquenios e de oleo.Com este trabalho, objetivou-se estudar sob condicoes de casa-de-vegetacao, o efeito da interacao doses boro e estresse hidrico na producao de materia seca total, producao de aquenios e conteudo de oleo em girassol cultivado em Latossolo Vermelho Amarelo distrofico de textura media. O delineamento experimental utilizado foi o de blocos ao acaso, em esquema fatorial 4 x 4, com quatro repeticoes. Foram estudadas quatro doses de B: 0, 0,25, 0,5 e 2,0 mg kg-1, aplicado na forma de acido borico e quatro fases de controle de umidade: sem estresse hidrico durante o ciclo, com estresse hidrico durante o ciclo, estresse hidrico a partir do florescimento e estresse hidrico a partir do enchimento de aquenios. Os resultados mostraram que, independentemente da fase de aplicacao ou nao de estresse hidrico, a dose 0,5 mg dm-3 de B acarretou na maior producao de materia seca total, producao de aquenios e rendimento de oleo por capitulo. A aplicacao de estresse hidrico a partir do inicio do florescimento ou no enchimento de aquenios acarreta em menor producao de materia seca total, de aquenios e de oleo.

Doses e métodos de aplicação de nitrogênio em girassol

A sunflower field experiment was carried out during the growing seasons of 1991/92; 92/93 and 93/94, on an Typic Eutrorthox. The applied levels of nitrogen (N) were 0, 30, 60 and 90 kg ha-1 and the application methods were: 1. incorporated/moldboard plow (broadcasted with incorporation with moldboard plow down to 30 cm depth before sowing); 2. incorporated/disk bars (broadcasted with incorporation with disk bars before seedbed preparation); 3. incorporated/grade/split (30% of N broadcasted with incorporation with disk bars before seedbed preparation and the remaining N 30 days after the sunflower emergency). The effect of different levels and methods of N supply were evaluated through grain yield, weight of 1,000 achenes, plant height, and stem diameter. Phosphorus and potassium were applied together with N fertilization. The experimental design was a randomized blocks with split-plots and four replicates, with N rates in the main plots and methods in the split-plots. A density of 42,857 plants ha-1 occupied a total area of 3,528 m2. Grain yield increased with N levels up to 90 kg ha-1, while the economic level was obtained with 17.5 kg ha-1 of N. The highest grain yield and 1,000 achenes weight were achieved during the 1993/94 season, while the highest plant height and stem diameter were obtained in 1991/92. Different methods of N application did not affect grain yield. On the other hand, the greatest 1.000 achenes weight was obtained with the incorporated/grade/split method of N incorporation. However, for the other variables N incorporation with moldboard plow gave greater values.

Optimal Acidity Indices for Soybean Production in Brazilian Oxisols

Soybean is an important crop for the Brazilian economy, and soil acidity is one of the main yield-limiting factors in Brazilian Oxisols. A field experiment was conducted during three consecutive years with the objective to determine soybean response to liming grown on Oxisols. Liming rates used were 0, 3, 6, 12, and 18 Mg ha−1. Liming significantly increased grain yield in a quadratic trend. Ninety percent maximum economic grain yield (2900 kg ha−1) was achieved with the application of about 6 Mg lime ha−1. Shoot dry weight, number of pods per plant, and 100-grain weight were also increased significantly in a quadratic fashion with increasing liming rate from 0 to 18 Mg ha−1. These growth and yield components had a significant positive association with grain yield. Maximum contribution in increasing grain yield was of number of pods per plant followed by grain harvest index and shoot dry weight. Uptake of nitrogen (N) was greatest and phosphorus (P) was least among macronutrients in soybean plant. Nutrient-use efficiency (kg grain per kg nutrient accumulation in grain) was maximum for magnesium (Mg) and lowest for N among macronutrients. Application of 3 Mg lime ha−1 neutralized all aluminum ions in soil solution. Optimal acidity indices for 90% of maximum yield were pH 6.0, calcium (Ca) 1.6 cmolc kg−1, Mg 0.9 cmolc kg−1, base saturation 51%, cation exchange capacity (CEC) 4.8 cmolc kg−1, Ca/Mg ratio 1.9, Ca / potassium (K) ratio 5.6, and Mg/K ratio 3.0.

Sunflower micronutrient uptake curves

Devido ao fato de a maioria dos trabalhos encontrados na literatura a respeito do acumulo dos micronutrientes [zinco (Zn), manganes (Mn), ferro (Fe), cobre (Cu) e boro (B)] no girassol serem antigos, objetiva-se, com este trabalho estabelecer curvas de acumulo de micronutrientes em um hibrido de girassol na condicao edafoclimatica dos tropicos. O experimento foi instalado no campo sobre Latossolo Vermelho distroferrico de textura argilosa, localizado na fazenda experimental da Embrapa Soja, em Londrina-PR, utilizando o hibrido comercial BRS 191. O delineamento experimental utilizado foi o inteiramente casualizado, com quatro repeticoes. As unidades experimentais foram constituidas de 14 linhas, com espacamento de 0,70 m entre linhas e 25 m de comprimento, com densidade final de 42.858 plantas ha-1. As amostras das plantas foram coletadas em intervalos de 14 dias apos a emergencia. Apos cada coleta, dividiram-se as plantas em peciolo, folha, caule, capitulo e aquenios, sendo que as mesmas foram secas ate peso constante, quando foram tomados os pesos da materia seca e determinados os teores de Zn, Mn, Fe, Cu e B no tecido vegetal. A absorcao de micronutrientes ocorreu em maior velocidade a partir dos 42 dias apos a emergencia (DAE). O Fe foi o micronutriente mais absorvido, acumulando maior quantidade tanto nos aquenios como em relacao ao total absorvido. O acumulo total de Fe, Mn, Zn, B e Cu foram 38,06, 19,68, 9,20, 8,62 e 4,27 mg planta-1, respectivamente.

Response of Soybean to Phosphorus Fertilization in Brazilian Oxisol

Soybean is an important grain crop for Brazil, and phosphorus (P) plays an important role in improving yield of this crop in Brazilian Oxisols. Data are limited on influence of P sources and rate on soybean yield, yield components, and P-use efficiency. A field experiment was conducted for 3 consecutive years to determine response of soybean to three fertilizers (single superphosphate, Yoorin, and Arad) with 0, 17.5, 35, and 52.5 kg P ha−1 (0, 40, 80 and 120 kg P2O5 ha−1). Grain yield was significantly influenced by phosphorus fertilization. Overall, maximum grain yield was produced by application of single superphosphate, followed by Yoorin and Arad. Number of grains per pod and 100-grain weights were also influenced significantly by P fertilization. Shoot dry weight, number of pods per plant, and grain harvest index had a significant positive association with grain yield. Phosphorus uptake in grain was about six times more than uptake in shoots, and P uptake in grain had a significant positive association with grain yield. Phosphorus-use efficiency (kg grain/kg P applied or uptake) decreased with increasing P rate, and it was greater for single superphosphate than for Yoorin and Arad sources of P fertilization. However, P-utilization efficiency (kg grain plus straw yield / P uptake in grain plus straw) was greater under Yoorin treatment compared to the two other sources of P.

Boron extraction and vertical mobility in Paraná State oxisol, Brazil

The deficiency or excess of micronutrients has been determined by analyses of soil and plant tissue. In Brazil, the lack of studies that would define and standardize extraction and determination methods, as well as lack of correlation and calibration studies, makes it difficult to establish limits of concentration classes for analysis interpretation and fertilizer recommendations for crops. A specific extractor for soil analysis is sometimes chosen due to the ease of use in the laboratory and not in view of its efficiency in determining a bioavailable nutrient. The objectives of this study were to: (a) evaluate B concentrations in the soil as related to the fertilizer rate, soil depth and extractor; (b) verify the nutrient movement in the soil profile; (c) evaluate efficiency of Hot Water, Mehlich-1 and Mehlich-3 as available B extractors, using sunflower as test plant. The experimental design consisted of complete randomized blocks with four replications and treatments of five B rates (0, 2, 4, 6, and 8 kg ha -1 ) applied to the soil surface and evaluated at six depths (0–0.05, 0.05–0.10, 0.10–0.15, 0.15–0.20, 0.20–0.30, and 0.30–0.40 m). Boron concentrations in the soil extracted by Hot Water, Mehlich-1 and Mehlich-3 extractors increased linearly in relation to B rates at all depths evaluated, indicating B mobility in the profile. The extractors had different B extraction capacities, but were all efficient to evaluate bioavailability of the nutrient to sunflower. Mehlich1 and Mehlich-3 can therefore be used to analyze B as well as Hot Water.