ABSTRACT Foliar fertilization can be recommended to treat boron (B) deficiency in coffee and cotton. Considering that B foliar fertilizers with polyol-boron complexes can affect B uptake and mobility differently within the plant, and coffee and cotton have different cuticles and stomata density, a differential response would be expected. We aimed to study the foliar application of boric acid combined with sorbitol on B uptake and translocation in cotton and coffee. Green-house grown plants received B as boric acid and a sorbitol-monoethanolamine complex and were sampled up to 96 h after application. Boron absorption was fast, reaching 60 and 80 % in cotton and coffee 96 h after application, respectively. Uptake rates and total B absorption were similar for the fertilizers. The proportion of B taken up by coffee is greater than by cotton likely because of the greater stomata density in coffee and less likely due to the higher amount of wax in cotton cuticle. Boron remobilization is higher in coffee as compared with cotton. Sorbitol seems to increase B transport in the transpiratory stream of cotton, but impairs remobilization in the phloem since B translocation to roots is decreased in both cotton and coffee.

ABSTRACT Since there is no consensus on phosphogypsum (PG) rates to be used in agriculture, a better understanding of its effects on the soil solution is needed. Cotton root growth was evaluated as related to Al and Ca activity in soil solution affected by PG. The experiment was carried out in rhizotrons filled with30∙dm–3 of soil. PG rates were estimated by multiplying the soil clay content by 0.0, 1.5, 3.0, 6.0 and 12.0, and it was mixed to the sub-soil.In the upper soil layer, limestone was applied. After 90 days, samples were taken for analysis, and cotton was planted. After27 days, plants were harvested. PG increased soil pH and decreased Al content and activity. Without PG, dissolved organic carbon concentration was high in the soil solution, which explains the predominance of carbon Al-complexed with PG application. From 1,680 kg∙ha–1 of PG (corresponding to 6 × clay content), sulphur and calcium had the highest concentrations, increasing the SO4 Al-complexed. Cotton root length decreased in the upper layer and increased in the subsoil up to 2,324 kg∙ha–1 (corresponding to 8.3 × clay content) of PG. Cotton root growth is better related with soil properties than with soil solution attributes, and the present recommendations for PG use based on soil clay content underestimate the rate to be applied.

ABSTRACT Safflower (Carthamus tinctorius L.) is a commercial seed crop grown for its good yield of high-quality oil. It is tolerant to water stress but may be sensitive to soil compaction. The aim of this study was to assess safflower growth under different degrees of soil compaction at depths of 0.15 m to 0.20 m. The experiment was carried out in PVC pots constructed from three rings. Five levels of penetration resistance (0.20, 0.33, 0.50, 0.93, and 1.77 MPa) were applied in the intermediate ring, and two safflower genotypes, IMA-4904 and IMA-2106, were examined. There was no difference between safflower genotypes with respect to their resistance to soil compaction, which reduced root length density in the compacted layer and changed the root distribution in the soil profile, but did not prevent the roots from crossing the compacted layer and developing in depth. Increased soil bulk density in the compacted layer increased root diameter of the IMA-2106 genotype. Penetration resistance levels over 0.20 MPa (density of 1.2 mg.dm–3) limited safflower root development. The maximum safflower growth occurred when the soil penetration resistance was 0.86 MPa. In this study, the Q1/2 index was higher than 1.77 and 1.55 for the IMA-2106 and IMA-4904 genotypes, respectively. Hence, safflower has proven to be tolerant to soil compaction, and stands out as a species with potential to decrease soil bulk density.

RESUMO O guar (Cyamopsis tetragonoloba L.) é comumente cultivado em terras áridas, por ser altamente tolerante à seca. No entanto, a compactação do solo pode ser um fator limitante ao seu cultivo. Objetivou-se avaliar o crescimento de guar, em função da resistência do solo à penetração (0,20 Mpa; 0,33 Mpa; 0,50 Mpa; 0,93 Mpa; e 1,77 Mpa, em camada com profundidade entre 0,15 m e 0,20 m), em Latossolo Vermelho Distroférrico. Avaliaram-se a massa seca da parte aérea e raiz, o comprimento radicular a partir do índice Q1/2 (resistência mecânica do solo à penetração na qual o crescimento radicular é reduzido à metade) e o diâmetro radicular. O crescimento da parte aérea de guar começa a ser prejudicado por resistência superior a cerca de 1 MPa. A compactação do solo altera a distribuição das raízes de guar no perfil do solo, concentrando-as na camada de 0,15 m, mas não impede que as raízes penetrem nessa camada e se desenvolvam em profundidade. O diâmetro de raiz aumenta na camada compactada. A resistência à penetração no solo de até 1,77 MPa não influencia na densidade de comprimento radicular abaixo da camada compactada, bem como na densidade de comprimento radicular total de guar. Embora o índice Q1/2 de guar seja superior a 1,58, a massa seca da parte aérea e da raiz são prejudicadas.

ABSTRACT Guar (Cyamopsis tetragonoloba L.) is commonly grown in arid lands, because of its high drought-tolerance. However, soil compaction may be a limiting factor to its growth. This study aimed to evaluate the guar growth, according to the soil penetration resistance (0.20 MPa, 0.33 MPa, 0.50 MPa, 0.93 MPa and 1.77 MPa, in a layer with depth between 0.15 m and 0.20 m), in a Rhodic Acrudox soil. The shoot and root dry mass, root length by the Q1/2 index (mechanical soil penetration resistance in which the root growth is reduced by 50 %) and root diameter were evaluated. The impairment of the guar shoot growth begins when the penetration resistance is greater than around 1 MPa. The soil compaction alters the distribution of guar roots in the soil profile, concentrating them in the 0.15 m layer, but it does not prevent roots from penetrating this layer and developing in depth. The root diameter increases in the compacted layer. A soil penetration resistance of up to 1.77 MPa does not influence the root length density below the compacted layer, as well as the total root length density of guar. Although the guar Q1/2 index is greater than 1.58, the shoot and root dry mass are impaired.

ABSTRACT: In addition to improving sustainability in cropping systems, the use of a spring and winter crop rotation system may be a viable option for mitigating soil CO2 emissions (ECO2). This study aimed to determine short-term ECO2 as affected by crop rotations and soil management over one soybean cycle in two no-till experiments, and to assess the soybean yields with the lowest ECO2. Two experiments were carried out in fall-winter as follows: i) triticale and sunflower were grown in Typic Rhodudalf (TR), and ii) ruzigrass, grain sorghum, and ruzigrass + grain sorghum were grown in Rhodic Hapludox (RH). In the spring, pearl millet, sunn hemp, and forage sorghum were grown in both experiments. In addition, in TR a fallow treatment was also applied in the spring. Soybean was grown every year in the summer, and ECO2 were recorded during the growing period. The average ECO2 was 0.58 and 0.84 g m2 h–1 with accumulated ECO2 of 5,268 and 7,813 kg ha–1 C-CO2 in TR and RH, respectively. Sunn hemp, when compared to pearl millet, resulted in lower ECO2 by up to 12 % and an increase in soybean yield of 9% in TR. In RH, under the winter crop Ruzigrazz+Sorghum, ECO2 were lower by 17%, although with the same soybean yield. Soil moisture and N content of crop residues are the main drivers of ECO2 and soil clay content seems to play an important role in ECO2 that is worthy of further studies. In conclusion, sunn hemp in crop rotation may be utilized to mitigate ECO2 and improve soybean yield.

ABSTRACT: Ruzigrass (Urochola ruziziensis) has a large capacity to take up K from the soil, including non-exchangeable forms, and can play an important role in nutrient cycling in integrated production systems. However, K transport to roots of brachiarias is not well known, nor the nutrient dynamics in the rhizosphere, where a concentration gradient may be established towards the non-rhizospheric soil, creating a favorable environment for the release of non-exchangeable K. This study aimed to evaluate the effect of ruzigrass on K dynamics in the rhizosphere and on non-exchangeable K release. Ruzigrass was grown in pots filled with a Latossolo Vermelho Amarelo (Typic Hapludox) that was collected at 0.00-0.20 and 0.20-0.60 m layer from a cultivated area and fertilized with 0, 30, and 60 mg kg−1 of K, plus a treatment with forest soil, used as control. Thirty days after plant emergence, soil samples were taken at the following distances from the roots: 0.5, 1.0, 1.5, 3.0, 5.0, and 10.0 mm. For the highest exchangeable K rate (60 mg dm−3), the exchangeable K level was higher from 0 to 0.5 mm of the roots for both soils (0.00-0.20 and 0.20-0.60 m). Therefore, more K was transported to the rhizosphere than the plant could take up. A depletion of exchangeable K observed in the rhizosphere resulted in the release of K from non-exchangeable forms, as observed in the soils from 0.00-0.20 (60 mg dm−3) and 0.20-0.60 m (without application of K). Ruzigrass grown on low K soils without fertilizer application results in a larger exchangeable K depletion zone than in soils that were fertilized or originally high in exchangeable K, showing a high potential for K cycling in the system.

RESUMO O manejo de reguladores de crescimento tem sido um desafio para cotonicultores, devido ao aumento da instabilidade climática e adoção de cultivares precoces, em segunda safra. Objetivou-se propor um novo método, denominado Taxa de Crescimento da Cultura, para definir doses de cloreto de mepiquate em lavouras de algodão, bem como compará-lo com práticas de manejo tradicionais. Exceto para micronaire, não houve diferença nos parâmetros de crescimento do algodoeiro e nem na produtividade e qualidade de fibra, entre o novo método e o tradicional. As doses de cloreto de mepiquate foram, em média, 24 % maiores e 43 % menores em cultivares tardias e precoces, respectivamente, no novo método. O número de capulhos em plantas tratadas com cloreto de mepiquate foi menor do que nas plantas não tratadas, nas cultivares IMA5672B2RF e IMA5675B2RF, mas o peso médio do capulho foi maior nestes genótipos. O novo método é eficiente na definição da dose de regulador de crescimento para evitar crescimento excessivo em cultivares de algodão e resulta em menos cloreto de mepiquate aplicado a cultivares precoces, preservando-se a produtividade e a qualidade da fibra.

ABSTRACT Plant growth regulator management has been a challenge for cotton growers, due to the increased weather instability and the adoption of early cultivars, in off-season crops. This study aimed at proposing a new method, called Crop Growth Rate, to define mepiquat chloride rates in cotton crops, as well as to compare it with traditional management practices. Except for micronaire, there was no difference in cotton growth parameters, neither in yield nor fiber quality, between the new method and the traditional one. The mepiquat chloride rates were, on average, 24 % higher and 43 % lower in late and early maturity cultivars, respectively, for the new method. The number of bolls in plants treated with mepiquat chloride was lower than in non-treated plants, for the IMA5672B2RF and IMA5675B2RF cultivars, but a higher average weight of bolls was observed for these genotypes. The new method is efficient in defining the plant growth regulator rate to avoid an excessive growth and results in less mepiquat chloride applied to early cycle cultivars, preserving lint yield and fiber quality.

ABSTRACT Oxidic soils are phosphorus drains in soil; hence, P availability is a limiting factor in tropical, weathered Oxidic soils. It has been shown that some brachiarias grown as cover crops may increase soil available P to subsequent crops. The objective of this study was to evaluate soil P cycling and availability, as well as the response of soybean to soluble and natural reactive phosphates as affected by ruzi grass (Urochloa ruziziensis, R. Germ. and C.M. Evrard, Crin) grown as a cover crop in a no-till system. Experimental treatments consisted of the presence or absence of ruzi grass in combination with a control (0.0 P) and soluble and reactive rock phosphate broadcast on the soil surface in the winter (80 kg ha-1 P2O5), plus three rates of P applied to soybean furrows (0, 30, and 60 kg ha-1 of P2O5) at planting, in the form of triple superphosphate. Soybean was cropped in two seasons: 2010/2011 and 2011/2012. Soil samples were taken before soybean planting (after desiccation of Brachiaria) at 0.00-0.05 and 0.05-0.10 m for soil available P. Total weight of dry matter and P accumulated in ruzi grass were determined, as well as soybean yields, P in soybean grains, and P use efficiency (PUE). The use of natural phosphate increased soil P availability. The highest yields were obtained with higher application rates of triple superphosphate in the planting furrow combined with broadcast rock phosphate. Broadcast application of Arad reactive phosphate increases and maintains soil available P, and this practice, associated with ruzi grass grown as a cover crop and the use of triple superphosphate applied to soybean furrows, results in higher use of P by soybeans.

A fixação de fósforo em solos tropicais pode ser diminuída sob plantio direto. Nesse caso, o fertilizante poderia ser aplicado na superfície do solo, o que melhoraria o rendimento operacional pela diminuição do reabastecimento da semeadora com fertilizantes. Em longo prazo, fontes de P menos solúveis poderiam ser viáveis. Nesse experimento, o efeito da aplicação de P em superfície, tanto o fosfato solúvel como reativo, sobre as formas de P no solo e a disponibilidade para a soja foram estudados em combinação com a aplicação de P solúvel nos sulcos de semeadura, em um experimento de longa duração, onde a soja foi cultivada em rotação com braquiária (Brachiaria ruziziensis). Fertilizantes fosfatados foram aplicados na superfície de um solo com histórico de aplicações de P, nas doses 0,0 e 80,0 kg ha-1, na forma de superfosfato triplo ou fosfato Arad. Amostras de solo foram tomadas até 60 cm de profundidade, e o P do solo foi fracionado. A soja foi cultivada com 0, 30 e 60 kg ha-1 de P2O5 como superfosfato triplo aplicado no sulco da semente. Ambos os fertilizantes aplicados em superfície aumentaram o P disponível nas camadas superiores do solo e as formas moderadamente lábeis orgânica e inorgânica de P no perfil do solo, provavelmente como resultado do apodrecimento radicular. A soja respondeu aos fosfatos aplicados na superfície do solo ou no sulco de semeadura; no entanto, a aplicação de P solúvel no sulco não deve ser descartada. Em solos tropicais, com uma história de fertilização fosfatada, fontes de P solúveis podem ser substituídas por fosfatos naturais reativos aplicados à superfície do solo. A operação de semeadura pode ser agilizada pela redução da taxa de P aplicada ao sulco da sementeira, em relação às doses que são empregadas atualmente.

Phosphorus fixation in tropical soils may decrease under no-till. In this case, P fertilizer could be surface-spread, which would improve farm operations by decreasing the time spend in reloading the planter with fertilizers. In the long term, less soluble P sources could be viable. In this experiment, the effect of surface-broadcast P fertilization with both soluble and reactive phosphates on soil P forms and availability to soybean was studied with or without fertilization with soluble P in the planting furrow in a long-term experiment in which soybean was grown in rotation with Ruzigrass (Brachiaria ruziziensis). No P or 80 kg ha-1 of P2O5 in the form of triple superphosphate or Arad reactive rock phosphate was applied on the surface of a soil with variable P fertilization history. Soil samples were taken to a depth of 60 cm and soil P was fractionated. Soybean was grown with 0, 30, and 60 kg ha-1 of P2O5 in the form of triple phosphate applied in the seed furrow. Both fertilizers applied increased available P in the uppermost soil layers and the moderately labile organic and inorganic forms of P in the soil profile, probably as result of root decay. Soybean responded to phosphates applied on the soil surface or in the seed furrow; however, application of soluble P in the seed furrow should not be discarded. In tropical soils with a history of P fertilization, soluble P sources may be substituted for natural reactive phosphates broadcast on the surface. The planting operation may be facilitated through reduction in the rate of P applied in the planting furrow in relation to the rates currently applied.

Some plant species can change soil phosphorus (P) availability and this may be an important tool in managing tropical high fixing phosphorus soils. An experiment was conducted to evaluate phosphorus transformations in the soil and phosphatase activity during periods of Congo grass (Brachiaria ruziziensis, Germain et Evrard) growth in two tropical soils receiving 20, 40, 80, 160 mg dm-3 of inorganic P. Plants were grown for 84 days in 8-L pots. Acid phosphatase activity, P in the microbial mass, soil organic and inorganic P and P accumulation by Congo grass were evaluated. Phosphorus fertilization increased soil P availability, Congo grass yields and P accumulation in the plant. On average, less labile P forms in the soil were not changed by Congo grass; however, the P in the soil extracted with HCl (P-Ca - non labil form) decreased. This decrease may have resulted from the combination of the presence of grass and phosphatase capacity to dissolve less available P in the soil. Thus, soil exploration by Congo grass roots and the subsequent extraction of calcium phosphate may have increased the P concentration in the plant tissue. Despite the decrease in the P extracted from the soil with HCl resulting in increased labile P forms in the soil, the effect of Congo grass on the availability of P depends on the soil type.

O fornecimento de P para as culturas em solos tropicais é deficiente em razão da sua natureza pouco solúvel no solo; e a adição de fertilizantes fosfatados é necessária para obter-se alta produtividade. O objetivo deste estudo foi examinar os mecanismos pelos quais uma planta de cobertura (Braquiária - Brachiaria ruziziensis) cultivada em rotação com soja pode melhorar a disponibilidade do P de fertilizantes e do solo, utilizando ensaios de campo de longo prazo e abordagens de laboratório com fracionamento químico do P. O campo experimental vinha sendo cultivado com soja em rotação com diversas espécies sob semeadura direta há seis anos. Doses de 0 ou 240 kg ha-1 de P2O5, como superfosfato triplo ou fosfato reativo de Arad, haviam sido aplicadas. Em abril de 2009, foram aplicados novamente 0 e 80 kg ha-1 de P2O5, às mesmas parcelas, quando foi semeada B. ruziziensis. Em novembro de 2009, após a dessecação da braquiária, amostras de solo foram coletadas nas camadas de 0-5 e 5-10 cm, e o P foi fracionado. O P disponível do solo aumentou em profundidade com o cultivo de B. ruziziensis na presença de fertilizantes fosfatados. A relação C/P também foi aumentada pela planta de cobertura. O cultivo de B. ruziziensis elevou os teores de P na fração húmica do solo. A B. ruziziensis aumenta a disponibilidade de P no solo por prevenir a fixação do P aplicado como fertilizante e manter o P em formas orgânicas.

The phosphorus supply to crops in tropical soils is deficient due to its somewhat insoluble nature in soil, and addition of P fertilizers has been necessary to achieve high yields. The objective of this study was to examine the mechanisms through which a cover crop (Congo grass - Brachiaria ruziziensis) in rotation with soybean can enhance soil and fertilizer P availability using long-term field trials and laboratory chemical fractionation approaches. The experimental field had been cropped to soybean in rotation with several species under no-till for six years. An application rate of no P or 240 kg ha-1 of P2O5 had been applied as triple superphosphate or as Arad rock phosphate. In April 2009, once more 0.0 or 80.0 kg ha-1 of P2O5 was applied to the same plots when Congo grass was planted. In November 2009, after Congo grass desiccation, soil samples were taken from the 0-5 and 5-10 cm depth layer and soil P was fractionated. Soil-available P increased to the depth of 10 cm through growing Congo grass when P fertilizers were applied. The C:P ratio was also increased by the cover crop. Congo grass cultivation increased P content in the soil humic fraction to the depth of 10 cm. Congo grass increases soil P availability by preventing fertilizer from being adsorbed and by increasing soil organic P.

O objetivo deste trabalho foi avaliar a eficácia da braquiária (Urochloa ruziziensis) em aumentar a disponibilidade de P, em solo de áreas fertilizadas com fosfatos solúveis ou reativos. A área havia sido cultivada em semeadura direta por cinco anos, em sistema de cultivo com soja, triticale/aveia-preta e milheto. Previamente ao período de cinco anos de cultivo, aplicou-se adubação corretiva de P à superfície do solo, com 0,0 ou 80,0 kg ha-1 P2O5, nas formas de superfosfato triplo ou fosfato Arad. Após esse período de cinco anos, as parcelas receberam a mesma adubação corretiva de antes, e a braquiária foi introduzida no sistema de cultivo no lugar das outras plantas de cobertura. Após o cultivo da braquiária, foram coletadas amostras de solo, na camada 0-10 cm, e submetidas ao fracionamento de P. A soja foi cultivada em seguida, sem adubação fosfatada no sulco de plantio. A disponibilidade de P nas parcelas com a braquiária foi comparada àquelas com vegetação espontânea, por dois anos. O cultivo da braquiária aumentou os teores de P inorgânico (extraído com resina) e orgânico (NaHCO3) no solo, bem como o conteúdo de P nas folhas da soja, independentemente da fonte de P utilizada. No entanto, a produtividade da soja não aumentou significativamente pela introdução da braquiária ao sistema de cultivo. A braquiária aumenta a disponibilidade de P no solo, especialmente nas áreas com adubação fosfatada corretiva.

The objective of this work was to evaluate the effectiveness of ruzigrass (Urochloaruziziensis) in enhancing soil-P availability in areas fertilized with soluble or reactive rock phosphates. The area had been cropped for five years under no-till, in a system involving soybean, triticale/black-oat, and pearl millet. Previously to the five-year cultivation period, corrective phosphorus fertilization was applied once on soil surface, at 0.0 and 80 kg ha-1 P2O5, as triple superphosphate or Arad rock phosphate. After this five-year period, plots received the same corrective P fertilization as before and ruzigrass was introduced to the cropping system in the stead of the other cover crops. Soil samples were taken (0-10 cm) after ruzigrass cultivation and subjected to soil-P fractionation. Soybean was grown thereafter without P application to seed furrow. Phosphorus availability in plots with ruzigrass was compared to the ones with spontaneous vegetation for two years. Ruzigrass cultivation increased inorganic (resin-extracted) and organic (NaHCO3) soil P, as well as P concentration in soybean leaves, regardless of the P source. However, soybean yield did not increase significantly due to ruzigrass introduction to the cropping system. Soil-P availability did not differ between soluble and reactive P sources. Ruzigrass increases soil-P availability, especially where corrective P fertilization is performed.

An adequate supply of boron (B) is required for the optimal growth and development of cotton (Gossypium hirsutum L.) plants, but the low phloem mobility of B limits the possibilities of correcting B deficiency. There are indications that different cotton cultivars could have different responses to B deficiency. The differences in responses of cotton cultivars to B regarding photoassimilate production and transport were studied in a greenhouse experiment with nutrient solution. Treatments consisted of three cotton cultivars (FMT 701, DP 604BG and FMX 993) and five concentrations of B (0.0, 2.5, 5.0, 10.0 and 20.0 µmol L−1). Sampling began at the phenological stage B1 (first square) and continued for four weeks. The leaf area and the number of reproductive branches and structures decreased due to B deficiency. A higher level of abortion of reproductive structures was observed under B deficiency. Boron deficiency increased the internal CO2 concentration but decreased the transpiration rate, stomatal conductance and photosynthesis. Despite the decrease in photosynthesis, nonstructural carbohydrates accumulated in the leaves due to decreased export to bolls in B-deficient plants. The response to B deficiency is similar among cotton cultivars, which shows that the variability for this trait is low even for cultivars with different genetic backgrounds.

A deficiência de fósforo (P) é um dos principais fatores limitantes da produtividade em solos tropicais, mas há indicações de que algumas plantas podem melhorar a disponibilidade do P no solo. O trabalho teve por objetivo avaliar as transformações do P durante o cultivo da braquiária e do tremoço-branco, além de um possível aumento de formas orgânicas de P no solo. O experimento foi instalado em casa de vegetação, onde foram cultivados braquiária (Urochloa ruziziensis) e tremoço branco (Lupinus albus L.), fertilizados com 0; 20; 40; 60 e 80mg dm-3 de P. As plantas foram cultivadas por 60 dias. A adubação com P aumentou a produção de matéria seca da braquiária e tremoço branco. O P bioativo (extraído com EDTA) é aumentado pelas doses de P, mas não é afetado pelas espécies vegetais. O tremoço branco é mais eficiente em absorver o P, enquanto a braquiária é mais eficiente em reduzir a capacidade máxima de adsorção de P do solo.

Phosphorus is one of the major factor that limits agricultural productivity in most tropical soils. The objective of this study was to assess P transformations and availability in a soil cropped to brachiaria (Urochloa ruziziensis) and white lupin (Lupinus albus L.). The study was carried out in a greenhouse at Botucatu, State of São Paulo, Brazil. Brachiaria and white lupin were grown in pots with soil fertilized with 0, 20, 40, 60 and 80mg dm-3 P. The plants were grown for 60 days, when they were harvested and the soil was sampled. Dry matter yields of both species were increased with P rates. Soil bioactive P is increased with P fertilization, but is not affected by the plant species. White lupin is more effective in taking up the organic soil P, but Brachiaria was more effective in reducing the soil maximum P adsorption capacity.