ABSTRACT. Phosphorus (P) is one of the most important elements used in fertilizing soils in tropical regions due to the low efficiency of phosphate fertilization. This work aimed to fractionate inorganic P (Pi) in tropical soils of different mineralogical compositions and to relate these fractions with their respective phosphate buffer capacity (PBC) indicators. The soils were characterized physically, chemically and mineralogically. Additionally, we evaluated the P concentration that remained in solution of soil after equilibrium was met; this was termed P remaining (P-rem). In general, the Pi fractions of soils did not correlate with the PBC indicators. The P-H2O fraction showed a negative correlation with the P-Al fraction. Ferric minerals did not influence P fixation. P-rem showed a strong correlation with the maximum P adsorption capacity, adsorption energy, and the amorphous and crystalline forms of Fe. The minerals of aluminum contributed the most to P fixation. P-rem was the best estimator of PBC. The soils with high, moderate and low rates of P fixation showed high amounts of the fractions P-Al, P-Ca, and P-Fe, respectively. The results showed that P fixation was influenced by the fractions of P in the soil, suggesting that the efficiency of phosphate fertilizers in tropical soils depends on the mineralogy of the clay fraction within those soils.

RESUMO A fosfatagem aumenta os teores de fósforo (P) na camada superficial do solo, estimula o crescimento das raízes das plantas e aumenta o volume de solo explorado para absorção de água e nutrientes, o que pode reduzir o estresse oxidativo abiótico na cana-de-açúcar. O objetivo deste trabalho foi avaliar a produtividade e a resposta do sistema enzimático antioxidante da cana-de-açúcar quando cultivada em solo que recebeu a fosfatagem corretiva, utilizando doses e fontes de P com solubilidade variada. O experimento foi conduzido em condições de campo na Zona da Mata Sul do Estado de Pernambuco, Brasil. Os tratamentos foram dispostos no delineamento de blocos casualizado, em esquema fatorial (4 × 3) +1, com quatro repetições. Os fatores foram constituídos do controle (sem fosfatagem), pelas doses (50, 100, 200 e 300 kg ha-1 de P2O5) e fontes (fosfato natural reativo, superfosfato triplo e torta de filtro) de P aplicadas em área total, no pré-plantio do ciclo de cana planta. O teor de P nos tecidos da folha foi considerado adequado e não foi influenciado pela prática da fosfatagem. A fosfatagem com a dose estimada de 150 kg ha-1 de P2O5 reduziu a atividade das enzimas antioxidantes e aumentou em 25,0% a biomassa seca da parte aérea (MSPA) e em 8,5% a produtividade de colmos. A superóxido dismutase (SOD) apresentou o maior coeficiente de correlação positivo com as demais enzimas antioxidantes e negativo com a MSPA, podendo ser utilizada para avaliar estresse abiótico que promoveu a redução na produtividade na cana-de-açúcar.

ABSTRACT Corrective phosphate application increases the levels of phosphorus (P) in the surface layer of the soil, stimulates plant root growth and increases the volume of soil exploited for water and nutrient uptake, which may reduce abiotic oxidative stress in sugarcane. The aim of this study was to evaluate the productivity and the response of the antioxidant enzyme system in sugarcane when grown in soil that received corrective phosphate application, using doses and sources of P of varying solubility. The experiment was conducted under field conditions in the southern Forest Zone of the State of Pernambuco, Brazil. The treatments were arranged in a randomised block design, in a (4 × 3) +1 factorial scheme with four replications. The factors consisted of a control (with no phosphate application) and the doses (50, 100, 200 and 300 kg P2O5 ha-1 ) and sources (reactive natural phosphate, triple superphosphate and sugarcane press mud) of P applied during the pre-planting stage of the plant cane cycle. The P content of the leaf tissue was considered adequate, and was not influenced by the phosphate application. Phosphate application at an estimated dose of 150 kg P2O5 ha-1 reduced antioxidant enzyme activity and increased shoot dry matter (SDM) by 25.0% and stalk productivity by 8.5%. Superoxide dismutase (SOD) showed the highest positive correlation coefficient with the other antioxidant enzymes, and a negative correlation with SDM, and can be used to evaluate abiotic stress that promotes reductions in sugarcane productivity.

ABSTRACT Prior research on sugarcane showed increment of productivity following molybdenum (Mo) fertilization and some indication of the potential role either on nitrate reductase activity (NRA). However, this increment can depend on sugarcane variety and nitrogen (N) fertilization. This study aimed to evaluate the effect of Mo fertilization on Mo uptake, on NRA, nitrate (NO3--N), and ammonium (NH4+-N) contents in leaves and roots of sugarcane, and the accumulation of N and biomass across two sugarcane varieties (RB 867515 and RB 92579). The varieties were subjected to two rates of N fertilization (without N fertilization and 60 kg ha-1 of N) and two rates of Mo fertilization (without Mo fertilization and 200 g ha-1 of Mo). At 70, 100, 130, 200, and 365 days after planting (DAP), the following parameters were determined: Mo, NO3--N and NH4+-N contents, NRA in the leaves and roots, and the accumulation of N, as well as shoot dry matter (SDM). Molybdenum fertilization increased N accumulation in 36 and 44 % in the varieties RB 867515 and RB 92579, respectively. This increase in N accumulation was associated with NRA stimulation of 13 % in the leaves and 42 % in the roots. The maximum NRA occurred around 100 DAP, and its contents in the leaves and roots of the RB 92579 were 0.83 and 0.46 µmol NO2- g-1 h-1 of fresh matter, respectively, and in RB 867515 these values were 0.61 and 0.43 µmol NO2- g-1 h-1 of fresh matter, respectively. The assimilation of NO3--N was increased with Mo application, both with and without N fertilization, suggesting that Mo fertilization is indicated in nutrition management of sugarcane. This study provides insight into how Mo fertilization interacts with N fertilization and sugarcane varieties, altering N accumulation and dry matter production.

ABSTRACT Micronutrient research for sugarcane in northeastern Brazil is scarce and most works on this issue date back to the 70’s and 80’s. The objectives of this study were to assess the available and reserve pools of Fe, Mn, Cu, and Zn in soils cultivated with sugarcane under three geological contexts in northeastern Brazil as well as to diagnose the micronutrient nutritional status of sugarcane grown on these areas in order to identify pedogeological conditions in which micronutrient deficiencies are likely. Results showed that the soils cultivated with sugarcane in the states of Paraíba and Pernambuco posed available and reserve contents of micronutrients related to the parent materials and soil textural classes. The reserve contents of Fe, Mn, Zn, and Cu in all the soil samples analyzed were below the background values established for the region, which indicates a continuous exportation of micronutrients through cultivation. The mean and median contents of Mn, Zn, and Cu in diagnostic leaves of sugarcane were below their respective nutritional optimum ranges recommended to Brazil while Fe contents achieved the crop nutritional requirement. This is the first time such an approach based on pedogeological contexts is used to study the available and reserve pools of micronutrients in soils of Northeast Brazil.

Abstract: The increase of N fertilization in sugarcane can negatively influence the technological quality of the crop for sugar and alcohol production. The use of Mo in fertilization combined with N can reduce this effect and increase agricultural and sugar yield. The objective of this study was to evaluate the levels of Mo in soil, roots and leaves of sugarcane fertilized with N and Mo, to measure agricultural and sugar productivity and to evaluate quality of the technological attributes for production of sugar and alcohol. Two varieties were cultivated (RB867515 and RB92579) under field conditions, submitted to two doses of N (0 and 60 kg ha-1) and two doses of Mo (0 and 200 g ha-1) both applied to the soil. The source of N used was urea and the source of Mo was sodium molybdate. RB867515 was influenced by Mo and agricultural and sugar productivity increased by 21%. N fertilization did not increase agricultural productivity but reduced the technological quality of sugarcane, and Mo did not change this reduction. It is suggested that N fertilization should be reduced in first crop cycle and Mo fertilization should be stimulated.

O objetivo deste trabalho foi avaliar a disponibilidade de P em solos representativos para o cultivo da cana-planta no Nordeste brasileiro, e estabelecer uma nova recomendação de adubação com o nutriente para a cultura nestes solos. O estudo foi realizado em cinco solos da Zona da Mata de Pernambuco: Argissolo Amarelo distrocoeso, Argissolo Amarelo distrófico, Latossolo Amarelo distrófico, Gleissolo Háplico eutrófico e Espodossolo Humilúvico órtico. Avaliaram-se sete doses de P, determinadas quanto à capacidade máxima de adsorção de P de cada solo (fósforo remanescente, P-rem). Aos 30 dias após a fertilização, os teores de P nos solos foram determinados com os extratores Mehlich-1, Mehlich-3, Bray-1 e resina de troca aniônica. Os níveis críticos de P foram calculados para cada solo e extrator. A partir dos intervalos de disponibilidade de P, foram definidas cinco classes de fertilidade para diferentes conteúdos de argila nos solos: muito baixa, baixa, média, alta e muito alta. Mehlich-1 e a resina de troca aniônica são os extratores capazes de representar adequadamente a disponibilidade P, para o cultivo de cana-planta nos solos avaliados.

The objective of this work was to evaluate P availability in representative soils for plant cane cultivation in the Brazilian Northeast region, and to establish a new P-fertilizing recommendation for this crop in these soils. The study was done in five soil types, in Zona da Mata of Pernambuco: Argissolo Amarelo distrocoeso (Ultisol), Argissolo Amarelo distrófico (Ultisol), Latossolo Amarelo distrófico (Oxisol), Gleissolo Háplico eutrófico (Gleisol), and Espodossolo Humilúvico órtico (Spodosol). Seven P doses were evaluated for maximum P adsorption capacity of each soil (solution equilibrium phosphorus, P-rem). Thirty days after soil fertilization, P contents in soils were determined with the extractors Mehlich-1, Mehlich-3, Bray-1, and anion exchange resin. P critical levels were calculated for each soil and extractor. From P availability ranges, five fertility classes were defined for different clay contents in the soils: very low, low, medium, high, and very high. Mehlich-1 and anion exchange resin are able extractors to adequately represent soil-P availability for plant cane cultivation in the evaluated soils.

O objetivo deste trabalho foi avaliar no ciclo de cana planta a capacidade de onze variedades de cana-de-açúcar (SP79-1011; RB813804; RB863129; RB872552; RB943365; RB72454; RB763710; SP78-4764; SP81-3250; RB867515 e RB92579), cultivadas sob irrigação plena, em acumular os nutrientes N, P, K, Ca e Mg nos componentes da parte aérea (colmo, folha e ponteiro). A pesquisa foi realizada em condições de campo, no município de Carpina/PE, na safra agrícola 2006/2007. O delineamento experimental empregado foi de blocos casualizados com quatro repetições. O acúmulo de nutrientes nos componentes da parte aérea foi avaliado aos 120; 180; 240; 300 e 360 dias após o plantio (DAP). Observou-se no ciclo da cana-de-açúcar, remobilização dos nutrientes N, P e K das folhas para os ponteiros e colmos. Aos 360 DAP o acúmulo de N, P e K na parte aérea mostrou-se superior à quantidade adicionada via fertilizantes. As variedades RB92579 e SP81-3250 se destacaram pelo maior acúmulo de nutrientes nos colmos, enquanto a RB867515 e RB943365 foram as variedades que mais alocaram nutrientes na folha, o que as identifica como variedades de maior capacidade de ciclagem de nutrientes.

The objective of this study was to evaluate, along the first cycle of sugar cane, the capacity of eleven varieties of sugar cane (SP79-1011; RB813804; RB863129; RB872552; RB943365; RB72454; RB763710; SP78-4764; SP81-3250; RB867515 and RB92579), cultivated under full irrigation,the accumulation of the nutrients N, P, K, Ca and Mg in the plants aerial parts (stem, leaf and pointer). The research was carried through under field conditions, during the agricultural season 2006/2007, in the Sugar Cane Agricultural Station of the Federal Rural University of Pernambuco, in Carpina County, PE/Brazil. The experimental set was a complete randomized block design, with four replications. The accumulation of nutrients in the components of the aerial part was evaluated at 120; 180; 240; 300 and 360 days after plant (DAP). It was observed along the cycle of the sugar cane, mobilization of nutrients N, P and K from the leaves to the points and stems. At 360 DAP the accumulation of N, P and K in the aerial part was higher than the amount added by fertilizers. The varieties RB92579 and SP81-3250 were detached by the highest nutrients accumulation in stems, while RB867515 and RB943365 were the varieties that allocated more nutrients in leaf, which identifies them as the varieties of larger capacity of cycling of those nutrients.

O objetivo deste trabalho foi avaliar a produtividade de colmos e de açúcar, a eficiência de uso da água e os atributos tecnológicos de cinco variedades de cana-de-açúcar de maturação precoce e seis de maturação média à tardia, submetidas ao regime de sequeiro (1.141,4 mm) e à irrigação plena (1.396,6 mm). Utilizou-se o delineamento experimental de blocos ao acaso, com quatro repetições. A produtividade de colmos das variedades RB92579, RB72454 e SP81-3250 apresentou ganhos superiores a 180%, com uso da irrigação. A irrigação promoveu aumentos na produtividade de açúcar superiores a 200%, nas variedades RB92579 e RB943365. A irrigação plena proporcionou maior eficiência de uso da água, com produção média de 70,2 kg ha-1 mm-1 de colmos a mais em comparação ao regime de sequeiro. Com exceção das variedades RB72454, RB763710 e RB943365, não houve diferença nos atributos tecnológicos entre a irrigação plena e o regime de sequeiro. As variedades RB92579 e SP81-3250 de maturação média à tardia se destacam quanto à produtividade de colmos e de açúcar e à eficiência de uso da água, e são recomendadas para estudos de resposta à irrigação pela cana-de-açúcar.

The objective of this work was to assess stalk and sugar yield, water use efficiency, and technological attributes of five early maturing and six medium to late maturing sugarcane varieties with no irrigation (1,141.4 mm) and under full irrigation (1,396.6 mm). A randomized complete block design, with four replicates, was used. Stalk yield for varieties RB92579, RB72454, and SP81-3250 showed gains above 180% with irrigation. Irrigation increased sugar yield in more than 200% in the RB92579 and RB943365 varieties. Full irrigation provided greater water use efficiency, producing, in average, 70.2 kg ha-1 mm-1 more stalks than under no irrigation. Except for the varieties RB72454, RB763710, and RB943365, there were no differences regarding technological attributes between full irrigation and no irrigation. The medium to late maturing varieties RB92579 and SP81‑3250 have higher stalk and sugar yield and better water use efficiency, and are recommended for studies on sugarcane response to irrigation.

A pesquisa tecnológica para suporte do setor sucroalcooleiro nacional mostra que são esporádicos os trabalhos desenvolvidos com cana-de-açúcar irrigada envolvendo a exigência nutricional. Nesse contexto, objetivou-se quantificar, durante o ciclo de cana-planta de 11 variedades de cana-de-açúcar (SP79-1011, RB813804, RB863129, RB872552, RB943365, RB72454, RB763710, SP78-4764, SP81-3250, RB867515 e RB92579) cultivadas sob irrigação plena, a capacidade de extração e exportação de N, P, K, Ca e Mg, bem como a exigência nutricional para produção de uma tonelada de colmo por hectare (TCH). A pesquisa foi realizada em campo, no município de Carpina, PE, durante a safra agrícola 2006/2007. O delineamento experimental empregado foi de blocos casualizados, com 11 tratamentos e quatro repetições. A extração e exportação de nutrientes, assim como a exigência nutricional, foram avaliadas aos 360 dias após o plantio (DAP) na parte aérea das plantas. A extração de nutrientes na parte aérea da cana-planta apresentou, em média, valores de 179, 25, 325, 226 e 87 kg ha-1 de N, P, K, Ca e Mg, respectivamente, o que proporcionou a seguinte ordem decrescente de extração: K > Ca > N > Mg > P. A exportação média de N, P, K, Ca e Mg pelo colmo das variedades irrigadas foi de 92; 15; 188; 187; e 66 kg ha-1; correspondendo, respectivamente, a 51, 60, 58, 83 e 76 % de todo o nutriente extraído na parte aérea da cana-planta, com destaque para as variedades RB92579 e SP81-3250 para o N, RB813804, RB863129, RB872552, RB763710, RB92579, SP78-4764, SP81-3250 e SP79-1011 para o P, SP79-1011, SP81-3250, RB813804, RB872552 e RB763710 para o K, RB92579 e RB863129 para o Ca e RB92579 para o Mg. Para produção de uma TCH, foram exigidos pelas variedades durante o ciclo de cana-planta valores médios de 0,91; 0,13; 1,71; 1,18; e 0,44 kg de N, P, K, Ca e Mg, respectivamente.

A review of technology research supporting the Brazilian sugaralcohol sector shows that only sporadic studies with irrigated sugarcane have been developed to investigate nutritional requirements. In this context, the objective of this study was to quantify the capacity of extraction and export of N, P, K, Ca, and Mg as well as the nutritional requirement for the production of one ton of stalk per hectare (TCH) in the plant cane cycle of 11 sugarcane varieties (SP79-1011, RB813804, RB863129, RB872552, RB943365, RB72454, RB763710, SP78-4764, SP81-3250, RB867515, and RB92579) grown under full irrigation. The research was conducted under field conditions in the municipality of Carpina, PE, in the 2006/2007 growing season. The experiment was arranged in a randomized block design with 11 treatments and four replications. Nutrient extraction and export as well as nutritional requirements of the shoot components of the plants were evaluated 360 days after planting. The mean nutrient accumulation in shoots was 179, 25, 325, 226, and 87 kg ha-1 of N, P, K, Ca, and Mg, respectively.The average export of N, P, K, Ca, and Mg via stalks of the irrigated varieties was 92, 15, 188, 187, and 66 kg ha-1; corresponding, respectively, to 51, 60, 58, 83, and 76 % of the whole nutrient amount taken up by the cane plant. The extracted nutrient amounts were highest by the following varieties: RB92579 and SP81-3250 for N; RB813804, RB863129, RB872552, RB763710, RB92579 SP78-4764, SP81-3250 and SP79-1011 for P; SP79-1011, SP81-3250, RB813804, RB872552 and RB763710 for K; RB92579 and RB863129 for Ca; and RB92579 for Mg, for which the export values in stalks were highest. For the production of one TCH, the varieties needed 0.91, 0.13, 1.71, 1.18, and 0.44 kg of N, P, K, Ca, and Mg, respectively.