ABSTRACT Studies aimed at mitigating environmental impacts have received attention in recent years. The use of biochar obtained from the pyrolysis is an alternative for the recovery of organic materials that usually are directly discarded in the environment. Biochar has the potential to recover nutrients from wastewater, and in the latter case, the reuse or recycling of biochar as a controlled-release fertilizer could be an option. However, the adsorption characteristics of the ions into different biochars have not been known. The aim of this study was to evaluate the ions adsorption in biochar derived from discarded potatoes, as well as to make physical and chemical characterization of the produced materials. The biochar derived from discarded potatoes was produced by pyrolysis at 450 °C under an N2 atmosphere. In order to define its ionic profile, the adsorption of HnPO4(3–n)–, Ca2+, Mg2+, and Al3+ was tested in pure biochar, as well as adsorption of HnPO4(3–n)–in biochar after it was doped with Al3+. The desorption of these ions was tested by washing with deionized water, and the KCl (1.0 mol·L–1) and Mehlich-1 extractors. In absolute values, the adsorption order of the ions was Al3+ (in acid pH value) = Ca2+ > Al3+ > HnPO4(3–n)–(biochar doped with Al3+) > Mg2+ > HnPO4(3–n)– (biochar without doping). The adsorption of HnPO4(3–n)– was positively influenced by the doping of biochar with Al3+. The biochar has preferential characteristics for cations adsorption, and the doping process can aid in adsorption of anions.

RESUMO A eficiência da adubação fosfatada pode ser reduzida pela incorporação do fertilizante ao solo com enxada rotativa, método que é comumente adotado no cultivo de hortaliças. Objetivou-se avaliar a produtividade de repolho e a eficiência de adubação fosfatada, em função de doses e modos de aplicação de P ao solo. Foram conduzidos quatro experimentos [dois com aplicação a lanço (0 kg ha-1, 200 kg ha-1, 400 kg ha-1, 800 kg ha-1 e 1.600 kg ha-1 de P2O5) e dois com aplicação localizada (0 kg ha-1, 80 kg ha-1, 160 kg ha-1, 320 kg ha-1 e 640 kg ha-1 de P2O5, combinados com a presença ou ausência de fosfatagem - aplicação a lanço de 200 kg ha-1 de P2O5)], em dois locais de cultivo [solo de menor (A) e maior (B) disponibilidade de P, ambos de textura muito argilosa]. As doses de 252 kg ha-1 e 284 kg ha-1 de P2O5 foram estimadas para a obtenção da máxima produtividade econômica com a aplicação a lanço nos locais A e B, respectivamente. As melhores doses foram 183 kg ha-1 e 146 kg ha-1 de P2O5 com a aplicação localizada de P sem fosfatagem nos locais A e B, respectivamente. A eficiência de recuperação para a obtenção de 95 % da máxima produtividade foi de 48,9 % e 30,0 % nos locais A e B, respectivamente. Para o P aplicado localizado na ausência de fosfatagem, estes índices foram de 44,6 % e 60,4 % nos locais A e B, respectivamente. Com a fosfatagem, a eficiência de recuperação diminui de forma significativa. A aplicação localizada de P é mais eficiente que a aplicação a lanço no fornecimento de nutrientes e para a produtividade de repolho.

ABSTRACT The efficiency of phosphate fertilization may be reduced by incorporating the fertilizer to the soil using a rotary tiller, which is a method commonly adopted to grow vegetables. This study aimed to evaluate the yield of cabbage crop and the efficiency of phosphate fertilization based on rates and application methods of P to the soil. Four experiments were carried out [two using broadcasting application (0 kg ha-1, 200 kg ha-1, 400 kg ha-1, 800 kg ha-1 and 1,600 kg ha-1 of P2O5) and two using localized application (0 kg ha-1, 80 kg ha-1, 160 kg ha-1, 320 kg ha-1 and 640 kg ha-1 of P2O5, combined with the presence or absence of phosphating - application of 200 kg ha-1 of P2O5 by broadcasting)] in two growing sites [one with low (A) and another with high (B) content of P, both showing a very clayey texture]. The rates of 252 kg ha-1 and 284 kg ha-1 of P2O5 were estimated to obtain the maximum economic productivity in the broadcasting application at the sites A and B, respectively. The best rates were 183 kg ha-1 and 146 kg ha-1 of P2O5 with the localized application of P without phosphating at the sites A and B, respectively. To obain 95 % of maximum yield, the recovery efficiency was 48.9 % and 30.0 % at the sites A and B, respectively. For the localized application of P in the absence of phosphating, these values were 44.6 % and 60.4 % at the sites A and B, respectively. With phosphating, the recovery efficiency decreased significantly. The localized application of P is more efficient than the broadcasting application to supply nutrients and increase the cabbage yield.

RESUMO A cenoura está entre as principais olerícolas consumidas no Brasil, onde as cultivares utilizadas atualmente apresentam elevado potencial produtivo e demanda nutricional, o que exige constantes ajustes dos programas de fertilização da cultura. Objetivou-se determinar valores de referência e índices diagnósticos pelo método DRIS para três fases fenológicas da cultura da cenoura (cerca de 40 e 70 dias após a semeadura e na colheita), bem como verificar a possibilidade de diagnose precoce de limitação nutricional. Para determinação das normas DRIS, obteve-se um banco de dados a partir da amostragem de folhas, produtividade de raízes e teores foliares de N, P, K, Ca, Mg, S, B, Cu, Mn e Zn, em lavouras comerciais de cenoura. A ordem de limitação nutricional foi gerada em função do potencial de resposta à adubação e da faixa ótima dos teores foliares. Os valores referência de K, Ca, Mg, S e Mn mostraram-se semelhantes em todas épocas de amostragem. Os de N, P, B, Cu e Zn variaram, reforçando a ideia de padronização da época de amostragem para esses nutrientes. O Mn, K e Mg foram os nutrientes mais limitantes por deficiência, enquanto Zn e B foram os menos limitantes. Para K, Ca, Mg, S e Mn, há concordância entre a diagnose realizada nas fases precoces e a efetuada na colheita, o que indica possibilidade de diagnose precoce da limitação desses nutrientes.

ABSTRACT Carrot is one of the most consumed vegetables in Brazil, where the cultivars currently grown present a high yield potential and nutritional demand, which require constant adjustments in fertilization programs for the crop. This study aimed at determining reference values and diagnostic indices by using the DRIS method in three phenological stages of the carrot crop (around 40 and 70 days after sowing and at harvest), as well as evaluating the possibility of early diagnosis for nutritional limitations. For determining the DRIS norms, a database was obtained from leaf samplings, root yields and leaf contents of N, P, K, Ca, Mg, S, B, Cu, Mn and Zn, in carrot commercial fields. The nutritional limitation order was generated as a function of the fertilization response and optimum range of leaf contents. The reference values for K, Ca, Mg, S and Mn were similar in all sampling times. N, P, B, Cu and Zn varied with the stages sampled, indicating the need to standardize the sampling times for these nutrients. Mn, K and Mg were the most limiting nutrients for the crop growth, while Zn and B were the least limiting. There was a correlation between the diagnoses performed at early stages and those performed at harvest for K, Ca, Mg, S and Mn, indicating the possibility of early diagnosis for the deficiency of these nutrients.