B. van Raij

Extraction of boron from soil by microwave heating for ICP‐AES determination

Abstract Extraction with hot water is the most widely used procedure to determine boron (B) in soils for the diagnosis of the nutrient availability for plants. However, this procedure is tedious for routine conditions and requires some special precautions. An alternative extraction procedure was developed, consisting in the extraction of B with a 1.25 g/L solution of barium chloride (BaCl2) or with water heated in a domestic microwave oven. Boron was determined either by inductively coupled argon plasma emission spectrometry (ICP‐AES) and by spectrophotometry with azomethine‐H. Good correlations were found between the extraction by boiling water under reflux and the extraction by the microwave heating for 13 Brazilian soils, and the contents of B obtained by spectrophotometry did not differ significantly from those obtained by ICP‐AES. Considering the calculated standard deviations, it can be concluded that microwave heating followed by ICP‐AES determination is an adequate procedure for the determination ...

PHOSPHORUS AND POTASSIUM SOIL TEST AND NITROGEN LEAF ANALYSIS AS A BASE FOR CITRUS FERTILIZATION

A network of six NPK long-term field trials was carried out on different soils of citrus-producing regions of São Paulo state, Brazil, in order to estimate quantitative relations of fruit yield to NPK fertilization and to determine parameters for fertilizer recommendation based on soil testing and leaf analysis. The experiments were set up in an incomplete factorial design 1/2 43 with 32 treatments, with four yearly rates of N (30, 100, 170 and 240 kg N/ha), P (9, 27, 45 and 63 kg P/ha) and K (25, 91, 157 and 223 kg K/ha). Four to seven harvests were recorded for the six experiments. Response surfaces of the type y = bo + b1N + b11N2 + b2P + b22P2 + b3K + b33K2 + b12NP + b13NK + b23PK were adjusted to the average yields of each trial. Correlation were established for yield increases, expressed as relative yields, and results of soil analysis of P and K, and leaf analysis of N. Soil samples taken at 0-20 cm depth in the beginning of each experiment were analyzed for resin extractable P and exchangeable K using an ion-exchange resin procedure. Yield responses for phosphorus and potassium applications were observed respectively in soils with less than 20 mg dm-3 of P and 20 mmolc dm-3 of K+. Yield responses to nitrogen were related to the total content of nitrogen in leaves, being largest for N values of 23 g kg-1 and smallest for N of 28 kg-1. With these field information, a practical approach for fertilizer recommendation for citrus, based on soil analysis for P and K and leaf analysis for N, was developed.

Soil and plant analyses for lime and fertilizer recommendations in Brazil

Abstract The fertilizer recommendation guidelines for over 160 crops for the State of Sao Paulo, Brazil were updated in 1996 based on recent results of research on soil and plant analysis, and crop responses. Recommendations are based mainly on soil analysis and expected yield. Limestone rates are calculated to raise soil base saturation as a percentage of the cation exchange capacity (CEC) of the soil at pH 7.0, to levels which vary with crop species (i.e., to 50% for rice, coffee, and cassava, 60% for sugar cane and soybeans, 70% for cotton and maize, and 80% for grapes and onions). In addition, exchangeable magnesium (Mg) contents must reach a minimum level. Exchangeable subsoil aluminum (Al) and calcium (Ca), and clay content are used to determine rates of gypsum as amendment of subsoil acidity. Fairly consistent data on soil phosphorus (P) and potassium (K) calibration are available for Brazilian soils. Potassium rates are recommended based on values of soil exchangeable K and, for P fertilization, i...

Efficiency of multinutrient extractants for the determination of available copper in soils

Abstract Experiments under greenhouse conditions were carried out at the Instituto Agronomico de Campinas in order to determine the efficiency of some multinutrient extradants on the determination of available copper in soils from the State of Sao Paulo, Brazil. These experiments employed 31 soils using wheat and beans as test plants. All soil samples were limed to increase the soil pH to 6.0 and manured with copper‐free fertilizer. Copper was extracted from the soils before liming and before each planting using the Mehlich‐1, Mehlich‐3, or the TEA‐DTPA as extracting reagents followed by its determination using the inductively coupled plasma emission spectrometry (ICP‐AES) technique. The wheat and beans plants were also analysed for their copper content. The results showed that the extraction of the available copper decreased in the order: Mehlich‐3, TEA‐DTPA and Mehlich‐1. The Mehlich‐3 (R2 = 0.80**) and the TEA‐DTPA (R2 = 0.74**) methods explained well the variation in the copper concentration found in ...

Gesso na produção de cultivares de milho com tolerância diferencial a alumínio em três níveis de calagem

O gesso, nos ultimos anos, vem sendo considerado como um insumo capaz de melhorar o ambiente radicular de subsolos acidos. Contudo, ainda pairam duvidas sobre a vantagem de usa-lo em solos que, embora acidos, tenham sido submetidos a calagens e adubacoes anteriores. Tambem ha pouca informacao sobre o uso de gesso em presenca de aplicacoes elevadas de calcario ou em plantas cultivadas tolerantes a acidez. No presente trabalho, e relatado experimento com calcario e gesso, realizado, de 1987 a 1992, na Estacao Experimental de Tatui (SP), em Latossolo Vermelho-Escuro alico textura argilosa, com o objetivo de avaliar o efeito de calcario e de gesso nas producoes de cultivares de milho tolerante ou susceptivel a aluminio, bem como o efeito dos corretivos na acidez do solo. O experimento foi instalado em parcelas subsubdivididas, com quatro repeticoes, em blocos ao acaso. Nas parcelas principais, foram aplicadas 0, 6 ou 12 t ha-1 de calcario dolomitico e, nas subparcelas, 0, 4 e 8 t ha-1 de fosfogesso; nas subsubparcelas, foram plantados dois cultivares, um sensivel e outro tolerante a aluminio. Para as quatro colheitas obtidas (os dados de 1990 foram considerados perdidos), percebeu-se efeito significativo para a calagem nos dois tipos de cultivares. O gesso apresentou efeito significativo nas producoes apenas para o cultivar sensivel ao aluminio e, nesse caso, o efeito foi aditivo ao de calcario, proporcionando, em media, cerca da metade do aumento de producao devida a calagem. A calagem influenciou, consideravelmente, a reacao da camada aravel do solo, aumentando o pH, os teores de Ca2+ e Mg2+ e reduzindo a acidez potencial, mas pouco influiu nas camadas mais profundas, o que, provavelmente, se deveu ao fato de o solo ter recebido aplicacoes anteriores de calcario e de adubos com sulfato. O gesso influiu nos teores de Ca2+ e SO42- em profundidade, embora de forma pouco pronunciada em relacao as quantidades aplicadas, e nao alterou as caracteristicas de acidez. Pode-se concluir que, mesmo tendo alterado pouco as caracteristicas quimicas do subsolo, o gesso favoreceu a producao de cultivar de milho sensivel a acidez.

Revisiting titration procedures for the determination of exchangeable acidity and exchangeable aluminum in soils

Abstract The use of 1 mol L‐1 ammonium chloride (NH4Cl) or ammonium nitrate (NH4NO3) solutions as alternative soil extractants were evaluated for the determination of the exchangeable acidity and exchangeable aluminum (Al) in twelve soil samples by the traditional titration/back‐titration method. The exchangeable Al results were compared with those obtained by inductively coupled plasma emission spectrometry (ICP‐AES) measurements while the exchangeable acidity results, using either NH4Cl or NH4NO3 solutions as alternative soil extractants, were compared against those using 1 mol L‐1 potassium chloride (KCl) and bromothymol blue as the indicator. The results indicated that the use of ammonium (NH4) salts in these determinations is not recommended since the exchangeable acidity found using these extractants was systematically higher than that found in KCl extracts due to the additional acidity caused by the presence of comparatively higher concentrations of NH4 + ions. In addition, the reaction media also ...

Plant availability of phosphorus in the neutral ammonium citrate fraction of Brazilian acidulated phosphates

In Brazil, where the rock phosphates are high in impurities, no attempthas been made to evaluate the P supplying efficiency of the neutral ammoniumcitrate fraction (NAC) of P fertilizers, or to verify if the NAC +H2O extraction solution (AOAC) is satisfactory for estimatingthe P availability. To attain these objectives, a greenhouse experiment wascarried out with samples of a Typic Hapludox soil. Four acidulatedphosphates obtained from Brazilian raw materials were studied; monocalciumphosphate p.a.[Ca(H2PO4)2·H2O]was included as a standard source of P, as well as leached samplescontaining no water-soluble P. The fertilizers were thoroughly mixed withthe whole soil in the pots or with only 1% of its volume, at the rateof 50 mg kg-1 of P, soluble in NAC + H2O. Cornplants (Zea mays, L.) were grown for 35 days and the amounts of dry matterand P accumulated in plant tops were determined. Increasing the amount ofcationic impurities in the raw materials decreased the concentration ofwater-soluble P, NAC + H2O-soluble P and water-soluble P/NAC+H2O soluble P ratio of the fertilizers obtained. The P in theNAC fraction was not as much available to plants as in the NAC +H2O fraction or in pure MCP. The great variation found in drymatter (5.4 to 17.1 g pot-1) and in P uptake (6.3 to 22.2 mgpot-1) indicates that the AOAC method is not an adequate indexfor evaluating the P availability of fertilizers with high amounts ofcationic impurities.

Lime effect on soil N availability indexes as measured by plant uptake

Abstract Lime application to acid soils usually increases N mineralization but little is known about how it affects the N determined by methods that assess organic N availability. One incubation and three chemical methods were compared in twenty samples of unlimed or limed soils in a pot experiment with maize (Zea mays, L). The N availability methods included the NH4 +‐N released from soils by: a) anaerobic incubation for 7 days at 40°C; b) 2 mol/L KC1 at 100°C for 4 hours and distilled with MgO (hot KCl); c) this same procedure but distilled with 5 mol/L NaOH (hot KCl‐NaOH); and d) 30% v/v H2O2 and MnO2. In addition, inorganic N, total N and organic C were also determined in the soil samples. Readily available inorganic N presented the highest correlation coefficient with N uptake by maize but anaerobic incubation, hot KCl, hot KCl‐NaOH, and total N were also good predictors of soil N availability. The H2O2/MnO2 procedure and organic C produced inconsistent results. The amounts of N extracted by the meth...

Effect of water and citrate solubility on agronomic effectiveness of acidulated phosphates in three consecutive corn crops

No processo de acidulacao de fosfato de rocha, varios compostos classificados como impuros podem ser obtidos paralelamente aos fosfatos de calcio e de amonio. Tais compostos normalmente reduzem o teor de P soluvel em agua e a eficiencia agronomica dos fertilizantes. Com o objetivo de estudar este problema, desenvolveu-se um experimento em casa de vegetacao; tres cultivos sucessivos de milho foram feitos em amostras de um Latossolo Vermelho-Amarelo em esquema fatorial completo (6 x 2 x 2), com quatro repeticoes. Seis fertilizantes fosfatados acidulados comerciais foram adicionados a 2 kg de solo na dose de 70 mg kg-1 de P, a qual foi determinada de acordo com o teor de P soluvel em citrato neutro de amonio + agua (CNA + H2O) dos fertilizantes. Os fertilizantes foram aplicados na forma original ou lavados para remover a fracao de fosforo soluvel em agua e incorporados em volume total de terra ou com 1 % do volume. As plantas de milho foram colhidas apos 40 dias da emergencia e a materia seca e P acumulado foram determinados. No primeiro cultivo, e aplicacao localizada, a eliminacao do P soluvel em agua dos fertilizantes originais resultou em menor quantidade de P biodisponivel as plantas. Nos demais cultivos, os efeitos de fonte de fosforo, lavagem e metodo de aplicacao nao foram tao evidentes como no primeiro cultivo, sugerindo que as fontes de P testadas podem ter eficiencia semelhante quando se consideram varios cultivos. Concluiu-se que a fracao insoluvel em agua, porem soluvel em CNA, dos fertilizantes testados nao deve ser vista como totalmente inerte, uma vez que pode disponibilizar fosforo a longo prazo.

Evaluation of mixed cation–anion exchange resins as extractants for potentially available micronutrients in tropical soils

We examined the possibility of using mixed cation–anion exchange resinspre-treated with two organic acid ligands, acetate (R-ACET) and tartrate(R-TART) for extraction of phytoavailable Fe, Mn, Cu and Zn using theconventional diethylenetriaminepentaacetic acid (DTPA) as a referenceextractant. In each soil, variable amounts of Fe, Mn, Cu and Zn were extractedby the different extractants. The amounts of Fe, Mn, Cu and Zn did not followprediction based on stability constants of metal-organic complexes. The R-ACETwas a slightly better predictor of soybean uptake of Cu and Mn, and dry matter(DM) yield responses to Cu than either DTPA or R-TART, though differencesbetweenR-ACET and DTPA were not significant. However, soybean DM yield response to Znwas best predicted by DTPA, while Zn uptake correlated more strongly with DTPAthan R-ACET and R-TART extractable Zn. These results suggest that R-ACET may beused as an alternative extractant for Fe, Mn, Cu and Zn in strongly weatheredtropical soils, but it was not superior to DTPA.