Phosphate fertilization to castor bean cultivars in Rio Grande do Sul State, Brazil/Adubacao fosfatada para cultivares de mamoneira no Rio Grande do Sul

The study was carried out from April 2007 to May 2008, on a Planossolo Haplico (Albaqualf, in Pelotas, RS, Brazil. The treatments comprised the castor bean cultivars 'AL Guarany 2002' and '.Lyra', with five rates of phosphate (0; 30; 60; 90 and 120kg [h.sup.-1] of [P.sub.2] [O.sub.5].These were arranged as a randomized complete block in a factorial design with three replications. Castor bean nutritional status and yield performance were evaluated. The phosphate fertilization altered castor bean foliar concentrations of nitrogen, calcium, boron, and iron. For boron, this effect was limited to the '.Lyra' cultivar The 'AL Guarany 2002' cultivar demanded more phophorus than 'Lyra' cultivar. Phosphate fertilization increased grain yield of both castor bean cultivars. Yield increased with the use of up to 156kg [ha.sup.-1] of [P.sub.2] [O.sub.5], for 'AL Guarany 2002' cultivar, and of up to 90kg [ha.sup.-1] of [P.sub.2] [O.sub.5], for 'Lyra' cultivar. The rates of maximum economic efficiency for 'AL Guarany 2002' and 'Lyra' cultivars were, respectively, -34kg [ha.sup.-1] and 78kg [ha.sup.-1] of [P.sub.2] [O.sub.5] Key words: Ricinus communis, phosphorus, fertilizer, nutritional status, castor bean grain yield. O estudo foi realizado na safra agricola 2007/08, em um Planossolo Haplico, em Pelotas, Rio Grande do Sul (RS). Os tratamentos compreenderam as cultivares de mamoneira 'AL Guarany 2002' e 'Lyra', com cinco doses de P (0; 30; 60; 90 e 120kg [ha.sup.-1] de [P.sub.2] [O.sub.5]), sendo dispostas em delineamento blocos ao acaso, em esquema fatorial, com tres repeticoes. Avaliaram-se o estado nutricional e o desempenho produtivo da cultura. A adubacao fosfatada alterou os teores foliares de N, Ca, B e Fe da mamoneira; para boro, o efeito restringiu-se a 'Lyra'. A cultivar 'AL Guarany 2002' mostrouse mais exigente em fosforo que a 'Lyra'. A adubacao fosfatada elevou a produtividade de graos de ambas as cultivares de mamoneira. Esta aumentou com o uso de ate 156kg [ha.sup.-1] de [P.sub.2] [O.sub.5], para a 'AL Guarany 2002', e de ate 90kg [ha.sup.-1] de [P.sub.2] [O.sub.5] para a 'Lyra', e as doses de maxima eficiencia economica para essas cultivares foram, respectivamente, de 134kg [ha.sup.-1] e 78kg [ha.sup.-1] de [P.sub.2] [O.sub.5]. Palavras-chave: Ricinus communis, fosforo, adubo, estado nutricional, produtividade da mamona.