Phosphorus in Albaqualf soil cultivated with dryland crops and its availability for the subsequent rice under no tillage

O objetivo geral deste estudo foi avaliar o efeito da aduba????o fosfatada e a disponibilidade das formas de f??sforo para o arroz irrigado cultivado em Planossolo no sistema plantio direto, ap??s o cultivo de culturas de sequeiro. Os experimentos foram conduzidos desde 2003, delineados em blocos ao acaso com quatro repeti????es e os tratamentos foram dispostos em um fatorial 2 x 2 (superfosfato triplo - SFT) e fosfato natural de Arad - FNA), com e sem reaplica????o anual de P com SFT) mais um tratamento adicional testemunha sem a aplica????o da aduba????o fosfatada. Foram coletadas amostras de solo em duas profundidades (0 - 10 cm e 0 - 20 cm), analisadas pelo m??todo Mehlich-1 e resina de troca ani??nica (RTA), e amostras de 0,0 - 2,5; 2,5 - 5,0 e 5,0 - 15,0 cm, analisadas pelo fracionamento de P. Nas plantas fez-se determina????o da concentra????o de f??sforo nas folhas bandeira e parte a??rea (folhas, colmo e gr??os) e quantidade total acumulada de P nas plantas, calculada a partir da concentra????o de f??sforo na parte a??rea em rela????o ?? massa de mat??ria seca. Foi realizada a colheita dos gr??os ap??s a matura????o fisiol??gica para an??lise de rendimento. O rendimento de gr??os de arroz n??o respondeu ?? aduba????o fosfatada, mesmo com teores inicias de P no solo abaixo do n??vel cr??tico (< 6,0 mg dm-3). A aduba????o fosfatada realizada nas culturas de sequeiro (milho e soja) apresentou um efeito residual para o arroz irrigado mesmo ap??s quatro anos de cultivos destas, no sistema plantio direto. Os extratores Mehlich-1 e resina de troca ani??nica foram igualmente eficientes na avalia????o da disponibilidade de P para o arroz irrigado. Os teores de P extra??dos do solo pelos dois m??todos apresentaram correla????es significativas com o P acumulado nas plantas. O fosfato natural de Arad apresenta desempenho semelhante ao superfosfato triplo no que se refere ?? nutri????o por f??sforo em arroz irrigado em rota????o com culturas de sequeiro no sistema plantio direto. As fra????es de f??sforo inorg??nico que predominam em um Planossolo cultivado com as culturas de milho e soja em sistema plantio direto s??o as extra??das com NaOH 0,1 e NaOH 0,5 mol L-1. As aduba????es realizadas anualmente com superfosfato triplo e fosfato natural de Arad aumentaram todas as fra????es inorg??nicas de f??sforo no solo, desde as mais l??beis at?? as menos l??beis. As fra????es org??nicas apresentam-se pouco sens??veis ?? aduba????o fosfatada. As quantidades de f??sforo acumuladas na parte a??rea das plantas de arroz melhor se correlacionaram com as fra????es de f??sforo mais l??beis (RTA, NaHCO3 e NaOH 0,1 mol L-1), principalmente na profundidade de 0,0 - 2,5 cm.The general objective of this study was to evaluate the effect of the phosphorus fertilization and the availability of the phosphorus forms in irrigated rice under no tillage in Albaqualf soil cultivated on dryland crops mulch. The experiments installed in 2003 were conducted under a randomized blocks design with four replications. The treatments were disposed in 2 x 2 factorial (triple superphosphate - TSP) and Arad rock phosphate (ARP), with and without annual replication of P with TSF). Additionally, it was conducted a treatment under natural condition (without the application of the phosphorus fertilization). The soils collected from the layers: 0 - 10 cm and 0 - 20 cm were analyzed using the Mehlich-1 and anion-exchange resin methods. Soils collected from 0.0 - 2.5; 2.5 - 5.0 and 5.0 - 15.0 cm was used to evaluate the P fractions. Analysis of P concentration in flag leaves and shoot (leaves stalk and grain) were also evaluated. Total P accumulated was calculated from the shoot P concentration in relation to the dry matter. For the future analysis, the rice harvest was done when the plants were in physiological maturity stage. The phosphorus fertilization did not affect the production of rice grains; even though with initial P soil level below of the critical level (< 6.0 mg dm-3). The phosphorus fertilization applied to the dryland crops (maize and soybean) presented a residual effect to subsequent irrigated rice, even after four years of experiment under notillage management. For the irrigated rice no differences were shown between the results of P availability using the Mehlich-1 and anion-exchange resin methods. The P concentrations from the soils, using these two methods, presented significant correlations with the P accumulated in plants. The ARP presented similar performance as TSP regarding to the P nutrition in irrigated rice in rotation with dryland crops under no tillage. The P inorganic fractions that predominate in Albaqualf soil cultivated with maize and soybean under no tillage are extracted with 0.1 NaOH and 0.5 NaOH mol L-1. The fertilizations carried out annually with TSP and ARP had increased all the P inorganic fractions in soil. The organic fractions were not much affected by the phosphate fertilization. The P accumulated in shoot of rice plants was better correlated with the labile P fractions (anion-exchange resin, NaHCO3 and 0.1 NaOH mol L-1), mainly in the superficial layer (0.0 - 2.5 cm)