Continuous agricultural production in the Amazon region requires correction of soil acidity and understanding of the long-term interactions of liming with chemical soil properties. The objective of this study was to evaluate the immediate and residual effects of lime on annual crop production and soil properties of medium-textured Oxisols in the Brazilian Amazon. Field experiments were conducted at two locations in the Northeast of Pará from 2003 to 2008, one in the county of Terra Alta and the other in Tracuateua. An unlimed control and limed treatments were distributed in a randomized complete block design for both experiments. Ten lime rates between 0.1 and 2 Mg ha-1 were assessed in Terra Alta and four lime rates between 1 and 4 Mg ha-1 in Tracuateua. Two varieties of each corn and cowpea in an annual rotation were evaluated in the subplots. Four corn crops (2003-2006) in rotation with three cowpea crops (2004-2006) were evaluated in Terra Alta. Maximum corn grain yields were achieved in Terra Alta with applications of 1 Mg ha-1of lime whereas maximum cowpea yields required lower lime rates. In Tracuateua, cowpea yield response to lime applied in 2003 was first observed in the 2005 harvest, with a maximum yield obtained with the residual lime rate of 1 Mg ha-1, with significant differences between varieties. Yield responses of both crops to lime were associated with increased soil Ca + Mg levels and reduced Al saturation. Trends in declining soil Ca + Mg and increasing Al saturation with time after liming were observed at both sites, but were more pronounced in Tracuateua. Corn planted in 2007 and 2008 in Tracuateua provided linear yield responses to rates of up to 4 Mg ha-1 of lime. Collective data from both sites indicated that the appropriate lime rate for corn in these soils should reduce Al saturation to less than 11 %. The importance of varietal selection with cowpea was illustrated by the difference in Al saturation tolerance, which ranged between 13 and 32 % among the varieties evaluated.
Amazon region; acid soils; lime; corn; cowpea
