Risk potential of secondary soil salinization by repeated application of chicken and pigeon manure

Six consecutive field trials of Brassica parachinensis were conducted to evaluate risk potential of secondary soil salinization by successive application of chicken and pigeon manure from intensive poultry farms. It is noted that soil total soluble salt (TSS) concentration rises from low to medium levels by fertilization after the third crop during the dry season.K⁺, Na⁺, Ca²⁺, Mg²⁺, SO₄^2- and Cl^- markedly accumulate in the soil with increased salt concentrations, while, K⁺, Na⁺,SO₄^2- and Cl^- concentrations are elevated as chicken and pigeon manure application rates increase. Meanwhile, soil pH decreases by 0.04～0.19. After the sixth crop, there is an obvious reduction in soil TSS and Ca²⁺ concentration compared to their original levels before the trials, a phenomenon ascribed to leaching from heavy precipitation during the latter three crops. Nevertheless, K⁺，Na⁺，Mg²⁺，SO₄^2- and Cl^- continue to accumulate in the soil from chicken and pigeon manure application. Soil pH increases in the range of 0.04～0.31. Hence, secondary soil salinization probably occurs by successive poultry manure application,which is true even in south China. Heavy application at a time or repeated application of poultry manure from intensive poultry farms should be avoided in vegetable production to prevent secondary soil salinization.