Aluminum, Citric Acid, Nitrilotriacetic Acid, and Soil Moisture Effects on Aluminum and Iron Concentrations in Ryegrass1

Abstract

AbstractSeasonal variations in Al and Fe content of pasture forage samples have been generally attributed to soil contamination although mechanisms for plant Al uptake have been suggested. Aluminum and Fe concentrations in annual ryegrass (Lolium multiflorumLam.) grown at two soil moisture levels, flooded and 80% field capacity (FC), with Al added as chelates of citric or nitrilotriacetic acid (NTA) at 0, 33.5 67,100.5, and 134 mg kg−1or chelates added alone, were investigated in a greenhouse experiment. Effects of treatments on soil pH and exchangeable Al were investigated with and without plants present. Plants grown for 10 weeks were harvested at two heights: 6 cm [above 6 cm = upper growth] and ground level (0–6 cm = lower growth). Flooding, chelates, and A1‐chelates increased Al concentrations in plants harvested at both heights. In lower growth, Fe increased only in response to flooding and A1‐NTA. Highest tissue Al concentration occurred with addition of 134 mg Al kg−1as A1‐NTA with values of 850 and 140 mg kg−1in lower and upper growth, flooded, and 480 and 110 mg kg−1in lower and upper growth at 80% FC, respectively. Respective controls contained 410, 67, 133, and 37 mg kg−1Al. Flooding increased soil pH and exchangeable Al. Chelates and Al‐chelates increased soil exchangeable Al. Results show potential for increased plant Al concentrations, particularly under flooded conditions, and suggest chelation with organic acids as an Al uptake mechanism which could affect animal nutrition. For critical determinations, AI should not be used as an indicator of soil contamination in plant samples