Liming Effects on the Yield and Composition of Perennial Ryegrass Treated with Sewage Sludge Contaminated with Heavy Metals

Abstract

Up to 12% of the dry matter of a sewage containing 0.65% Zn, 0.20% of Ni, 0.5% Cu, and 0.41% Cr was mixed with an acid loamy sand limed to give a pH range from 4.6 to 7.0 and cropped with ryegrass in pots. The results obtained were similar to a previous experiment (2). Yields of three cuts of grass were reduced by the largest amounts of sludge at soil pH’s less than 6. However, grass yields were increased by medium amounts (8%) of sludge at soil pH more than 6. The increases in yield were caused by increased supplies of N, P, Mg, and S from the sludge. Concentrations of more than 300 ug/g Zn, and 200 ug/g Ni in the grass dry matter were associated with lowest yields. The treatments had only small effects on Cu concentrations. Acetic acid-extractable metals in the cropped air-dried soils were increased by the maximum sludge addition to 300 mg/Kg Zn, 100 mg/Kg Cu, 67 mg/Kg Ni, equivalent to 30% of the total applied Zn, 17% of Cu, and 28% of Ni. The pH of the sludge (5.0) significantly affected soil pH. Sludge used on agricultural land should be adjust to pH 7.0 before spreading so as to minimize any possible heavy metal toxicities to crops. 為繚解施用石灰對於污染重金屬腐泥肥效之改進，特在人工氣象室內舉行盆栽試驗，所用土壤為酸性壤砂土，腐泥用量分為4平準，最高達土壤用量的12%，石灰用量亦為4平準，土壤pH從4.6調整至7.0，並以裸麥草（Rye grass）為指示作物，三次收割後，裸麥草乾物及栽培後土壤經用X-ray fluorescence spectrometer原子吸光儀及Technicon自動分析儀測定結果，摘要於後。 1. 施用大量腐泥，使土壤pH降至6.0以下時，顯然因重金屬為害，降低裸麥草收量；若施用中量腐泥，保持土壤pH在6.0以上，則可提高裸麥草收量，此乃由於重金屬為害減弱，腐泥供應主要營養素如氮、磷、鎂及硫等所致。 2. 裸麥草乾物中鋅濃度超過300ppm，鎳濃度超過200ppm時，將降低裸麥草收量。 3. 栽培後土壤中醋酸可抽出鋅、銅、及鎳濃度隨腐泥用量而提高，鋅高達300ppm，銅100ppm，鎳67ppm，均超出英國農部規定標準。 4．釀性腐泥可影響土壤pH，施用農田之前，必須先調整pH為7.0，藉可減少重金屬為害的可能性。