Effect of Soil Amendments on Cd Accumulation by Spinach from a Cd-Mineralized Soil

Cadmium (Cd)-mineralized soils occur in many nations. When these soils are noncalcareous, crops and especially leafy vegetables such as lettuce ( L.) and spinach ( L.) may accumulate levels of Cd in their edible portions that exceed international standards. Vegetable crops grown on Lockwood loam from Monterey County, CA, absorb an excessive amount of Cd into their edible portions. Agronomic or genetic management alternatives are needed to allow the use of these otherwise highly productive soils for spinach. Previous research has shown that zinc (Zn) fertilizer plus limestone incorporation or biosolids compost and sorbent oxide amendments can reduce spinach and lettuce Cd accumulation. We tested combinations of biosolids compost (10%), Mn, Zn, and limestone (5%) on Cd phytoavailability. Manganese sulfate (in the absence of limestone) caused minor pH reduction, which increased the Cd level in spinach. The addition of ZnCO+ZnSO inhibited Cd accumulation, as did biosolids compost, but much greater reductions were achieved when soil pH was raised with limestone to prevent the acidification from the addition of compost or Zn salts. Cadmium accumulation was suppressed below international guidelines limits when combinations of compost+Zn+limestone or compost+Zn+Mn+limestone were applied, highlighting the complexity of processes limiting Cd phytoavailability.