Micronutrient Supply from Pine Bark and Micronutrient Fertilizers

Abstract

The average water-extractable micronutrient content of pine bark, with the exception of Fe, is similar to Hoagland’s micronutrient solution (Ogden et al., 1987). Yet, amending bark with micronutrients is a common nursery practice. Both positive plant growth responses (Penningsfield, 1972; Whitcomb, 1978, 1984) and no growth responses (Conover et al., 1975; Leda, 1986) have resulted from the addition of micronutrients to container media. In one case, response to micronutrient addition was found to depend on addition of lime (Wright and Hinesley, 1991). The method used for extracting micronutrients is important in assessing micronutrient availability. Berghage et al. (1987) and Handreck (1989) found the extractant diethylenetriaminepentaacetic acid (DTPA) to be a relatively reliable indicator of media micronutrient status. The quality of DTPAextracted micronutrients was highly correlated with growth (Handreck, 1989). Container-grown nursery crops are irrigated with as much as 4500 mm of water per growing season, but the effect of this leaching on micronutrient supply has not been documented using DTPA as the extractant. Broschat and Donselman (1985), evaluating several micronutrient fertilizers, showed relatively constant micronutrient supplies over time in irrigated media; however, ammonium acetate, which has been shown to be a relatively poor indicator of media micronutrient status (Handreck, 1989), was used as the extractant. Handreck (1989) determined the DTPA iron content of Pinus radiata D. Don bark, but no reports have documented the DTPA extractable Cu, Fe, Mn, and Zn of pine (P. taeda L.) bark, Additionally, there have been no reports documenting DTPA extractable micronutrients from bark amended with micronutrient fertilizers. I, therefore, determined the DTPA-extractable micronutrient supply of pine bark amended with two micronutrient fertilizers (Micromax and Ironite) as influenced by irrigation rate. Pine bark, amended with 3 kg dolomitic