INFLUENCE OF SUBSOIL ZINC ON DRY-MATTER PRODUCTION, SEED YIELD AND DISTRIBUTION OF ZINC IN OILSEED RAPE GENOTYPES DIFFERING IN ZINC EFFICIENCY

The effects of Zn supply (+Zn: 1 mg kg(-1) soil, -Zn: no Zn added) in subsoil were examined in three genotypes of Brassica napus (Zhongyou 8 21, Xinza 2, Narendra) and one genotype of Brassica juncea (CSIRO-1) i n a glasshouse experiment in pots (100 cm long, 10.5 cm diameter). The topsoil (upper 20 cm soil in pots) was supplied with Zn in all treatm ents whereas Zn was either supplied or omitted from the subsoil. Suppl ying Zn to subsoil significantly increased the root growth in the lowe r zone, markedly decreased the number of aborted and unfilled pods pla nt(-1) and significantly increased the number of developed pods plant( -1), number of seeds pod(-1), individual seed weight and overall seed yield. Subsoil Zn also significantly increased the Zn concentration an d Zn content of seed and improved the ratio of Zn uptake by seed to to tal Zn uptake by seed and shoots. These effects of subsoil Zn were mor e pronounced in Zhongyou 821, Xinza 2 and Narendra compared with CSIRO -1. CSIRO-1 had 92% Zn efficiency (ratio of-Zn subsoil seed yield to Zn subsoil seed yield expressed in percentage) compared with 63% for Z hongyou 821. Among the four genotypes, CSIRO-1 had the lowest Zn conce ntration in roots and shoots but highest Zn concentration and content in seed, suggesting it has a superior Zn transport mechanism from sour ce (roots) to sink (seed). CSIRO-1 also significantly decreased the rh izosphere pH in lower rooting zone (20-93 cm) in -Zn subsoil treatment compared with +Zn treatment.