Zinc influences nodulation, disease severity, leaf drop and herbage yield of alfalfa cultivars

Zinc deficiency is an important limiting factor in sustainable crop product ion and is a factor often overlooked in determining the benefits and overal l success of alfalfa pastures in rotations. A field experiment was conducte d to investigate the effects of zinc and alfalfa cultivars on nodulation, h erbage yield, leaf drop and disease severity (Phytophthora root rot disease and common leaf spot disease) in alfalfa ( Medicago sativa L.). Ten cultiv ars of alfalfa (Hunter River, Hunterfield, Sceptre Aurora, Genesis, Aquariu s, Venus (Y8622), PL69, P5929 and PL34HQ) were tested at two levels of zinc (+Zn: 4 kg ha(-1), -Zn: no zinc added) on a Zn-deficient soil (DTPA zinc o f top 0-15 cm soil was 0.4 mg kg(-1) soil, while 15-30 cm subsoil Zn was 0. 1 mg kg(-1) soil) under field conditions. Zinc application significantly in creased number and dry weight of nodules, herbage yield and leaf to stem ra tio of alfalfa plants. There was a significant reduction in leaf drop, and occurrence of Phytophthora root rot (caused by fungus Phytophthora megasper ma f. sp. medicaginis) and common leaf spot (caused by fungus Pseudopeziza medicaginis) diseases with Zn application. Alfalfa cultivars had a differen tial response to low Zn. Hunter River and Hunterfield were the most affecte d by omitting zinc application, while Sceptre, PL34HQ and Aquarius were com paratively less affected. The present study suggest that Zn nutrition effec ts nodulation, leaf drop, disease occurrence and production potential of al falfa. The alfalfa cultivars have differential ability to low Zn supply. Gr owing of Zn-efficient cultivars and adequate Zn nutrition may also improve the N-2-fixation by alfalfa on low-Zn soils.