Effects of Soil Amendments and Tillage on Vesicular-Arbuscular Mycorrhizal Fungus Colonization of Citrus

in HortTechnology
Author: S. Nemec 1
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  • 1 U.S. Department of Agriculture, Agricultural Research Service, 2199 South Rock Road, Fort Pierce, FL 34945-3138.

Three sites (A-C) were prepared for citrus groves in Florida from 1985 to 1986. Nine soil amendments applied at either one or two rates were deep-tilled 3.9 to 4.9 ft (1.2 to 1.5 m) deep and 4.9 ft (1.5 m) wide in the row before planting. Maximum treatment rates were limestone 50,000 at lb/acre (56 000 kg·ha−1), phosphoclay at 80,000 lb/acre (89 600 kg·ha−1), humate at 77,612 lb/acre (86 912 kg·ha−1), shrimp waste at 73,052 lb/acre (81 805 kg·ha−1), peat at 250,000 lb/acre (280 000 kg·ha−1), bentonite clay at 73,051 lb/acre (81 805 kg·ha−1), mined gypsum at 2000 lb/acre (2240 kg·ha−1), calcium humate at 2000 lb/acre (2240 kg·ha−1), and phosphogypsum at 10,000 lb/acre (11 200 kg·ha−1). Deep-tilled controls and a no-till control were established at sites A and B and a deep-tilled control at site C. A fourth grove (site D) was planted in 1970 and included the treatments surface tillage (ST), deep tillage (DT), and DT plus lime (DTL) at 45,407 lb/acre (50,848 kg·ha−1). Mycorrhizal fungus infection was found in roots in 1987 at sites A and B and in 1989 in site C. Fungus infection ranged from 6% (no-till control) to 64% at site A, 64% to 81% at site B, and 15% to 47% at site C. At all sites, amendments did not increase percentage infection and vesicle and hyphae ratings significantly over the deep-tilled control. At site A, percentage infection in the limestone treatment was the highest (64%) and was significantly higher than infection in phosphogypsum, peat, and the no-till control treatments. No treatment had a suppressive effect on infection. Mycorrhizal infection in roots was high (94% to 95%) at site D but did not differ significantly between treatments.

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