Soil Type and Phosphorus Fertilization Affect Poa annua Growth and Seedhead Production

Abstract

Core Ideas Excessive P fertilization produced larger Poa annua plants. Excess P fertilization created Poa annua plants that flowered earlier. Limiting P fertilization will help to create smaller Poa annua plants. Annual bluegrass (Poa annua L.) is a winter annual weed in southern landscapes. Previous research indicated that soil P or pH affects growth of annual bluegrass, which could provide tools for integrated control of a plant considered a weed in some turfgrass systems. The objective of this work was to evaluate the effects of P rate and soil type on growth parameters of annual bluegrass. This greenhouse study evaluated rates of P (0, 25, 50, 99, and 197 kg P ha−1) on 3 soil types (silty clay loam, loamy sand, and sand/peat [90:10% v/v] greensmix). Plant height, days to first seedhead (panicle), branches per panicle, seeds per branch, seed number and weight, and shoot and root dry weight data were collected by hand sampling and counting. Annual bluegrass seed was affected by both soil type and rate of P fertilization. Annual bluegrass plants grown in greensmix that received lower or zero P were 25% smaller than fertilized, took a week longer to produce a visible seed head, and had seed of reduced weight. Number of panicles, branches per panicle, seeds per panicle, and seeds per panicle branch were all unaffected by P rate, but often by soil type, where there were fewer of all when grown in greensmix. Avoidance of excessive P fertilization and subsequent accumulation of soil P may be an additional tool for the management and reduction of annual bluegrass.