Cyclic Sprinkler Irrigation of Container Substrate Affects Water Distribution and Marigold Growth

Abstract

Abstract Two experiments were conducted to determine how cyclic sprinkler irrigation (daily water allotment applied in more than one application) influenced water distribution and leaching, and marigold growth in a pine bark (PB) or a PB:sand (S) substrate. Marigolds (Tagetes erecta L. ‘Apollo’), were grown in PB-filled 3.8 liter (1 gal) containers. Substrate was allowed to dry via evapotranspiration (ET) to targeted pre-irrigation substrate water contents (PSWC) and respective ET volumes were applied as a single application (continuous) or by multiple applications (cyclic irrigation) via a simulated sprinkler irrigation system; leachates were collected. In the first experiment, the influences of irrigation method, continuous and cyclic irrigation, on water distribution in the top, middle and bottom substrate (9: 1pine bark to sand, by vol) sections were investigated. Two hundred seventy five (275) ml were applied continuously or cyclically (three 92 ml allotments with 1 hr interval between applications) to containers at 84 % of container capacity (CC). In the second experiment, marigolds were grown in a growth chamber for three weeks and received 12 irrigations. In each irrigation, a complete nutrient solution was applied continuously or cyclically (three applications each of one-third of the total volume with 1 hr between applications). Substrate solution N concentration (via pour-through method), leachate N, and plant growth was measured. In the first experiment, gravimetric water contents of top and middle substrate sections were similar, whereas the water content of the bottom section was higher with cyclic than with continuous. In the second experiment, root dry weight was 43% higher, shoot fresh and dry weights were similar, and plant N concentration was 0.7% higher (absolute basis) with cyclic than with continuous irrigation. Irrigation method had no influence on substrate solution and leachate NO3-N and NH4-N concentrations. However, total N leached was 43% higher with continuous than with cyclic irrigation. These results demonstrate that cyclic irrigation increased root N concentration and root growth without a toxic accumulation of N in the substrate solution.