Effects of organic soil amendments and irrigation frequency on shrub growth during establishment

Abstract

Irrigation management is an important component of the urban landscape. Poor growth of container-grown plants during landscape establishment and/or transplant failure is generally attributed to water stress. The addition of organic matter (OM) to soil is known to improve the soil’s ability to store and transmit air and water. Our objective was to evaluate the addition of composted cow manure (Black Kow) or yard waste in relation to irrigation frequency (water every 2 or 4 d) on the growth of Hibiscus rosa-sinensis L. (hibiscus) and Viburnum odoratissimum Ker-Gawl. (sweet viburnum) in a landscape setting during the first year after planting. Canopy growth index (GI) measured 28 and 52 weeks after planting (WAP) was greater for hibiscus and sweet viburnum plants watered every 2 d than for plants watered every 4 d. There were no differences in GI or root extension at 28 or 52 WAP due to the addition of OM to the soil. The addition of composted cow manure or yard waste did not appear to influence soil organic matter content or soil moisture. Soil moisture measurements, however, were lower for plants watered every 2 d than for plants watered every 4 d. The addition of composted cow manure did significantly increase the concentration of Mehlich 1 phosphorus (P), potassium (K), and magnesium (Mg) in the soil compared to the addition of yard waste or in unamended soil. Results of our study suggest that increased irrigation frequency enhanced hibiscus and sweet viburnum shoot growth, while the addition of OM (as composted cow manure or yard waste) had no effect on plant growth.