Study on optimization of moisture retention for golf green rootzone soil mixtures

Most golf course green have been constructed with pure sand or sand-based rootzone mixes. As we know, high sand content provides rapid drainage despite sand’s inefficiency in retaining moisture. However, drainage capability and water retention are both essential elements to the golf course green, and the addition of peat could increase the soil moisture retention, therefore, the research on the drainage capability and water retention of the sandy golf green has become more and more important these years. In this study, extreme vertex design was applied which is one of the mixture experiment designs widely used in mixture experiments, the study investigated the effects of the thirteen different rootzone soil mixtures using middle-coarse, fine sand, very fine sand plus silt and clay as well as peat as the materials under three kinds of golf green profile (1-layer profile, 2-layer profile, 3-layer profile) conditions on the water retention of green rootzone. Through the qualitative, quantitative and optimization analysis of water retention capability of the sandy golf green, evidence a basis for choice of green profiles and rootzone matrix could be provided. And the significantly correlative regression model was established between the moisture retention and components of rootzone soil mixture. In addition, the order of factor contribution ratio, effect of single and double factor and optimization of the model were analyzed in detail. The results were as follows: both green profile and soil mixture, which had interaction of each other, had significant effects on soil moisture retention. Additional attributes include high porosity and greater water holding capacity than sand, and the higher content of peat, fine sand plus silt and clay, the better water retention. The mixtures had much higher water content in 1-layer profile than that in the other two profiles. There was significantly higher water content in 2-layer profile for pure sand mixtures (A–E) and low peat mixture (F) than that in 3-layer profile, while there was no higher water content for other 7 high peat mixtures (G–M) (>5%) in 2-layer than that in 3-layer profiles. The significance of key factors in rootzone soil mixture on moisture retention were: very fine sand plus silt and clay>peat>middle-coarse>fine sand. According to the moisture retention 15–25% specification of USGA (United States Golf Association), the optimal soil mixture in 1-layer profile was: middle-coarse 71.4–73.5%; fine sand 17.8–21.5%; very fine sand plus silt and clay 6.8–8.4%; peat 0–1%. The optimal soil mixture in 2-layer profile was: middle-coarse 65.0–73.4%; fine sand 17.8–20.5%; very fine sand plus silt and clay 7.5–8.9%; peat 0.2–6.3%. The optimal soil mixture in 3-layer profile was: middle-coarse 62.3–73.9%; fine sand 17.7–21.4%; very fine sand plus silt and clay 7.3–10.7%; peat 0–6.3%. These optimal recipes took through the limitation of previous research, which were practically important to golf green soil selection and profile design. Thus, both proportion and interaction should be considered when we choose the soil mixture.