Effect of zeolitite addition on soil properties and plant establishment during forest restoration

Zeolitites, rocks with a content of zeolite group minerals greater than 50%, can serve as support for plant nutrient uptake, by enabling the slow release of macro- and micronutrients over time. Zeolitites equally improve soil cation exchange and water holding capacity. We analyzed the effect of zeolitite addition to the soil in forest restoration. We hypothesized that zeolitite ameliorated soil quality and consequently improved sward restoration and seedling establishment. Soil treatments were applied in 2014 and consist of: ploughed and ripped soil (non-amended) and ploughed, ripped and amended with zeolitite soil (amended). After application of the soil treatments, a herbaceous mixture was hand sown. Oak (Quercus robur L.), hawthorn (Crataegus monogyna Jacq.) and elm (Ulmus minor Mill.) seedlings were planted twice in the area, in autumn 2014 and autumn 2015. We monitored soil, sward and seedlings from 2015 to 2017. Seedling survival, which was generally above 50%, was never affected by zeolitite addition. The effect on seedling growth was significant only for hawthorn planted in 2015 that was approximately 5 cm taller in the amended soil. Herbaceous vegetation was also slightly affected by zeolitite addition. The zeolitite increased nitrogen (N) and phosphorus (P) Olsen in 2015, and exchangeable potassium (K) during the whole study period. Other parameters, such as year and growing season had significant effects on soil, sward and seedling dynamics. Time since restoration, plant-plant interactions, mechanical site preparation and meteorological conditions all together influenced the restoration dynamics more than zeolitite application.