Abstract
Fast-growing willows (Salix spp.) provide alternative sources of renewable energy generation, but need an adequate nutrient availability in the soil for high biomass production. In general, species mixtures can be more nutrient-efficient than pure cultures, but this is scarcely known for Salix spp. Therefore, this study evaluates the nutrient availability and P mobilization under two willow species, Salixdasyclados var. ‘Loden’ and S. schwerinii × viminalis var. ‘Tora’, grown as pure and mixed cultures at non-fertilized former arable sites in Germany (Stagnic Cambisol) and Sweden (Vertic Cambisol). The plant availability of potassium (K), magnesium (Mg) and phosphorus (P) and soil phosphatase activities in the topsoil were measured in spring of the year of planting (initial) and under 4 years-old stocks (one year after the first 3-year cutting cycle). The initial plant availability of the nutrients significantly differed between the sites and the two sampling dates at both sites. The plant availability of K and Mg was optimal to high at both sites and sampling dates, but rather low for P (after 4 years ≤5 mg P 100 g−1 soil). The plant-available P and K content in soil significantly decreased within the 4 years of willow growth at both sites. The acid and alkaline phosphatase activity in the soil of the German site (Rostock) was significantly lower after 4 years of willow growth, but differed not significantly between the two sampling dates at the Swedish site (Uppsala). Higher activity of acid phosphatase compared to alkaline phosphatase was recorded in the soils at both test sites based on the site-specific soil pH (<7). The slight decrease of plant availability of P after 4 years of Salix growth in pure culture differed not significantly between the different species. Mixed growth did not decrease the plant availability of P within this period, although no significant difference in the biomass production of pure and mixed growth was observed. This was valid at both sites, and therefore, seems independent of the site-specific differences in soil and climate conditions. The general validity of the assumptions should be tested also for other species mixtures and soil conditions in the future before site-adapted growth designs can be recommended in biomass production of Salix.
Highlights
Short rotation coppices (SRCs) with poplar (Populus) and willows (Salix) species can be established on many types of land, including marginal lands that are unsuitable for agriculture [1,2]
The species/variety pool of the trial in Uppsala includes four different Salix varieties partly belonging to different species [37], of which the pure and mixed culture for two of them was selected for the present study: Salix dasyclados var
The plant-available concentrations of P and K in soil significantly decreased with the progressing willow growth at the test site Rostock (Figure 1 and Table 1)
Summary
Short rotation coppices (SRCs) with poplar (Populus) and willows (Salix) species can be established on many types of land, including marginal lands that are unsuitable for agriculture [1,2]. SRC plantations have ecological benefits compared to annual crops. They improve the soil water retention, enhance biodiversity in comparison to agricultural monocultures, improve water quality, protect ground water, prevent soil erosion and it is a low-input agricultural practice, implying low greenhouse gas emissions due to limited applications of chemicals [6,7,8,9,10] SRCs have been investigated intensively for the last 20 years (reviewed by Rödl [11]). Poplar is typical for Western and Central European floodplains, where willow is more tolerant to low temperatures and can grow further north and in continental climates in the east of Europe [16]
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