Soil, biomass, and management of semi-natural vegetation - Part I. Interrelationships

The interrelationships between biomass characteristics and soil properties (including in situ annual nitrogen mineralization) were statistically investigated in a descriptive study using a broad range of plant communities in unfertilized road verges. Not only the dependence of biomass characteristics on soil properties, but also the possibility of inferring soil nutrient availability from biomass characteristics was investigated. Possible effects of vegetation management (mowing) and overstory trees (shading) were accounted for. Annual aboveground biomass production was mainly explained by annual N mineralization, average soil moisture content, shading intensity, and soil pH (optimum at pH-CaCl2 5.7). Average tissue nutrient concentrations were primarily explained by mowing frequency, shading intensity, the availability of the corresponding soil nutrient, and pH (optima between 5.5 and 6.0). Results also implied that making hay twice per year removes more nutrients than a single cut at the end of the season. N mineralization may be inferred from the aboveground biomass production, but only across sites with equal moisture and shading conditions (partial r=0.74). In general, it is concluded that nutrient availability can only be deduced from biomass characteristics if sites with similar moisture content are compared. The only exception to this general rule is K availability. The latter was mainly indicated by the K concentration in vegetation biomass (partial r=0.80), and the confounding effect of other factors was small (bivariate r was still 0.71). Soil available P could not be satisfactorily indicated, even across sites with equal moisture and shading conditions. Also, different nutrients appeared to interact, and should not be considered in isolation. K was the only element with a strong relationship between its soil and tissue concentration. For the other nutrients, tissue concentrations did not depend predominantly on the soil availability. It seems most likely that the species occurring in semi-natural vegetation are adapted to the local fertility by means of their physiology or growth rate. It is concluded that, with the possible exception of K, simple relationships between soil properties and biomass characteristics cannot be expected over wide environmental gradients.