Spatial and temporal distribution of the root system and root nutrient content of an established Miscanthus crop

Although a high biomass yield is obtained from established Miscanthus crops, previous studies have shown that fertilizer requirements are relatively low. As little information on the role of the Miscanthus roots in nutrient acquisition is available, a study was conducted to gather data on the Miscanthus root system and root nutrient content. Therefore in 1992, the root distribution pattern of an established Miscanthus crop was measured in field trials using the trench profile and the auger methods. Also, in 1994/1995, seasonal changes in root length density (RLD) and root nutrient content were monitored three times during the vegetation period. The trench profile method showed that roots were present to the maximum depth measured of 250 cm. The top soil (0-30 cm contained 28% of root biomass, while nearly half of the total roots were present in soil layers deeper than 90 cm. Using the auger method, we found that RLD values in the topsoil decreased with increasing distance from the centre of the plants. Below 30 cm, RLD decreased markedly, and differences in root length in the soil between plants were less pronounced. The total root dry weight down to 180 cm tended to increase from May 1994 (10.6 t ha(-1)) to November 1994 (13.9 t ha(-1)) and then decreased again until March 1995 (11.5 t ha(-1)). Nutrient concentrations in the roots decreased with increasing depth. The concentrations of N (0.7-1.4%) and K (0.6-1.2%) were clearly higher than those of P (0.06-0.17%). The mean values for N, P and K contents of the roots of all three sampling dates in 1994/1995 were 109.2 kg N ha(-1), 10.6 kg P ha(-1) and 92.5 kg K ha(-1). Although our results showed that RLD values for Miscanthus in the topsoil are lower than for annual crops, the greater rooting depth and the higher RLD of Miscanthus in the subsoil mean that nutrient uptake from the subsoil is potentially greater. This enables Miscanthus crops to overcome periods of low nutrient (and water) availability especially during periods of rapid above-ground biomass growth.