Production and decay of structural root material of winter wheat and sugar beet in conventional and integrated cropping systems

Abstract

Production of structural root material of sugar beet and winter wheat was quantified by analysis of root growth and decay in a time series of minirhizotron images, combined with a single auger sampling. Cumulative root production of winter wheat was about 1700 kg ha−1 for conventional crp management and 1960 kg ha−1 for integrated (less pesticides and mineral fertilizer, less intensive soil tillage and more organic manure) crop management; in 1990 the difference between the two management systems was statistically significant. At harvest time 85% and 68% (in 1986 and 1990, respectively) of this structural root production remained as intact roots in the soil in both management systems. For sugar beet total fine root production was estimated at 1150 kg ha−1 in 1987 and 1989, with a significantly lower amount on the field on which minimum tillage was introduced in 1986; on average 47% of total root production remained as intact roots at harvest.Winter wheat root decay was studied with litter pots after crop harvest and in the following growing season. Initially, the N concentration in remaining roots increased while dry weight decreased. No net immobilisation or mineralisation of N and P during autumn was evident. During the next growing season net mineralisation was proportional to loss of root weight in an exponential decay with a half-life of 600 degree days (daily temperature sum). This N release pattern during the next growing period thus contributes to the synchrony between N demand and supply, but no difference between the two management systems was found.