Comparison of ingrowth core and sequential soil core methods for estimating belowground net primary production in grass–clover swards

Abstract

AbstractEstimation of belowground net primary production (BNPP) is crucial for prediction of grassland soil organic carbon sequestration, but there are high coefficients of variation (CV) among methods of estimation. We compared accuracy and precision of two variations of the traditional soil core method and three of the ingrowth core method, over 2 years on grass–white clover swards in Germany. The ingrowth core method (5‐ to 9‐week ingrowth period) provided the most accurate BNPP estimate (471 g m−2) with the highest precision (CV: 31%), whereas the two soil core approaches resulted in underestimation and high error. Comparing results with other grassland studies, we found that reliability of the ingrowth core method was influenced by ingrowth period and sward rooting pattern related to grass phenological stages, while the precision was determined by ingrowth period and grassland productivity. We therefore recommend using the ingrowth core method for managed grasslands where belowground productivity is relatively high and installation disturbance is likely to be negligible. Using a 6‐ to 8‐week ingrowth period, the method delivers reliable and feasible BNPP estimates for temperate managed grasslands which can be applied to long‐term soil carbon budget simulation. Results from our work and other studies also indicated that standing root biomass masks seasonal pattern of rooting due to synchrony between root birth and death. The soil core method is likely to lead to underestimates and higher errors than the ingrowth core methods and thus should be avoided.