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

Abstract

Estimation 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 grasswhite clover swards in Germany. The ingrowth core method (5-to 9-week ingrowth period) provided the most accurate BNPP estimate (471 g m À2 ) 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.

Nitrous Oxide Emission from Grazing Is Low across a Gradient of Plant Functional Diversity and Soil Conditions

“…It appears grass-legume swards are associated with the high N uptake, as corroborated in this study and by Reinsch et al [45]. This has been attributed to species complementarity evident by the development of high root length and root density by grass-legume species [69], leading to low PRN.…”

Core-labelling technique (CLT): a novel combination of the ingrowth-core method and tracer technique for deep root study

“…As hypothesized (i), CLT, with its deep access-tubes and ingrowth-core installation, was capable of capturing deep root growth below 2 m depth. To our knowledge, this study illustrates the deepest application of an ingrowthcore technique, which, has commonly been used to a maximum of 0.5 m soil depth [5,50]. We found alfalfa root growth and activity at 4.2 m depth in autumn, which exceeds the deepest observation on alfalfa roots, so far, done by Weaver [58] at 3.7 m after 6-years cultivation of the species.…”

Independence of seasonal patterns of root functional traits and rooting strategy of a grass‐clover sward from sward age and slurry application

“…The higher soil temperature in summer would additionally favour lateral root growth (Füllner et al ., ) and total root length accumulation (Edwards et al ., ; Pilon et al ., ) of grasses. Notably, this burst in lateral growth was not caused by installation of ingrowth cores (discussed in Chen et al ., ). Root systems with higher proportion of first lateral roots are more efficient for N acquisition when soil N is limiting (Dunbabin et al ., ).…”

“…This approach allowed roots to be sampled with minimum artificial disturbance (Chen et al ., ). Effects of the eight ingrowth periods and four treatments were tested for significance similarly by the three‐way anova and multiple comparisons.…”