Larger root biomass in organic than conventional farming systems
Root biomass is commonly estimated as a fixed fraction of shoot biomass. Now, a more reliable method of root biomass estimation, that differentiates crops grown in organic and conventional farming, is proposed.
Research in the GUDP project, RowCrop, shows that root biomass of cereals and catch crops can be reliably estimated without considering shoot biomass. Moreover, shoot and root biomass are influenced in different ways by cropping systems and crop management. Therefore, root biomass estimates based on knowledge about the agricultural practice are more reliable than estimates based on measurement of shoot biomass.
Data on cereal shoot biomass at maturity and root biomass (0-25 cm) at flowering were collected from cropping system experiments in Denmark. In addition, we collected shoot and root biomass of catch crops and weeds sampled in November. Shoot and root biomass was related to influential factors such as farming systems and fertilisation rates. Linear regression was used to test which variables affected shoot, root and the allometric ratios (e.g. root/shoot ratio).
For cereals, root biomass was affected by the type of farming system (organic versus conventional), species (wheat versus barley) and the variations of weather between years. For catch crops and weeds, the key factors were the type of farming system and the plant types (catch crops or weeds).
Methods of root biomass estimation were tested based on the key factors through a leave-one-out cross validation. Results showed that root biomass could be most reliably estimated when considering farming system, species and year. Estimates became less precise, but changed little, when ignoring yearly variations. Root biomass in Denmark and northern Europe can therefore be estimated from the following table, resulting in higher root biomass in organic farming than conventional farming systems. A reason for relatively greater amount of roots in the organic systems could be the lower availability of nitrogen in organic systems.
The results show consistently greater root biomass of cereal crops in organic compared to conventional systems, and there was greater root biomass in wheat compared to barley. The results also showed greater root biomass in catch crops compared with weeds. This suggests that soil organic matter inputs in arable organic systems are favoured by higher root inputs, and there is need to further study the effects of such differences on soil carbon and nutrient cycling.
Hu, T., Sørensen, P., Wahlström, E.M., Chirinda, N., Sharif, B., Li, X., Olesen, J.E., 2018. Root
biomass in cereals, catch crops and weeds can be reliably estimated without considering
aboveground biomass. Agriculture Ecosystem & Environment 251, 141-148.
The project ’Row cropping in organic arable farming for increased productivity and sustainability’ (RowCrop) is a part of the Organic RDD 2- programme, which is coordinated by ICROFS (International Centre for Research in Organic Food Systems). It has received grants from ’Grønt Udviklings- og Demonstrationsprogram (GUDP)’ under the Ministry of Environment and Food of Denmark.