Aboveground vegetation is a poor predictor of root biomass in both annual and perennial crops

Article: Exploring the effects of soil structure, nutrients, and farm management on crop root biomass and depth distribution

Authors: Mattila Tuomas & Häkkinen Laura

Journal: Field Crops Research

Year: 2025

The roots of plants are very important for their growth and for soil carbon sequestration. So how do we ensure that the roots grow well? It is difficult to study them directly because they are hidden underground. That is why root growth and root system size are often estimated from aboveground plant biomass. However, this ignores the variation in root growth caused by soil properties and farm management practices.

This study aimed to identify the main factors explaining variation in root biomass on Finnish farms. The study was carried out on 20 Carbon Action pilot farms in 2021 and 2023. Root biomass was measured in soil samples taken from the farms, from topsoil up to 60–100 cm in the soil depth profile, at 10 cm intervals. Root biomass and depth distribution were compared with soil properties and the farming practices used.

The results showed that root biomass was poorly estimated from the aboveground part of the plant. The ratio of aboveground shoot to roots varied widely. Root biomass depended mainly on soil texture, structure, nutrient availability and history of cultivation practices. The main determinants of root biomass and depth distribution varied between annual and perennial crops. For perennial crops, root growth was more strongly dependent on soil structure than for annuals.

It was also found that 60–70% of the roots were in the topsoil, i.e. the top 0–20 cm, indicating that the topsoil and the roots in it play an important role in soil carbon uptake and nutrient availability for the crop. It also shows the importance of studying roots deeper in the soil.

The results of the study underline the importance of prevention of compaction, maintenance of an appropriate nutrient balance and water management in fields, to enable plants to grow large root systems.

The research was part of the MULTA project of the Carbon Action network.