New Rootsnap Sensor Reveals the Ameliorating Effect of Biochar on In Situ Root Growth Dynamics of Maize in Sandy Soil

Abstract

We investigated if subsoil constraints to root development imposed by coarse sand were affected by drought and biochar application over two seasons. Biochar was applied to the subsoil of pots at 20-50 cm depth in concentrations of 0%, 1%, 2%, and 3% (B0, B1, B2, and B3). Maize was grown in the same pots 1 week and 12 months after biochar application. The maize plants were fully irrigated until flowering; thereafter, half of them were subjected to drought. A new method for observing root growth dynamics and root length density in situ, the Rootsnap sensor system, was developed. The sensors were installed at 50 cm depth just below the layer of biochar-amended subsoil. Using data from a smaller experiment with grass, the calculated root length densities from the sensors were compared with data from scanning of manually washed roots. In year 2, we investigated the effect of aged biochar on root growth using only the root wash and scanning method. The Rootsnap sensor revealed that the arrival time of the first root in B3 at the 50 cm depth averaged 47 days after planting, which was significantly earlier than in B0, by 9 days. The tendency for faster root proliferation in biochar-amended subsoil indicates that biochar reduced subsoil mechanical impedance and allowed roots to gain faster access to deep soil layers. A linear regression comparing root length density obtained from the Rootsnap sensor with the scanning method yielded an r 2 of 0.50. Our analysis using the scanning method further showed that under drought stress, maize roots responded with reduced root diameter and increased root length density at 50-70 cm depth in the first and second year, respectively. The trend under full irrigation was less clear, with significant decrease in root length density for B1 and B2 in year 2. Overall, reduction in subsoil mechanical impedance observed as early arrival of roots to the subsoil may prevent or delay the onset of drought and reduce leaching of nutrients in biocharamended soil with positive implications for agricultural productivity.

Ash and biochar amendment of coarse sandy soil for growing crops under drought conditions

“…As root growth and rhizosphere processes alter soil properties, root development and distribution (in addition to the added biochar and ash) could also have had an impact the observed effects on water retention and evaporation. A positive effect of biochar on in situ root growth in coarse sandy subsoil (same type as used in the present experiment) has also been shown by Ahmed et al (2020), where small cameras (‘root‐snaps’) installed at 50 cm depth showed arrival of maize roots up to 9 days earlier in biochar‐amended subsoil compared to the un‐amended control. The authors ascribed this to reduced mechanical resistance and increased water content in the biochar‐amended subsoil.…”

“…Soil application of biochar (charred biomass) to low‐fertility sandy soils is increasingly been advocated as a means to improve soil fertility and concurrently mitigate climate change by carbon sequestration (Atkinson et al, 2010; Kuppusamy et al, 2016). Coarse sandy soils constitute a large proportion of the cropping and grazing land in the north‐western part of Europe (Ahmed et al, 2020). These soil types are characterized by having a low water holding capacity and by restricted growth of roots due to mechanical impedance of the subsoil.…”

“…Amending coarse sandy subsoil with fine‐grained biochar at appropriate dosage rates has been shown to strongly increase the available water capacity (AWC), while improving both root and shoot growth (Ahmed et al 2020; Bruun et al 2014; Petersen et al 2016; Hansen et al 2016). Such soil fertility improvements could transform coarse sandy soils into being more productive and drought resilient on a long‐term basis due to the recalcitrant nature of biochar, as suggested by Bruun et al (2014).…”

Adaptive pathway of summer maize under drought stress: Transformation of root morphology and water absorption law

“…At this time, rehydration can compensate for the drought effect in the early stage. Through the analysis of root length of different diameter classes, this study (Figure 6) found that the proportion of fine roots of summer maize increases under Frontiers in Earth Science frontiersin.org drought stress, which is consistent with the research of some research scholars (Florian et al, 2019;Ahmed et al, 2020), under appropriate drought stress, the proportion of fine root length and root surface area will increase to strengthen water use efficiency, ensure the formation of a large underground system to support the normal operation of the whole plant, enhance adaptability to adverse environment (Smucker and Aiken, 1992;Lorenc et al, 2018).…”

Spatiotemporal dynamics of soil water-salt and its topographic gradient effects on Alpine area over the Northeastern Tibetan Plateau, China

“…Two quadrants were taken from each sampling site more than 100 m apart, located and recorded using GPS with latitude and longitude, and numbered sequentially according to the order of sampling sites (Wu et al, 2021a). The weeds on the surface were removed, and the soil was extracted using stainless cutting rings (100 cm 3 ) and used to determine the water content of the soil using the oven-drying method at 105 °C and the bulk density of the surface soil (0-10 cm) (Wang et al, 2015;Ahmed et al, 2020). Soil samples were also collected from the surface at a depth of 0-10 cm using a soil auger.…”