Multielectrode geoelectrical tomography for the quantification of plant roots

The amount and spatial distribution of plant roots are crucial ecological features, and methods based on soil electrical resistivity (r) tomography (ERT) have been proposed for their non-destructive measurement. ERT allows to map root systems in conditions where the contrast of ρ between soil and roots is high, but the electrical behaviour of resistive or heterogeneous soils may interfere with root-borne effects and requires investigation. We studied the spatial distribution of ρ in different soil-root conditions to test the hypothesis that ERT would allow to detect the spatial distribution of plant roots even when low contrast between roots and background soil variation was expected. High-resolution 2-D and 3-D DC (Direct Current) soil resistivity tomograms were used to compare areas of high and low vegetation density in containers where bare soil (LM), was compared to a Medicago sativa L. (HM) stand, and in resistive soils where a stand of Arundo plinii Turra (HA) was compared with a bare soil (LA) and the area under the canopy of Olea europaea L. (HO) was compared with interrow areas (LO). Destructive measurements of root biomass per unit soil volume (RD), soil electrical conductivity (EC), stone content (S) and water content (q) were made in all treatments. Soil resistivity was significantly affected by vegetation density, with a resistive response in HM, HA and HO. The response was related to RD with significant univariate relationships and the spatial pattern of soil resistivity was dominated by roots and other resistive features like stones in all soils. This allows to conclude that ERT is able to detect plant-root effects even in the presence of a resistive background but resistive features interfere with the mesasurements and need to be taken into account. Abbreviations: ρ = in-situ soil electrical resistivity; EC = electrical conductivity of soil samples; θ = volumetric water content; RD = root biomass per unit soil volume; ERT = electrical resistivity tomography; 2-D = Two-dimensional; 3-D = three-dimensional; DC = Direct Current

A novel low-cost open-hardware platform for monitoring soil water content and multiple soil-air-vegetation parameters

Monitoring soil water content at high spatio-temporal resolution and coupled to other sensor data is crucial for applications oriented towards water sustainability in agriculture, such as precision irrigation or phenotyping root traits for drought tolerance. The cost of instrumentation, however, limits measurement frequency and number of sensors. The objective of this work was to design a low cost "open hardware" platform for multi-sensor measurements including water content at different depths, air and soil temperatures. The system is based on an open-source ARDUINO microcontroller-board, programmed in a simple integrated development environment (IDE). Low cost high-frequency dielectric probes were used in the platform and lab tested on three non-saline soils (ECe1: 2.5 < 0.1 mS/cm). Empirical calibration curves were subjected to cross-validation (leave-one-out method), and normalized root mean square error (NRMSE) were respectively 0.09 for the overall model, 0.09 for the sandy soil, 0.07 for the clay loam and 0.08 for the sandy loam. The overall model (pooled soil data) fitted the data very well (R2 = 0.89) showing a high stability, being able to generate very similar RMSEs during training and validation (RMSE(training) = 2.63; RMSE(validation) = 2.61). Data recorded on the card were automatically sent to a remote server allowing repeated field-data quality checks. This work provides a framework for the replication and upgrading of a customized low cost platform, consistent with the open source approach whereby sharing information on equipment design and software facilitates the adoption and continuous improvement of existing technologies

Fodder Yield, Quality and Growth of Chia (Salvia hispanica L.) as Affected by Sowing Density and Top-Dressing Nitrogen Fertilization

Chia (Salvia hispanica L.) seeds are considered a superfood, but research on vegetative biomass uses is scarce. We conducted a two-year trial under the hypothesis that short-day flowering black chia would provide quality forage at high latitudes and tested sowing density (D1 = 125, D2 = 25, D3 = 8 and D4 = 4 plants m(-2)) and top-dressing N fertilization (N = 0, N = 20 kg ha(-1)) at three stages (EV = early vegetative, LV = late vegetative and EF = early flowering). Forage yield reached 9.0 and 5.64 t ha(-1) of total and 2.07 and 1.56 t ha(-1) of leaf dry mass at EF in 2013 and 2014, respectively. High plant density corresponded to higher biomass but to lower plant relative growth rate, stem diameter, branching, proportion of leaves and lipid and crude protein content. Crude protein declined from 18% at EV to about 8% at EF and was lower in D1 than in D4. Lipids ranged between 33.83 g kg(-1) (D4, EV) and 17.34 g kg(-1) (D1, EF) (p &lt; 0.005). N topdressing affected forage quality but not yield. Alpha-linolenic acid was the most abundant fatty acid (FA) (608 g kg(-1) FA at EV). The long vegetative growth of short-day flowering chia in southern Europe is favorable to fodder production, and management should be optimized by seeking balance between growth rate and stand density while optimizing vegetative stage growth for the highest forage quality

In situ detection of tree root distribution and biomass by multielectrode resistivity imaging

Traditional methods for studying tree roots are destructive and labor intensive, but available nondestructive techniques are applicable only to small scale studies or are strongly limited by soil conditions and root size. Soil electrical resistivity measured by geoelectrical methods has the potential to detect belowground plant structures, but quantitative relationships of these measurements with root traits have not been assessed. We tested the ability of two-dimensional (2-D) DC resistivity tomography to detect the spatial variability of roots and to quantify their biomass in a tree stand. A high-resolution resistivity tomogram was generated along a 11.75 m transect under an Alnus glutinosa (L.) Gaertn. stand based on an alpha- Wenner configuration with 48 electrodes spaced 0.25 m apart. Data were processed by a 2-D finite-element inversion algorithm, and corrected for soil temperature. Data acquisition, inversion and imaging were completed in the field within 60 min. Root dry mass per unit soil volume (root mass density, RMD)was measured destructively on soil samples collected to a depth of 1.05 m. Soil sand, silt, clay and organic matter contents, electrical conductivity, water content and pH were measured on a subset of samples. The spatial pattern of soil resistivity closely matched the spatial distribution of RMD. Multiple linear regression showed that onlyRMDand soilwater content were related to soil resistivity along the transect. Regression analysis of RMD against soil resistivity revealed a highly significant logistic relationship (n = 97), which was confirmed on a separate dataset (n = 67), showing that soil resistivity was quantitatively related to belowground tree root biomass. This relationship provides a basis for developing quick nondestructive methods for detecting root distribution and quantifying root biomass, as well as for optimizing sampling strategies for studying root-driven phenomena

Root and Shoot Growth of a Modern and an Old Tall Durum Wheat (Triticum durum Desf.) Variety under Dual-Purpose Management

In dual-purpose cereal systems, the co-production of fodder and grain can increase farm profitability and reduce farming risks. Our work evaluated shoot and root growth in durum wheat (Triticum durum Desf.) under dual-purpose management in a medium-high rainfall area of southern Italy. We compared a modern variety (Core) with a tall ancient variety (Saragolle lucana) under traditional (NDP) and dual-purpose (DP) management and tested the hypothesis that clipping plants during the vegetative stage would reduce root growth and dewatering before anthesis, which is advantageous in drought-prone environments. Experiments were conducted in Bella (PZ), Basilicata region, southern Italy (40 degrees 42 ' N, 15 degrees 32 ' E) on a clay loam soil in 2021 in a split-plot design on 2 x 2 main plots and 1 x 2 split-plots with 6 replicates. The DP treatment consisted of simulated grazing by clipping plants at 5 cm from the ground 3 months after sowing (at first hollow stem). Forage Biomass was not different at p = 0.05 between varieties, with an average of 0.58 t ha(-1) DM. Grain yield was not penalized by clipping (p = 0.05) and did not differ significantly between varieties. SPAD was always lower in the Saragolle variety and lowered by clipping. Defoliation delayed phenology in both cultivars but did not reduce the final number of spikes per square meter. Stomatal conductance was correlated to temperature, did not differ between cultivars, and was not influenced by clipping. Soil water depletion was monitored in modern wheat from the booting stage to the beginning of grain filling. Clipping did not result in a reduction in pre-anthesis water depletion, possibly due to evaporative losses. Root density was markedly reduced by clipping in core variety between 0.20 and 0.60 m and much less in Saragolle. Unclipped Saragolle produced thicker roots and higher root masses compared to clipped plants. Defoliated Saragolle shifted to finer roots, reducing root mass more than length. This may have reduced the metabolic cost of soil exploration, thereby increasing root foraging efficiency

Effect of sowing density and nitrogen top-dress fertilisation on growth and yield of chia (Salvia hispanica L.) in a Mediterranean environment: first results

The demand for sources of nutraceuticals has led to the rediscovery and diffusion of traditional crops such as chia (Salvia hispanica L.), whose leaves and fruits are rich in W3 fatty acids and anti-oxidants. Chia originates in Central America but it is rapidly expanding to new areas. A field experiment conducted at Atella in Basilicata (Southern Italy) was set up to test the response of chia to N top-dress fertilisation (0 and 20 kg ha–1) and to sowing density (D1=125, D2=25, D3=8 and D4=4 plants m–2) in a split-plot design with three replications. First results show maximum leaf area index values up to 7.1 and fresh vegetative biomass production at early flowering ranging between 50.87 (D4) and 59.71 (D1) t ha–1. Yield increased with plant density: a significantly (P<0.01) higher production (398 kg ha–1) was reached in D1. N top-dressing had a detrimental effect on yield and corresponded to higher lodging and lower maturation percentage of seeds, though non-significant. Based on our first results it seems worthwhile to continue agronomical trials for chia in herbaceous systems of southern Italy for leaf production based on traditional genotypes, while fruit production might be pursued by adopting high sowing density and the search for longer-day genotypes

Root and Shoot Growth of a Modern and an Old Tall Durum Wheat (Triticum durum Desf.) Variety under Dual-Purpose Management

In dual-purpose cereal systems, the co-production of fodder and grain can increase farm profitability and reduce farming risks. Our work evaluated shoot and root growth in durum wheat (Triticum durum Desf.) under dual-purpose management in a medium-high rainfall area of southern Italy. We compared a modern variety (Core) with a tall ancient variety (Saragolle lucana) under traditional (NDP) and dual-purpose (DP) management and tested the hypothesis that clipping plants during the vegetative stage would reduce root growth and dewatering before anthesis, which is advantageous in drought-prone environments. Experiments were conducted in Bella (PZ), Basilicata region, southern Italy (40&deg;42&prime; N, 15&deg;32&prime; E) on a clay loam soil in 2021 in a split-plot design on 2 &times; 2 main plots and 1 &times; 2 split-plots with 6 replicates. The DP treatment consisted of simulated grazing by clipping plants at 5 cm from the ground 3 months after sowing (at first hollow stem). Forage Biomass was not different at p = 0.05 between varieties, with an average of 0.58 t ha&minus;1 DM. Grain yield was not penalized by clipping (p = 0.05) and did not differ significantly between varieties. SPAD was always lower in the Saragolle variety and lowered by clipping. Defoliation delayed phenology in both cultivars but did not reduce the final number of spikes per square meter. Stomatal conductance was correlated to temperature, did not differ between cultivars, and was not influenced by clipping. Soil water depletion was monitored in modern wheat from the booting stage to the beginning of grain filling. Clipping did not result in a reduction in pre-anthesis water depletion, possibly due to evaporative losses. Root density was markedly reduced by clipping in core variety between 0.20 and 0.60 m and much less in Saragolle. Unclipped Saragolle produced thicker roots and higher root masses compared to clipped plants. Defoliated Saragolle shifted to finer roots, reducing root mass more than length. This may have reduced the metabolic cost of soil exploration, thereby increasing root foraging efficiency