DOI: 10.7910/dvn/gdqbq1
title: Data on impact of soil compaction, drought and their combination on vertical root distribution, morphological traits, and soil water patterns in Urochloa hybrids

description: Urochloa grasses are typically grown in rain-fed systems, where soil compaction and water limitation (drought) significantly reduce their productivity. Deep roots are a key trait in these grasses, allowing them to access water from soil layers at depth during droughts, which helps to prevent water stress (Cardoso et al., 2015). However, soil compaction may limit the ability of roots to penetrate deeply, restricting water uptake and increasing vulnerability to drought. This dataset describes the impact of four soil conditions (control, compaction, drought, and a combination of compaction and drought) on five Urochloa hybrids grown under greenhouse conditions. It includes measurements of root dry mass distribution at 10 cm intervals down a 100 cm soil column, D95 (the depth at which 95% of root mass is concentrated), root morphological traits (number, diameter, and porosity), and shoot dry mass. The data includes information on volumetric water content throughout the soil profile. Such data is not available for Urochloa hybrids or other tropical grasses, making it a valuable tool for understanding their stress responses, water uptake and guiding breeding efforts for more resilient varieties. The data can be used in plant ideotyping and functional structural modelling of roots under various soil conditions to support the development and breeding of more resilient Urochloa hybrids to edapho-climatic stresses such as soil compaction, drought and the combination of both.
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Methodology: Plant material, site description, and experimental design: The hybrids utilized in this study were developed through the interspecific breeding program at the International Center for Tropical Agriculture (CIAT). The hybrids included Mulato 2, Br02-1752, Br12-3868, Br12-2360, and Br12-3659. The soil used in this experiment was a Mollisol collected from CIAT (latitude: 3°60′N; longitude: 76°31′W; altitude: 990 m) at a depth of 0–20 cm. After collection, the soil was sieved through a 0.02 cm mesh, resulting in a loamy-clay texture with a pH of 7.7. Plants were propagated from vegetative propagules following the method described by Cardoso et al. (2015) and were cultivated under greenhouse conditions at CIAT. Environmental conditions included an average temperature of 28/20 °C (day/night), relative humidity of 71/90% (day/night), and a maximum photosynthetic active radiation (PAR) of 1047 µmol m² s⁻¹. Two soil bulk densities (BD, g/cm³) were established to simulate different levels of soil compaction: 1.3 g/cm³ for non-compacted soil and 1.6 g/cm³ for compacted soil (Rivera et al., 2019). Irrigated plants were maintained at 80% field capacity by weighing soil cylinders weekly and adding water equal to the mass lost through evapotranspiration. For drought conditions, watering was discontinued at the onset of the experiment. The experimental design was a completely randomized 2×2×5 factorial arrangement with four replicates, encompassing two compaction levels (non-compacted, compacted) and two irrigation levels (irrigated, drought) across five genotypes (Mulato 2, Br02-1752, Br12-3868, Br12-2360, Br12-3659). Harvest, vertical root distribution, and root morphological traits: Plants were harvested 21 days after the initiation of treatments. Shoots were cut and oven-dried to determine shoot dry mass. Soil cylinders were segmented into ten 10-cm layers, and roots were washed to remove soil. Roots from the uppermost 10 cm were used for morphological analyses, including root number, root diameter, and root porosity. Root number was determined as the total count of main roots. Root diameter was measured on ten nodal roots at three equidistant points along their length using a digital micrometer. Root porosity was assessed on the same roots using the pycnometer method, which estimates the air volume within the root structure (Jensen et al., 1969). After morphological traits were recorded, the dry mass of roots from each 10-cm layer was determined. Cumulative root mass distribution (%) was calculated, and D95 (the depth where 95% of root mass is located) was derived through linear interpolation. Volumetric determination of soil moisture along the soil profile: Before root washing, volumetric soil moisture (m³ m⁻³) was measured every 10 cm of depth using a capacitance-based sensor (ML3 ThetaProbe connected to a HH2 datalogger, Delta-T Devices). Measurements were taken twice per soil profile and scaled to align with the wilting point and field capacity previously determined for each compaction condition