Visualization of Peanut Nodules and Seasonal Nodulation Pattern in Different Tillage Systems Using a Minirhizotron System

Abstract

Nodulation is essential for providing the nitrogen (N) needs of peanut, but little is known about the time course of nodule development with soil depth in a field production system. A minirhizotron system allows for non-destructive, periodic digital imaging of identical locations in the crop root system in situ, including the associated nodules. Because the system allows imaging at the same location over time, individual nodule development and subsequent senescence can be followed throughout the growing season. To test the proof of concept for the use of a minirhizotron system to observe peanut nodule development, a case study was conducted in 2012 in Citra, FL in a sod-based production system managed with both conservation and conventional tillage at two different timings. Images were taken to a soil depth of 90 cm on four dates during the growing season, and nodule number, surface area, and senescence were determined. Most nodules occurred at depths spanning 5-30 cm with very few outside of this range; however, individual nodules were noted as deep as 90 cm. In this case study, tillage operation and timing had no impact on the total number of nodules produced, and the peak seasonal nodule number was formed relatively early in the season (9 July -61 days after planting) and stayed constant until harvest. Nodule number varied by soil depth with the majority of nodules formed in the 0-20 cm depth. Nodule surface area was impacted by tillage type with conservation tillage treatments having larger nodule size (average 2.6 mm 2 ) than nodules in conventional tillage (1.9 mm 2 ). Maximum nodule surface area was achieved by midseason on 1 August. This study gave a unique visual assessment of nodule development for field grown peanut over time and provided data that has rarely been reported. In addition, this study also illustrated that the minirhizotron technique could be successfully utilized in studies examining the development of nodules in peanut and would likely be applicable for similar studies in other legume crops.The nitrogen fixation process in peanut (Arachis hypogaea L.) is essential for providing nitrogen (N) for the crop throughout the season, as it delivers from 50-80% of the total N required by the plant (Boddey et al., 1990)

Automated and estimation methods to count nodule number in common bean

“…Barbedo (2012), that also used digital images, obtained a good correlation between automatic and manual counting (0.91). Using a different approach, but also based on digital images, Gray et al (2013) and Rowland et al (2015) used the minirhizotron technique to assess nodulation in legumes. Gray et al (2013) demonstrated the potential of this technique, already used in the observation of root growth, to understand the dynamic of nodule production and distribution in soil profile within the growing season.…”

“…The estimates generated from minirhizotron for nodule number, density and size were consistent with previously published data for fieldgrown soybean. The use of minirhizotron technique also allowed to study for the first time the nodule formation through the soil profile and across the time in peanut (Rowland et al, 2015). Cardoso et al (2009) found out that most of the nodulation resulting from inoculation occurs at the primary crown root of peanut, soybean and common bean.…”

“…As observed, most of the studies that tried to reduce the labour involved in nodulation evaluation used devices to obtain digital images (Vikman & Vessey, 1993;Lira Junior & Smith, 2000, Lira Junior et al, 2003, 2005Barbedo, 2012, Gray et al 2013, Rowland et al 2015. However, their methods require sophisticated devices and are potentially affected by the uniformity of illumination, the contrast between the nodules and background, etc.…”

“…Also, Barbedo (2012) also used digital images to assess nodule number in legumes after the nodules have been removed from the roots. More recently, some efforts were made to use the minirhizotron imaging technique, a non-destructive procedure that originally allows the study of roots within the soil, to verify nodule development and senescence in soybean (Gray et al, 2013) and peanut (Rowland et al, 2015).…”

Improving cultivation of groundnuts

“…Compared with conventional tillage, conservation tillage showed a reduced incidence of tomato spotted wilt disease of peanut in North Carolina (Hurt, 2006). The nodule size is larger in conservation tillage compared to conventional tillage (Rowland, 2015). In Georgia, the conservation production system increased water-holding capacity of the soil and enhanced soil water conservation (Hawkins, 2016).…”