sampling has been routinely used in field ( Lowe and Wilson, 1974 ) and pot experiments ( Villordon et al., 2009a , 2009b ). In other plant species, non-disruptive methods incorporating rhizotrons and minirhizotrons are routinely used as supplementary or
Arthur Villordon, Don LaBonte and Julio Solis
Li Ma, Chang Wei Hou, Xin Zhong Zhang, Hong Li Li, De Guo Han, Yi Wang and Zhen Hai Han
through glass plates ( Qu and Han, 1983 ; Wang et al., 1997 ). More recently, nondestructive techniques, including rhizotrons and minirhizotrons, have been used to observe the roots in situ and directly through the transparent minirhizotron tubes
Guang Zeng, Stanley Birchfield, Christina Wells and Desmond Layne
Minirhizotrons and specialized camera equipment have been widely adopted for in situ observation of fine root dynamics in horticultural settings. However, the laborious nature of data collection from minirhizotron images limits the number and size of experiments that can reasonably be analyzed. Here we present an algorithm for the automatic detection and measurement of roots in minirhizotron images, including the discrimination of light-colored roots from bright background objects. First, two-dimensional matched filtering and local entropy thresholding are used to produce binarized images from which roots are detected. Next, a strong root classifier based on geometric and intensity features is used to discriminate roots from unwanted background objects. A labeling algorithm identifies each individual root in the image, and root lengths and diameters are measured using Dijkstra's algorithm and the Kimura–Kikuchi–Yamasaki method for obtaining the length of a digitized path. This approach allows us to identify and measure fine roots as individuals, rather than simply measuring the aggregate root length in an image. Experimental results from a collection of 250 peach (Prunus persica) root images demonstrate the effectiveness of the approach. The algorithm is able to detect and measure a variety of roots of different shapes, sizes, and orientations, with a detection rate of 92%, a false–positive rate of 5%, and an average measurement error of 4.1% and 6.8% for length and diameter, respectively. Current work involves improving the efficiency of the algorithm and incorporating it into an application. We are also exploring algorithms for tracking the location of a root over time as it grows darker in color and blends with the surrounding soil.
Dana L. Baumann, Beth Ann Workmaster and Kevin R. Kosola
Erica Ramirez for help with minirhizotron image analysis, Shaminder Miranpuri for assistance with plant growth, and John Stier, Jim Busse, Bjorn Karlsson, and Kay Baergen for comments on the manuscript.
Shengrui Yao, Ian A. Merwin and Michael G. Brown
turnover. Minirhizotron observation tubes enable researchers to observe the same roots repeatedly in situ with minimal disturbance and provide information about root lifecycle, distribution, diameter, and length ( Hendrick and Pregitzer, 1992 ; Reid et al
José A. Franco, Víctor Cros, Sebastián Bañón, Alberto González and José M. Abrisqueta
The influence of two irrigation treatments during nursery production on the post-transplant development of Lotus creticus subsp. cytisoides was studied. The treatments lasted 96 days and consisted of irrigating 2 days/week with a total of 2.3 L of water per plant over the whole nursery period (T-2) or irrigating six days per week with a total of 7 L of water per plant (T-6). T-2 plants had greater root length: shoot length ratio and higher percentage of brown roots, an indicator of more resistance to post-transplant stress. Minirhizotrons revealed more active root growth in the surface soil of the T-2 plants, although the plants of both treatments rapidly colonized the whole soil depth studied (0-160 cm deep). T-2 plants had greater stem length growth per unit of soil area covered.
D.M. Glenn and W.V. Welker
The objective was to determine the interrelationship between root growth and plant available soil water (PAW) for young, nonbearing, and mature fruiting peach trees (Prunus persica L. Batsch) over 7 years. Root growth observed with minirhizotrons indicated that young, nonbearing trees developed new white roots throughout the growing season. The pattern of new white root growth became bimodal when the trees fruited. White root production in mature trees appeared in March, preceding budbreak, ceased in June, resumed following fruitremoval in August, and persisted through January. The appearance of white roots was inversely related to the presence of fruit and was not correlated to PAW levels in the 0 to 90 cm depth. The lack of root growth response to PAW levels was attributed to a root system that penetrated the soil to depths beyond our zone of sampling. Circumstantial evidence suggests that deep roots help maintain the surface root system when the surface soil dries.
J. Roger Harris, Nina L. Bassuk, Richard W. Zobel and Thomas H. Whitlow
The objectives of this study were to determine root and shoot growth periodicity for established Fraxinus pennsylvanica Marsh. (green ash), Quercus coccinea Muenchh. (scarlet oak), Corylus colurna L. (Turkish hazelnut), and Syringa reticulata (Blume) Hara `Ivory Silk' (tree lilac) trees and to evaluate three methods of root growth periodicity measurement. Two methods were evaluated using a rhizotron. One method measured the extension rate (RE) ofindividual roots, and the second method measured change in root length (RL) against an observation grid. A third method, using periodic counts of new roots present on minirhizotrons (MR), was also evaluated. RE showed the least variability among individual trees. Shoot growth began before or simultaneously with the beginning of root growth for all species with all root growth measurement methods. All species had concurrent shoot and root growth, and no distinct alternating growth patterns were evident when root growth was measured by RE. Alternating root and shoot growth was evident, however, when root growth was measured by RL and MR. RE measured extension rate of larger diameter lateral roots, RL measured increase in root length of all diameter lateral roots and MR measured new root count of all sizes of lateral and vertical roots. Root growth periodicity patterns differed with the measurement method and the types of roots measured.
Upendra M. Sainju, Bharat P. Singh, Syed Rahman and V.R. Reddy
The influence of tillage [no-till (NT) vs. moldboard plowing (MP)], cover crop [hairy vetch (Vicia villosa Roth) (HV) vs. no hairy vetch (NHV)], and N fertilization (0 and 180 kg·ha–1 N) on root distribution and growth rate of tomato (Lycopersicon esculentum Mill.) transplants was examined in the field from May to August in 1996 and 1997. Experiments were conducted on a Norfolk sandy loam (fine-loamy, siliceous, thermic, Typic Kandiudults) in central Georgia. Root growth was estimated every 1 to 2 weeks with minirhizotron tubes installed in the plot. Roots were well distributed at soil depths between 1 and 58.5 cm and a maximum root count of 3.14 roots/cm2 soil profile area was found at 19.5-cm depth with MP and no N fertilization in 1996. In general, NT with HV or with 0 kg·ha–1 N increased root proliferation at a depth of 6.5 to 19.5 cm, while MP with 180 kg·ha–1 N increased root proliferation at greater depths. Total root count between 1 and 58.5 cm was not influenced by management practices, but increased linearly at rates of 0.35 roots/cm2 per day from 20 June to 11 July 1996, and 0.03 roots/cm2 per day from 16 May to 5 Aug. 1997. Root growth thereafter was minimal. Because of the higher temperature during early development, growth rate and number of roots were greater in 1996 than in 1997. Superior moisture conservation, accompanied by increased N availability, may have increased root proliferation in the surface soil in NT with HV or with 0 kg·ha–1 N compared with NT with NHV or with 180 kg·ha–1 N, and MP with or without HV or with or without N fertilization. Root growth, however, was not related with aboveground tomato yield.
José A. Franco and Daniel I. Leskovar
Containerized `Lavi' muskmelon [Cucumis melo L. (Reticulatus Group)] transplants were grown in a nursery with two irrigation systems: overhead irrigation (OI) and flotation irrigation (FI). Initially, root development was monitored during a 36-day nursery period. Thereafter, seedling root growth was monitored either in transparent containers inside a growth chamber, or through minirhizotrons placed in the field. During the nursery period, OI promoted increased early basal root growth, whereas FI promoted greater basal root elongation between 25 and 36 days after seeding (DAS). At 36 DAS leaf area, shoot fresh weight (FW) and dry weight (DW), and shoot to root ratio were greater for OI than for FI transplants, while root length and FWs and DWs were nearly the same. Total root elongation in the growth chamber was greater for FI than for OI transplants between 4 and 14 days after transplanting. Similarly, the minirhizotron measurements in the field showed a greater root length density in the uppermost layer of the soil profile for FI than for OI transplants. Overall, muskmelon transplants had greater root development initially when subjected to overhead compared to flotation irrigation in the nursery. However, during late development FI transplants appeared to have a greater capacity to regenerate roots, thus providing an adaptive mechanism to enhance postplanting root development and to withstand transplant shock in field conditions. At harvest, root length density and yield were closely similar for the plants in the two transplant irrigation treatments.