A method to estimate plant density and plant spacing heterogeneity: application to wheat crops
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Liu et al. Plant Methods (2017) 13:38 DOI 10.1186/s13007-017-0187-1
Open Access
METHODOLOGY
A method to estimate plant density and plant spacing heterogeneity: application to wheat crops Shouyang Liu1*, Fred Baret1, Denis Allard2, Xiuliang Jin1, Bruno Andrieu3, Philippe Burger4, Matthieu Hemmerlé5 and Alexis Comar5
Abstract Background: Plant density and its non-uniformity drive the competition among plants as well as with weeds. They need thus to be estimated with small uncertainties accuracy. An optimal sampling method is proposed to estimate the plant density in wheat crops from plant counting and reach a given precision. Results: Three experiments were conducted in 2014 resulting in 14 plots across varied sowing density, cultivars and environmental conditions. The coordinates of the plants along the row were measured over RGB high resolution images taken from the ground level. Results show that the spacing between consecutive plants along the row direction are independent and follow a gamma distribution under the varied conditions experienced. A gamma count model was then derived to define the optimal sample size required to estimate plant density for a given precision. Results suggest that measuring the length of segments containing 90 plants will achieve a precision better than 10%, independently from the plant density. This approach appears more efficient than the usual method based on fixed length segments where the number of plants are counted: the optimal length for a given precision on the density estimation will depend on the actual plant density. The gamma count model parameters may also be used to quantify the heterogeneity of plant spacing along the row by exploiting the variability between replicated samples. Results show that to achieve a 10% precision on the estimates of the 2 parameters of the gamma model, 200 elementary samples corresponding to the spacing between 2 consecutive plants should be measured. Conclusions: This method provides an optimal sampling strategy to estimate the plant density and quantify the plant spacing heterogeneity along the row. Keywords: Wheat, Gamma-count model, Density, RGB imagery, Sampling strategy, Plant spacing heterogeneity Background Plant density at emergence is governed by the sowing density and the emergence rate. For a given plant density, the uniformity of plant distribution at emergence may significantly impact the competition among plants as well as with weeds [1, 2]. Plant density and uniformity is therefore a key factor explaining production, although a number of species are able to compensate for low plant densities by a comparatively significant development *Correspondence: [email protected] 1 INRA, UMR-EMMAH, UMT-CAPTE, UAPV, 228 Route de l’aérodrome CS 40509, 84914 Avignon, France Full list of author information is available at the end of the article
of individual plants during the growth cycle. For wheat crops which are largely cultivated over the globe, tillering is one of the main mechanisms used by the plant to adapt its development
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