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MODELING

A Model to Calculate the Vertical Distribution of Grain Number in Pea

^a Unité d'Agronomie, INRA-INAPG, 78850 Thiverval-Grignon, France
^b Unité de Bioclimatologie, INRA, 78850 Thiverval-Grignon, France

jeuffroy{at}bcgn.grignon.inra.fr

In the pea (Pisum sativum L.) as in most grain legume crops, the seeds are located on the reproductive nodes along the stems. The number of nodes varies widely, and this, combined with variations in environmental conditions during the seed set period, creates a high degree of field-to-field variability in the distribution of seeds along the stems. To model seed number profiles in pea, we adapted a method initially proposed by Dwyer and Stewart for calculating the vertical distribution of plant leaf area in maize (Zea mays L.). The entire profile can be described by two empirical constants, by the number of the individual node bearing the most seeds, and by the maximum number of seeds on one node. These four inputs vary from one location-year to another and are calculated from empirical relationships, taking as explanatory variables the main characteristics of the pea stand. The proposed model simulating seed number per node in pea was evaluated on two samples: one with data from the cultivar used to estimate model parameters (18 points with six different locations and six different years), and another using data from nine other cultivars (27 points). The model gives a reasonable account (r² > 0.80) of the variability in seed number profiles measured in the field. The model uses only one cultivar-dependent parameter (mean weight per seed), and thus it can be easily used by farmers or advisers for practical purposes such as agronomic diagnosis to explain the lack of seeds on some nodes.

Abbreviations: CDD, cumulative degree-days • CGR, crop growth rate • MEP, mean error of prediction • MSEP, mean square error of prediction • NNm, node number with the most seeds in the profile • SNi, seed number on reproductive node i per stem • SNm, maximum number of seeds on one node • SNM2, mean number of stems per m² (branches included) • TRN, total number of reproductive nodes per stem • TSN, total seed number per stem