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Analysis and modelling of soil surface crusting and crop emergence. Contribution to the improvement of the SIMPLE model

Abstract : The SIMPLE model can predict the emergence of various types of crop. It includes an empirical module predicting seedling emergence from under a crust. That module is based on the observation of the emergence of sugar beet crops in a field network with silt loam soils. This module is basic, but effective, and the purpose of this work is to allow the extension of forecasts to other sowing conditions and other crops (seedbed types, soil types, different characteristics of the seeds), given the huge problems in crop emergence resulting from the formation of crusts on the surface of seedbeds for various crops. Field experiments were carried out to characterize the different tactics used by the seedlings to break through (penetration, rupture and passage through cracks), according to the different types of crust, in the case of spring (sugar beet, flax and bean) and autumn crops (wheat). On the same plots, we characterized the dynamics of crust formation for the various initial states of seedbeds (aggregate size, soil water content) according to the rains cumulated since sowing. We also analysed soil crusting data acquired on a long term experiment, thus complementing our two experimentation campaigns. The crusts were characterized by their stage, their thickness and their resistance to penetration. Various quantities of cumulated rains, from 11mm for seedbeds mainly made of thin dry earth to 27mm for coarse soil surfaces, were determined in order to obtain the formation of structural crusts, which are already enough to penalize emergence if they dry out. Complementary experiments were led in the laboratory in order to obtain under simulated rainfalls more advanced stages of crust unobserved during the two years of experimentation in the field, and characterize them. We quantified the evolution of the forming network of cracks according to the degree of degradation and the moistening/desiccation alternation. Those data made it possible to parameterise and test geometrical models for the appearance of cracks. The forces exerted by the seedlings and their changes in time, according to the variations in the seed mass, the varieties and the species studied, were measured with force sensors in the laboratory. All those elements made it possible to build a new module integrating factors which had not been taken into account before when predicting emergence through crusts. This module integrates initial states for various seedbeds (structure and water content) and different cumulated rain values which lead to successive stages in the formation of the crust. With each type of crust, a characteristic distribution of resistances is associated. The maximum force of every seedling that comes to the surface is drawn at random in a distribution, then decreases with the age of the seedling. That value is compared day after day with the resistance of the material via a coefficient that makes it possible to determine whether the seedling will emerge or not. That coefficient results from an adjustment to the data observed. It was based on sugar beet, a crop for which numerous and precise data were recorded. The first simulations carried out with this new module show the importance of the effects of the initial states of the seedbeds on emergence rates. The effect of force differences due to the mass of the seeds is more limited (about 10% on average) but it reaches about 20% in certain sowing conditions. We also tested the possibility of using this coefficient for other crops, the force of which had been measured. The extension to other species gives encouraging results but requires additional work. We finally discuss the possibility of using various parameters measured on soils in the laboratory in order to be able to adapt the proposed model to other soil types.
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Submitted on : Wednesday, July 4, 2007 - 8:00:00 AM
Last modification on : Sunday, May 31, 2020 - 2:44:02 AM
Long-term archiving on: : Tuesday, September 18, 2012 - 1:00:51 PM


  • HAL Id : pastel-00002660, version 1



Aude Gallardo-Carrera. Analysis and modelling of soil surface crusting and crop emergence. Contribution to the improvement of the SIMPLE model. Sciences of the Universe [physics]. INAPG (AgroParisTech), 2006. English. ⟨NNT : 2006INAP0029⟩. ⟨pastel-00002660⟩



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