Speaker
Description
Introduction
In France, phosphorus (P) and potassium (K) fertilizer deliveries have declined since 1990, and stabilized at a relatively low level since 2010. This current situation is the consequence of, on the one hand, the continuing rise in energy prices which is affecting fertilizer prices and, on the other hand, a general reduction in phospho-potassium fertilization of agricultural plots nationwide following fertilization optimization. The aim of this study was to estimate the spatial variability of pH and P, K and Mg content in topsoil of cultivated soils on a national scale, and to identify trends over the period 1990-2020.
Material and methods
In France, since 1990, the National Soil Test database “Base de Données des Analyses de Terre” (BDAT, coordinated by Info&Sols unit, INRAE Orléans) has brought together the results of soil tests of cultivated topsoil carried out throughout mainland France, at the request of farmers in order to manage soil chemical fertility, by laboratories approved by the Ministry of Agriculture. This database contains over 3 million P determinations and an equivalent number of exchangeable K and magnesium (Mg) determinations. Concerning P, three methods of analysis are currently used in France. Thus a pedotransfer function has been used to harmonize the values, which are then expressed in P-Olsen equivalent (Hu et al., 2021). The precise location of the plots remained unknown and only the municipality from where the samples came from was recorded. Statistical parameters (i.e. median, quartiles) were derived from the distribution of soil test values by spatial entities of aggregation. These data were then mobilized as part of a spatio-temporal diagnosis to provide information on the trends of these four fertility parameters over the period 1990-2020. Changes in the availability of these elements for crops was estimated following an agronomic diagnosis using the RegiFert approach (Denoroy et al., 2004).
Results
General trends in the evolution of agricultural soils in mainland France show an increase in pH and Mg content, and a decrease in K, but especially P, content. The spatial distribution of exchangeable P Olsen, K and Mg contents in soils seems to depend mainly on soil characteristics (texture, mineralogical nature of parent materials). The temporal trends observed for Olsen P and exchangeable K, on the other hand, seem to depend on economic factors (rising energy and fertilizer prices), the presence or absence of livestock farming, and recommendations for lower dose calculations as part of a rational fertilization approach. Changes in available P K and Mg contents has a limited impact of fertility classes (3 classes: low, intermediate and high fertility).
Discussion
As change in soil fertility classes is limited, we can argue that changes in cation contents do not have major impact on evolution of recommendations on fertilization in France, until now. However, trend in chemical fertility outlined over the last thirty years are in line with trends in elements contents: decreases in P and K, increases in Mg. This calls for vigilance in the case of P and K, and justify the monitoring of mineral balances on agricultural plots, as well as a policy of regular, reasoned analytical monitoring of soils.
References
Denoroy, P., Dubrulle, P., Villette, C., Colomb, B., Fayet, G., Shoeser, M., Pellerin, S., Pellerin, F., Boiffin, J., 2004. RegiFert, interpréter les résultats des analyses de terre, Techniques et pratiques. INRA, Paris.
Hu, B., Bourennane, H., Arrouays, D., Denoroy, P., Lemercier, B., Saby, N.P.A., 2021. Developing pedotransfer functions to harmonize extractable soil phosphorus content measured with different methods: A case study across the mainland of France. Geoderma 381, 114645. https://doi.org/10.1016/j.geoderma.2020.114645
| Keywords | soil test; spatio-temporal trends;phosphorus;pH;magnesium |
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