Évaluation de la stabilité du rendement fourrager et de la dynamique du potassium et du phosphore dans un Gleysol humique de l'Est du Canada
|Advisor:||Parent, Léon-Étienne; Ziadi, Noura|
|Abstract:||A stable supply of forages is important to ensure sustainability of the dairy farms in Eastern Canada. In addition to nitrogen, optimal forage growth requires an adequate supply of potassium (K) and phosphorus (P), whose availability could be influenced by agricultural practices. The main objective of this thesis was to assess forage yields stability under contrasting management practices, but also to understand how these practices influence K and P dynamics in clayey soils of Eastern Canada. We used along-term experiment established in 1989 in the region of Saguenay Lac St-Jean. This was a fixed barley-forage-forage rotation established on a humic Gleysol under moldboard plow (MP) or chisel (CP) plowing and supplied by mineral (MIN) or organic (liquid dairy manure, LDM) fertilizers. We found that crop yields were more stable cyclically (per three-year cycle) than annually. Yield stability index was reduced by factor of 1.86 ± 0.57 for grains, 1.87 ± 0.24 for straw and 2.00 ± 0.25 for forage using cyclic assessment. The LDM returned higher forage and straw yields than MIN. However, yields were not influenced by the tillage practice. Cumulative K budget averaged −579 kg K ha⁻¹ cycle⁻¹ with MIN and +69 kg K ha⁻¹ cycle⁻¹ with LDM. Exchangeable K accumulation in upper soil layers was higher with LDM than MIN. Nevertheless, no significant relationship between cumulative K budget and exchangeable K was observed across cycles. Exchangeable and non-exchangeable K fractions between 2001 and 2016 increased under MIN (deficit K budget), underlying the dynamic equilibrium between soil K forms. For P, cumulative cyclic budget varied from –20 to +150 kg P ha⁻¹ with LDM, and –33 to +3 kg P ha⁻¹ with MIN, while higher reserves of Mehlich-3 P were measured in topsoil (0–15 cm) with MIN than LDM. The negative relationship between cumulative P budget and Mehlich-3 P highlighted the complex mechanisms controlling soil P availability. Soil analysis in 0–15 cm layer showed lower total P with LDM than MIN for two dates (2001 and 2016), and a decline of organic P between 12 and 27 years under LDM probably due to organic P mineralization or loss. Tillage practices had significant effect on soil K and P distribution. Due to the difference in plowing depth between CP (15 cm) and MP (20 cm), the CP led to greater K and P accumulation than MP in the 0−15 cm layer, while the reverse was observed in 15−30 cm layer. The results also indicated that K and P uptakes by plants occurred in the 15−30 cm depth. Overall, this study showed that cyclic yield stability opened up a new perspective for land allocation and forage storage, and underlined the high buffer capacity in K and P of fine-textured soils. With regular monitoring of crops, and soil K and P status, CP and LDM could ensure the sustainability off orage production systems in Eastern Canada. However, the approach relating K and P budget to their available forms to support soil fertility buildup and maintenance appeared to be wrong in this clayey soil. Finally, we suggest to revisit local fertilization strategy of forage legume and grass mixtures in rotation with cereal established on a humic Gleysol in order to include non-exchangeable K content in K fertilizer recommendation and soil clay content in P fertilizer recommendation.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||14 June 2021|
|Collection:||Thèses et mémoires|
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