Canadian Shield clay soils are high in potassium (K) reserves. The differential contribution of soil K fractions to crop nutrition is an important issue for ley farming systems of Eastern Canada where nitrogen (N)‐based manure application rate leads to K surplus and redistribution. Our objective was to assess the long‐term change in K offtake, K budget, and K forms under a 3‐yr‐cycle ley farming system (barley [Hordeum vulgare]–mixed forage–mixed forage) initiated in 1989 and ended in 2016. The liquid dairy manure (LDM) supplied higher amounts of K than mineral fertilization (MIN) and led to larger K offtake across crop cycles. The cumulative K budgets averaged −579 kg K ha⁻¹ cycle⁻¹ for MIN and +69 kg K ha⁻¹ cycle⁻¹ for LDM. Despite cyclic variations, topsoil showed a surplus of exchangeable K (>100 kg K ha⁻¹) at the end of experimentation under MIN and LDM compared to the initial state in 1989. Exchangeable and non‐exchangeable K fractions increased between 2001 and 2016 in 0‐ to 30‐cm depth even under K deficit (MIN), due to K release from slowly available forms and recycling from lower layers. There were no significant relationships between K budget and exchangeable K down to 90 cm. The approach relating soil exchangeable K and K budgets to support buildup and maintenance of soil fertility proved to be inappropriate in clay soils high in illite‐like minerals. Potassium dynamics in clay soils under ley farming highlighted the importance of considering non‐exchangeable and subsoil K in K fertilization recommendations.

中文翻译：

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长期实验中钾平衡条件下钾肥在黏土中的转化

加拿大盾构粘土的钾（K）储量很高。对于加拿大东部的养牛业系统来说，土壤钾组分对作物营养的不同贡献是一个重要的问题，在该系统中，基于氮（N）的肥料施用量导致钾肥过剩和再分配。我们的目标是评估1989年启动并于2016年结束的3年周期的ley耕作制度（大麦[ Hordeum vulgare ]-混合饲料-混合饲料）下钾素吸收量，钾素预算和钾素形态的长期变化。。液态奶牛粪（LDM）提供的钾量高于矿物肥料（MIN），并导致整个作物周期吸收更多的钾。MIN的累计K预算平均为-579 kg K ha ^-1周期^-1，+ 69 kg K ha ^-1周期^-1用于LDM。尽管存在周期性变化，与1989年的初始状态相比，在MIN和LDM条件下试验结束时，表土仍显示出过量的可交换K（> 100 kg K ha ^-1）。2001年至2016年间，可交换和不可交换K分数增加。甚至在K亏缺（MIN）的情况下，深度仍为0至30 cm，这归因于K从缓慢可用的形态中释放出来以及从较低的层中回收。K预算和90厘米以下可交换K之间没有显着关系。在伊利石样矿物质含量高的粘土土壤中，将土壤可交换的钾和钾预算用于支持土壤肥力的建立和维持的方法被证明是不合适的。耕作条件下粘土土壤中钾的动态变化突出了在钾肥推荐中考虑不可交换的钾和下层土壤钾的重要性。