This paper describes a journey which started with the question: why do farmers reapply phosphate? This led to understanding how phosphate and other specifically sorbed ions, both cations and anions react with soil. Under most soil conditions, they do not precipitate to give specific compounds. Rather they are specifically adsorbed onto the surface of soil particles and then penetrate the particles via diffusion mechanisms. The pathways by which they move differ between ion species; for example nickel penetrates the lattice of iron oxides but phosphate penetrates defects between particles. Such reactions change important properties of the soil. Reaction with phosphate conveys negative charge to the reacting surface and so decreases the buffering capacity for phosphate; this makes subsequent phosphate applications more effective. Nor does the diffusive penetration continue unabated; as phosphate builds up, diffusive penetration slows and then virtually stops. These effects mean that on long-term fertilised soils, phosphate fertiliser is much more effective and annual doses (if they are needed at all) should be much smaller. I suggest that failure to appreciate this is the cause of phosphate losses from farmland and consequent pollution of water bodies.

本文描述了一个从以下问题开始的旅程：农民为什么要重新施用磷酸盐？这导致了解磷酸盐和其他特定吸附的离子（阳离子和阴离子）如何与土壤发生反应。在大多数土壤条件下，它们不会沉淀产生特定的化合物。相反，它们被特异性吸附到土壤颗粒表面，然后通过扩散机制穿透颗粒。它们移动的途径因离子种类而异；例如，镍穿透氧化铁的晶格，但磷酸盐穿透颗粒之间的缺陷。这种反应改变了土壤的重要特性。与磷酸盐的反应将负电荷传递到反应表面，因此降低了磷酸盐的缓冲能力；这使得后续的磷酸盐应用更加有效。扩散渗透也不会继续有增无减；随着磷酸盐的积累，扩散渗透减慢，然后几乎停止。这些影响意味着在长期施肥的土壤上，磷肥更有效，年剂量（如果需要的话）应该小得多。我认为未能意识到这一点是导致农田磷酸盐流失以及随之而来的水体污染的原因。