Improving sandy soil
Quick answer. Sandy soil is short of two things — the ability to hold water and the ability to hold nutrients — and both are addressed by the same lever: organic matter. It is not short of aeration or drainage, which it provides better than clay does. Improvement here is continuous rather than a single job, because organic matter breaks down quickly in a hot climate.
What FAO actually says about sandy soils
The statement is balanced, and worth quoting in full because it corrects a common assumption: sandy soils are generally poor in nutrient reserves and have a low water-holding capacity, but provide favourable conditions for root growth, soil aeration and drainage of surplus water. Clay soils are the reverse — often rich in nutrient reserves and high in water-holding capacity, but with restricted aeration.
So sandy soil is not simply bad soil. It has a specific deficit and a specific strength, and treating it as uniformly poor leads to over-correction — most often by adding so much organic matter or clay that the drainage and aeration advantage is lost.
Cation exchange capacity, in plain terms
Cation exchange capacity is the soil's ability to hold positively charged nutrients — calcium, magnesium, potassium, ammonium — against being washed out. FAO gives the range as less than 10 cmol/kg for sandy soils against more than 30 cmol/kg for clay soils, and states that soils rich in organic matter have a higher CEC than soils low in it.
That is the whole argument for organic matter on sand, in one figure. A soil below 10 cmol/kg cannot retain much of what you apply; applications leach past the root zone. Raising organic matter raises retention, which makes every subsequent application more effective. FAO also gives an ideal ratio of cations on the exchange complex for average mineral soils as roughly 75:15:5–3 of calcium to magnesium to potassium — a target for interpreting an analysis, not a mixing instruction.
The Kuwaiti qualifier
FAO is explicit that in arid conditions an increase in the very low soil organic matter level is desirable, but the possibilities are limited because of high mineralization rates. Organic matter added here decomposes faster than in cooler climates. The practical consequence is that improving sandy soil is a maintenance programme, not a project with an end date — and expectations should be set accordingly.
FAO's arid-soils list also names low biological activity, low available nitrogen owing to low organic matter, phosphate deficiency in sandy soils, and frequent iron and zinc deficiencies caused by fixation under alkaline reaction. Organic matter addresses the first three indirectly. It does not fix the iron and zinc problem, which is a pH and chemistry issue rather than a texture one.
Do not add sand to clay, or clay to sand, on the strength of intuition. Texture change requires very large quantities to achieve anything, and small amounts of the wrong material can make structure worse rather than better. Organic matter is the reliable lever. And test before adding anything: FAO lists occasional excess of soluble salts, adsorbed sodium and boron among arid-soil problems, and an amendment chosen for the wrong problem can compound it.
Sources
FAO — Fertilizer and Plant Nutrition Bulletin 16, Chapter 4 (soil texture and fertility; CEC ranges; organic matter and CEC; cation ratios), Chapter 5 (special problems of nutrient management in arid soils; mineralization rates), Chapters 3 and 7. Accessed 27 August 2026. No rate or quantity is stated.
Last reviewed 27 August 2026