Compost and organic matter
Quick answer. Organic matter raises both water-holding capacity and cation exchange capacity, which are precisely the two things sandy soil lacks. Use it well decomposed: material with a wide carbon-to-nitrogen ratio temporarily locks up soil nitrogen while it breaks down, so immature compost makes a crop look nitrogen-deficient at exactly the moment you thought you were feeding it.
What organic matter does
FAO is direct on the mechanism: soils rich in organic matter have a higher cation exchange capacity than soils low in organic matter. With sandy soils sitting below 10 cmol/kg against more than 30 for clay, raising organic matter is the main practical route to holding applied nutrients in the root zone rather than losing them below it.
It also raises water-holding capacity, which addresses the other half of the sandy-soil deficit, and supports biological activity — which FAO lists as low in arid soils.
The carbon-to-nitrogen problem
This is the part that catches people out. FAO describes soils whose humus forms are poor in nitrogen with undesirably high C:N ratios, and the same principle applies to material you add. Microorganisms decomposing high-carbon material need nitrogen to do it, and they take that nitrogen from the soil. During that period the crop competes with them and loses.
The visible result is a crop that yellows after an application of organic matter. The grower's natural conclusion is that more is needed. The actual answer is that the material was not finished decomposing. Use mature compost, or apply raw material well ahead of the crop rather than immediately before it.
The Kuwaiti reality
Two constraints from FAO's account of arid conditions apply directly. First, raising soil organic matter is desirable but the possibilities are limited because of high mineralization rates — what you add breaks down faster in heat, so this is an ongoing programme rather than a one-time amendment. Second, the application of organic substances is often limited by competitive use of crop residues for fodder, fuel and other purposes; and FAO states plainly that mulching is difficult in these environments because of a shortage of organic matter. Supply, not technique, is frequently the binding constraint here.
Food safety
Raw manure must not be incorporated into beds for crops eaten raw — lettuce, rocket, the herbs, carrot, radish, beetroot. This is a food-safety rule and it applies regardless of horticultural convenience. Composted, matured material is a different matter from fresh manure.
Compost is not a fertiliser and is not a substitute for analysis. Its nutrient content is variable and unknown unless tested, and imported compost can carry salinity of its own — a real risk in a region where FAO notes occasional excess of soluble salts. Adding compost to correct a suspected deficiency is a guess. Test first. Yellowing after an organic amendment is more often immobilisation than deficiency. A visual symptom alone is not a confirmed diagnosis.
Sources
FAO — Fertilizer and Plant Nutrition Bulletin 16, Chapter 4 (organic matter and CEC), Chapter 5 (C:N ratios; arid soils: low organic matter, high mineralization rates, competitive use of residues), Chapters 3 and 7. Accessed 27 August 2026. No rate or quantity is stated.
Last reviewed 27 August 2026