Very poor soils occur mainly in rainfed lowland and upland systems and limit rice growth because of their very low nutrient content and their low ability to hold nutrients. Their usually low pH causes low nutrient availability to the plant, and toxic levels of iron and aluminum may accumulate in the rhizosphere.

Economic options to improve such soils are limited. It is very important to use of suitable varieties (tolerant to iron/aluminum toxicity) and where transplanting is used, good seedbed management is essential. Other options are:

• Application of organic matter is essential to supply macro and micro nutrients but also to improve water and nutrient holding capacity. In at least temporary flooded fields, organic matter can help to increase the pH but high rates may cause iron toxicity. Application of carbonized organic matter (e.g., charcoal) is an indigenous technology to increase and maintain soil fertility on such soils.

• Low rates of inorganic fertilizer can be profitable (40:26:12 kg NPK per hectare) but the effect should be tested in the field. Application of carbonized organic matter (e.g., charcoal) is an indigenous technology to improve soil fertility on such soils but the positive effect may only appear after several season.

• In upland systems, adequate cropping sequences are the best way to maintain soil fertility.

Plants that lack nitrogen have smaller leaves

• In rainfed lowlands, delay planting until pH has increased sufficiently after flooding (to immobilize Al).

If liming is an option, apply 1-3 tons lime (CaCO3) or dolomite per hectare. Dolomite not only raises the pH but also supplies Mg (which helps to decrease Al toxicity). Otherwise, Mg-fertilizers (e.g., Kieserite or Langbeinite) at 50 kg per hectare can help to reduce Mg deficiency and reduce Al toxicity.