Yoshida - 1981 - Fundamentals of Rice Crop Science

NUTRITIONAL DISORDERS 193
nitrogen or potassium fertilizers are applied only as basal dressings. Such soils
also often have a low active iron content and are called degraded paddy soils.
Bronzing, Akagare Type I, and Akiochi are related. All these disorders occur on
sandy or silty soils low in cation exchange capacity and active iron. Small
differences in soil characteristics, such as pH, organic matter, potassium content,
degree of drainage resulting from physiographic changes, and varietal characters
may determine the type of disorder.
Calcareous soils have a pH above 7 and the availability of elements such as
phosphorus, iron, and zinc is low, leading to the corresponding deficiencies.
Potassium deficiency may also occur if the soil is low in this element.
Soils high in sodium generally have a high pH and total soluble salts. Plants on
these soils frequently suffer from a salinity problem and sometimes from iron
deficiency and boron toxicity.
In neutral soils, the availability of nutrients is just adequate and deficiencies or
excesses of nutrients are unlikely to occur. However, if a soil is low in an essential
nutrient, plants may suffer from a deficiency.
On peaty soils, copper deficiency is suspected as a major nutritional problem
(Driessen 1978). Copper deficiency is also suspected to cause Branca in Portugal.
These two problems, however, require further clarification.
In addition to inherently deficient soil environments, a shift in the fertilizer
industry from ammonium sulfate to high-analysis nitrogen fertilizers and from
superphosphate to concentrated phosphates appears to be triggering the increased
incidence of sulfur deficiency in lowland rice.