Abstract:
Potassium is the most expensive fertilizer but it is the most important plant nutrient in rice production. Therefore,
series of experiments were conducted at 11 locations (4 in the Kurunegala district and 7 in Polonnaruwa district) with
the objective of investigating yield benefits to addition of K fertilizers. Three potassium fertilizer rates viz.
application of half the recommended rate of K (20 kg K20 ha '), recommended rate of K (40 kg K20 h a1) and no
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addition of K fertilizer (control treatment) were tested with two replicates in each location during 2011 yala and
2011/2012 maha. Treatments having recommended K was applied 20 kg K20 ha 'at basal and 20 kg K20 ha ‘ at 7-14
days before flowering and treatments having half the recommended K was applied 20 kg K20 ha1 at 7-14 days before
flowering. Exchangeable K contents was below 50 mg kg ' in most of the locations but significant yield response to
application of K fertilizer was observed in 1 out of 7 locations in Polonnaruwa and one out of four locations in
Kurunegala in two successive seasons. No significant yield difference between applications of half the recommended
rate of K and recommended rate of K was observed in any of the 11 locations. Significant declining of exchangeable K
contents in soil was not observed even without application of K fertilizer. No clear relationship observed between
exchangeable K content and grain yields. A result of this study revealed that no significant yield improvement to
application of K fertilizer and as such even if half the recommended levels of K is applied that is enough to obtain the
current rice yield levels. Therefore, it can be suggested from this results that studies on long term changes of different
form of K in rice fields is timely needed. It will help to identify an indicator other than exchangeable K to decide the K
requirement of rice to avoid unnecessary application of K fertilizer.
