Potassium nutrient response in the rice-wheat cropping system in different agro-ecozones of Nepal

Most of the soils of Nepal had a higher potassium (K, expressed as K2O) level inherently. Later in 1976, the Government of Nepal has recommended K fertilizer rate at 30 kg K2O ha(-1) in rice-wheat cropping systems. However, those crops began showing K deficiency symptoms in recent decades, which could be due to a large portion of soils with depleted K level or the insufficient input of K fertilizer for crop production. This study explored a limitation of K nutrient in the crops by establishing field trials from 2009-2014 at three agro-ecozones i.e., inner-Terai (2009-2010), high-Hills (2011-2012), and Terai (2012-2014) in Nepal. Seven rates of K fertilizer at 0, 15, 30, 45, 60, 75, and 90 kg K2O ha(-1) were replicated four times in a randomized complete block design, where crop yields and yield-attributing parameters of rice-wheat cropping system were recorded. Results revealed that an increase in K rates from 45 to 75 kg K2O ha(-1) under inner-Terai and Terai conditions and 45 to 60 kg ha(-1) under high-Hills conditions produced significantly higher grain yields compared to the recommended K dose. Economically, the optimum rate of K fertilizer should not exceed 68 kg K2O ha(-1) for rice in all agro-ecozones, or 73 kg K2O ha(-1) for wheat in inner-Terai and 60 kg K2O ha(-1) for wheat in high-Hills and Terai. Our findings suggest to increase potassium application in between 1.5 to 2.5 times of the current K fertilizer rate in rice-wheat cropping system of Nepal that need to be tested further in different locations and crop varieties.

Automated summary

The soils of Nepal have naturally high potassium levels, but recent studies have shown deficiencies in potassium levels in rice and wheat crops, especially in the inner-Terai and Terai regions. Increasing potassium fertilizer application rates beyond recommended levels significantly improved grain yields, suggesting a need for increased potassium application rates in the rice-wheat cropping system in Nepal.