ScienceAsia 32 (2006): 151-158 |doi: 10.2306/scienceasia1513-1874.2006.32.151

The Effect of Straw, Stubble and Potassium on Grain
Yield of Rice in Rice-Rice Cropping Systems in the
Mid-Country Wet Zone of Sri Lanka

Senaratne L. Ranamukhaarachchi^* and Willoram Mudiyanselage Ratnayake

 
ABSTRACT: Rice straw is rich in potassium (K). Application of rice straw is encouraged to recycle K in rice soils. In this aspect the importance of rice stubble for increasing soil fertility has not been given due attention. Most of the rice farmers have a multitude of uses of rice straw and hence are reluctant to return straw to the rice fields. Thus, despite extensive and expensive promotions, many rice farmers continue to remove straw and apply K nutrient to their rice crop. Therefore, this study was conducted with the objective of investigating the yield and economic benefits of addition of straw and K fertilizers in the presence of stubble of the preceding rice crop in rice-rice cropping systems in the mid-country wet zone of Sri Lanka.

          Six straw-stubble-potassium combinations and the farmers’ practice were tested in parallel experiments with two common rice age groups (viz. 90- and 105-day), in a randomised complete block design with three replicates during 1996-1997 in the district of Kandy, Sri Lanka. Grain yield and its components, straw and stubble dry weight, harvest index, gross and net income were assessed. The farmers’ practice of applying half the recommended rate of K (8.5 kg K/ha) 7-14 days before flowering in the presence of the stubble of the preceding rice crop gave the highest grain yields of 3.82 and 4.78 t ha^-1 for 90-day and 105 day rice varieties, respectively. These yields were significantly greater than that of the control treatment that received rice straw and stubble only, but not significantly different from the treatment receiving both straw and 17 kg K/ha in the presence of stubble. The application of K fertilizer showed increases in the number of filled grains per panicle (significant in 90 –day rice only) and grain weight (not significant), which collectively increased grain yield and net income compared to control. The farmers’ practice of using half the recommended dose of K (8.5 kg/ha) prior to flowering offered higher yields and net returns compared to the control treatment having straw returned to the rice field in the presence of stubble of the preceding rice crop.

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Agricultural Systems and Engineering, School of Environment, Resources and Development, Asian Institute of Technology, Thailand.

* Corresponding author, E-mail: ranamuka@ait.ac.th & ranamuka@yahoo.com

Received 18 Jul 2005, Accepted 4 Jan 2006