Precipitation Patterns Reducing Wheat Yield in Northern Kyushu Since 2000

Abstract

Since 2000, wheat yield per 10 a in Northern Kyushu was about 500 kg in 2007–2008, less than 300 kg in 2010–2011, and about 500 kg again in 2021–2022. Therefore, the effect of climatic conditions on wheat yield in Northern Kyushu was analyzed in detail on a daily basis for 23 years from 2000 to 2022. Three significant weather conditions, namely precipitation from December 10 to 21 and April 12 to 23, and sunshine duration from February 17 to March 1, were adopted as explanatory variables at the 5% level. The standard partial regression coefficients were –0.357 for precipitation from December 10 to 21, –0.433 for precipitation from April 12 to 23, and 0.407 for sunshine hours from February 17 to March 1, with a degree of freedom adjusted multiple correlation coefficient of 0.826 and coefficient of determination of 0.682. Precipitation from December 10–21 decreased the number of ears and grains per square meter, and precipitation from April 12–23 decreased the thousand-grain weight and limited sink size, respectively. Sunshine hours from February 17 to March 1 appeared to be related to sink and source size determination because this is the jointing stage when internode elongation is most active. Avoiding sink size limitation due to precipitation at two specific times of the year, December and April, is important to achieve stable and high yields in wheat in northern Kyushu.