Soil temperature and its association with maize yield variations in the Highlands of Kenya

Abstract

In the Highlands of Kenya every 1-week delay in planting maize after the onset of the rains reduces the grain yield by approximately 0-6 t/ha. No satisfactory explanation has been found for this phenomenon. A physiological growth study was made on four dates of planting per year over 4 years. Early growth rates and maximum crop growth rates showed a progressive decline with delay in planting which resulted in smaller plants at 5 weeks post-emergence and at 50 % tassel emergence in maize planted later. There was a strong relationship between the size of plant at tasselling and the final grain yield and a highly significant relationship (r = 0-94) between the size of plant at 5 weeks post emergence and the final grain yield. Other environmental studies showed that soil temperature at 7-5 cm, coupled with a soil moisture stress factor, largely controlled the dry-matter production rate during early growth, and consideration of the mean value of these two variables over the first 5 weeks of growth accounted for 70 % of the variation of dry matter at 5 weeks post-emergence. It was further shown that 82 % of the variation in final grain yield caused by date of planting could be accounted for by consideration of the mean value of these two variables during the first 5 weeks of growth. account for the pronounced 'time of planting' effect in the Highlands of Western Kenya. He In the tropics it has been widely observed that concluded that low yields of maize planted late maize planted at the onset of the rains gives con-were largely due to a progressive deterioration in siderahly greater yields than later plantings soil physical conditions as the season advanced. (Hemingway, 1955;Goldson, 1963; Akehurst & Furthermore, in an artificial watering trial he Sreedharan, 1965;Allan, 1972). This has become found that increasing amounts of water applied known as the 'time of planting' effect.during the period from planting to 5 weeks postMany varied explanations have been put for-emergence caused corresponding reductions in ward to account for the 'time of planting' effect early growth, number of kernels initiated and final in East Africa. Hemingway (1955) suggested that grain yield. As a result of these experiments, and yields of maize planted late were less because young a study of rainfall distribution patterns, he maize plants were more severely attacked by fun-suggested that poor soil aeration was the most gal leaf diseases than maize planted early, whereas important soil physical factor causing yield reducBirch (1960) suggested that crops planted early tions in maize planted late. However, this hypoyielded more because they were able to take ad-thesis was not based on actual measurements of vantage of the flush of soil nitrogen mineralization soil aeration, and Cooper (1975) recently showed that occurs during the wetting and drying cycles that the aeration status of Kitale soils under at the onset of the rains. In certain areas with short young maize never limits growth, even if the rainy seasons, maize planted late will suffe...

Effects of Seed Size on Growth and Yield of Maize in the Kenya Highlands

“…Previous work at Kitale (Cooper and Law, 1977;Law and Cooper, 1976) suggested that larger plants could more fully realize the grain potential than smaller ones. Later mulch trials, however (Cooper and Law, 1978), showed that an increased yield can occur even when there is no difference in total dry weight at Relative growth rate* (g g" 1 1-3 weeks postemergence Absolute crop growth ratef (g m~a day" 1 ) 59-115 days postemergence…”

“…Later mulch trials, however (Cooper and Law, 1978), showed that an increased yield can occur even when there is no difference in total dry weight at Relative growth rate* (g g" 1 1-3 weeks postemergence Absolute crop growth ratef (g m~a day" 1 ) 59-115 days postemergence…”

“…Since time-of-planting trials show that warmer soils lead to increased crop growth rate (under conditions of full ground cover) and higher yields, and since the present work showed similar crop growth rates leading to similar yields, it would be pertinent to measure rates of growth during the season and to relate them to final yield, rather than absolute sizes at any point. Unfortunately, plot sizes during the mulching trials reported by Cooper and Law (1978) made destructive sampling impossible.…”

“…Due to lodging, only 60 plants of each treatment were harvested from one block, but a second seedsize trial was also run the same year and showed a similar pattern of growth and yield to that presented here. Since this second trial was planted earlier in the season (16 April), seedlings were exposed to more favourable soil temperatures, which have been shown to confer considerable yield advantage (Cooper and Law, 1977). The yields of both trials (Tables 2 and 3) showed little difference due to seed size, with the subsidiary trial giving higher yields.…”

“…Furthermore Cooper and Law (1977) have shown that variations in seedling vigour in the Highlands of Kenya, induced by soil temperature differences, were closely correlated with final grain yield according to the equation: Y= IO-I W 5 + 11-9 (r = o-94) where Y = grain yield (g/plant), and W 5 = plant dry weight at 5 weeks (g/plant).…”