Yield and quality of large-seeded type peanuts as affected by potassium and certain combinations of potassium, magnesium, and calcium

Field experiments in which applications of potash were made to large-seeded type peanuts were initiated on soils of widely different chemical characteristics. A study was made of the effects of potassium when placed in either or both of two zones of plant development (rooting and fruiting zones) with and without calcium or magnesium. Through the use of a rather detailed system of fruit classification, it was found that potassium did not aid in the filling of fruit and that under certain conditions it lowered the true shelling percentage and percentage of ovarian cavities filled. For example, when compared with no treatment, potassium placed in the rooting medium tended to inhibit kernel development whenever the fruiting medium received potassium or was left untreated. When potassium was used in the fruiting medium, it lowered both quality and yield whenever the accompanying rooting medium treatment supplied either potassium or magnesium. The effect of potassium in the fruiting medium was less pronounced whenever the rooting medium received calcium or was left untreated. When potassium was applied to the fruiting zone and used in combination with calcium applied in the same area, it had no unfavorable effect on quality. The necessity of meeting the calcium requirement of the peanut fruit before the true effects of added potash on yield can be measured was emphasized. Even when the calcium supply was adequate for normal fruit development, however, yields were not increased by the use of potassium on soils which would ordinarily be considered low in this element for most other crops. On soils of extremely low potash level, however, the use of potash brought about a marked vegetative response and a significant increase in yield. Thus, it is concluded that increased yields from the use of potash may be expected when (a) there is an adequate supply of calcium to bring about good filling of fruit, and (b) when the level of soil potassium is extremely low. Data are presented to show that potassium affects yield through its influence on plant size rather than on kernel development. In general, the use of magnesium had an unfavorable effect upon kernel development particularly when placed in the rooting zone in combination with potassium supplied to the fruiting medium. The favorable effect of calcium upon fruit development was not affected by the addition of potassium or magnesium to the rooting medium. The percentage of oil in plump kernels of the large and medium size was not affected by the potassium, magnesium, or calcium treatments. Although the oil content of the slightly wrinkled kernels in this size group was highest in those from plots which had received added calcium, the difference was small. The direct effects of these mineral elements upon the oil composition of well-developed kernels was of little consequence.