The effect of phosphorus and potassium fertilizers on the growth and yield of yellow grams (Vigna radiata L.)

Abstract

Yellow gram is a cheap source of protein often grown by small scale farmers in Kenya; it is well adapted to even in areas that receive less optimal rainfall and matures in less than 120 days. Yellow gram crop is widely grown and a cheap source of protein for inhabitants in Kisii region; its productivity continues to decline despite the continued use of nitrogenous and phosphate fertilizers. Previous research done has shown that yellow grams do not respond well to nitrogen and phosphorus unless the soils are deficient in these nutrients. Consequently, the growth and yield of Yellow gram depends on fertilizer requirements among other factors such as climate and agronomic practices. This research was done to determine optimal levels of potassium and phosphorus inorganic fertilizers application to realize maximum yields of yellow gram production in the region. A Randomized complete block design (RCBD) experiment consisting of three replicates was carried out in Magwagwa area of Kisii County between September to December, 2018. This experiment was carried out on red volcanic soils having 0.12% N, 15 ppm P205 and 56 ppm K2O. The treatments were: three levels of potassium fertilizer (K0: No potassium (control); K1:20 kg K/ha; and K2:30 kg K/ha) and the second factor was three levels of phosphorus (P0: No phosphorus (control); P1: 20 kg P/ha; and P2: 30 kg P/ha). The effect(s) of the treatment combinations on stem height (in cm), branch number per plant, pod number per plant, pod length (in cm), number of seeds per pod, 100-seed weight, and grain yield per hectare were evaluated. The data collected was subjected to Analysis of Variance (ANOVA) using SPSS 21.0 tool to determine the effect of different treatments. Significant differences in results of the treatments were separated using the Least Square Differences (LSD). Results revealed that different levels of K and P fertilizer application significantly (p<0.05) influenced the growth and yield of Yellow grams. The maximum plant height (94.8 cm), branch number (12/plant), number of pods (98/plant), seed number (10 seeds/pod), length of pod (10 cm), 100-seed weight (29.78 g) and grain yield (4414 kg/ha) were recorded from plots that received 30 kg/ha K2O and 30 kg/ha P2O5, while the control recorded the lowest results. The 30 kg P2O5/ha and 30 kg K2O/ha fertilizer levels enhance yields immensely and were directly proportional to branch density, pod formation and pod length.