INFLUENCE OF PHOSPHORUS FERTILIZER ON POTATO (Solanum tuberosum L.) SEED PRODUCTION IN ACID SOILS IN KENYA

Abstract

One of the major challenges facing potato (Solanum tuberosum L.) production in Kenya is the inadequate supply of high-quality seed. Of the approximated 70,000 tonnes of Kenya’s potato seed annual requirement, only 1 % is available locally. Otherwise, farmers use low quality farm saved seed (KEPHIS, 2016). A major contributor to this state is low and declining soil fertility, particulary phosphorus among other challenges. Unfortunately, there is no documented phosphorus fertilizer rate recommendation for potato seed production in Kenya. This hinders economic utilization of phosphorus fertilizers in achieving optimal production of quality potato seed in Kenya where its deficiencies is dominant. Therefore, this study investigated the influence of different rates of phosphorus fertilizer on potato seed quantity and quality in three test sites: Lari, Ainabkoi and Saboti sub counties. Unica and Shangi varieties were tested. The experimental design was a split plot arrangement in RCBD with three replicates. Absolute control, 0, 30, 60, 90 and 120 kg ha-1 phosphorus were tested. Data collected included tuber weight, tuber quantity, tuber grade, number of eyes tuber-1, tuber specific gravity, final germination percentage and phosphorus use efficiency (PUE). To monitor soil nutrient dynamics, soil pH, soil available phosphorus, total nitrogen and total carbon were determined at planting while soil available phosphorus and phosphorus content in the tubers were determined at harvesting. Data was analysed using analysis of variance (ANOVA) at 5 % confidence levels with GENSTAT software 14th Edition. Means were separated by using error bars with 5 % value. Results indicated that rate of phosphorus application significantly influenced overall potato seed tuber yield in the test sites. At Saboti planting in absolute control and 0 kg ha-1 phosphorus for Shangi and Unica resulted in highest overall seed tuber yield of 33.7 and 33.3 t ha-1, respectively. For Ainabkoi application of 60 and 30 kg ha-1 phosphorus produced highest overall potato seed tuber yields of 20.0 t ha-1 and 18.9 t ha-1 of Shangi and Unica, respectively. For Lari, application of 60 kg ha-1 and 90 kg ha-1phosphorus produced highest overall potato seed tuber yield of 19.0 t ha-1 and 10.4 t ha-1 for Shangi and Unica, respectively. Unica had better final percentage germination than Shangi. In the test sites highest phosphorus use efficiencies at Saboti, Ainabkoi and Lari attained were 0 kg-1 kg-1, 70 kg-1kg-1 and 76 kg-1 kg-1, respectively. During the season, there was a build-up of soil available phosphorus (Bray 2 phosphorus): 57.71 ppm to 65.0 ppm (Saboti); 43 ppm to 52.3 ppm (Ainabkoi) and 20.4 ppm to 29.2 ppm (Lari). Hence, there is need for farmers to test their soils at the beginning of every potato growing season.