Effects of nitrogen and irrigation regimes on performance of potato (solanum tuberosum l.) Grown in a mollic andosol

Abstract

Nitrogen (N) deficiency in soils and reduced seasonal rainfall contribute to low potato (Solanum tuberosum L.) yield in Kenya. Nitrogen deficiency is the major problem faced by the smallholder potato farmers of Kenya due to lack of fallows and knowledge in its management. The objective of this study was to determine the effects of nitrogen and irrigation regimes on the performance of potato grown in a mollic Andosol. Field and rain shelter experiments were conducted for two growing seasons in the research fields of Egerton University, Njoro, Kenya. A randomized complete block design in a split-plot arrangement was used for both experiments. The main plot treatments for the field experiment comprised full supplemental irrigation (FI) and rain-fed potato production (RF). For the rain shelter, the main plot treatments were100%, 85%, 75% and 50% of the crop evapotranspiration (ETC), where ETC100% was irrigated according to the soil water depletion 2 days after full irrigation. In both experiments, the subplot treatments were 0 (N0), 60 (N1), 90 (N2) and 130 kg N ha−1 (N3) rates. For the field experiment, the results showed the highest tuber yield, 62.12 tonnes per hectare (t ha−1), under FI combined with N3. FI increased marketable yield by about 125.58% in all N treatments compared to RF. The optimum nitrogen use efficiency (NUE), 224.23 kg kg−1 N, was obtained under FI with N3. Application of 130 kg N ha−1 produced the highest water use efficiency (WUE) of 14.24 kg m−3. For the rain shelter experiment, potato crop water demand was on average 201.4, 302.1, 342.4 and 402.8 mm under ETC50%, ETC75%, ETC85% and ETC100%, respectively. Potato grown under ETC100% with N3 produced the highest total tuber yield, 58.28 t ha−1, and marketable yield, 54. 21 t ha−1. The highest tuber dry matter, 30%, was obtained with 130 kg N ha−1, while the maximum harvest index (HI), 57.12%, and WUE, 17.5 kg m−3, were obtained under ETC50% with 130 kg N ha−1. Treatment ETC100% with 90 kg N ha−1 resulted in the highest NUE, 208.30 kg kg−1 N. The correlation coefficients for % N leaf and leaf chlorophyll, and % N leaf and normalized difference vegetation index (NDVI), were highest at 88 (r = 0.59***) and 67 days after planting (DAP) (r = 0.57***), respectively. A high potato yield in a mollic Andosol can be achieved in Nakuru by introducing FI with an application of 130 kg N ha−1. If maximizing NUE in a mollic Andosol is the purpose of the farmers, then it should be at the expense of potato NUE. Leaf chlorophyll and NDVI can be used for in-season N management at the early growth stages of potato, but the effects of water stress and growth stages of the crop should be taken into account for an accurate N assessment.