Response of Potato to Drip and Gun Irrigation system

The objective of this study was to evaluate effects of different irrigation and N fertilization regimes by gun irrigation and drip-fertigation on potato production, and subsequently optimize the supply of water and N fertilizer to the growth condition of the specific season and minimize nitrate leaching without compromising profits. Four replicate plots of each treatment with varying predefined and model-based (Daisy and Aquacrop crop model) irrigation and N fertilization levels was used in the study. Two experiments were conducted. In experiment-I, treatments consisted of one drip-fertigation system (IdsNds) and two gun irrigation systems (GIdsN120 and GIaN120) to display the differences on growth, yield and water use efficiency of potato. All treatments were irrigated according to model simulated soil water content. For fertilization all treatments received a basic dressing at planting of P, K, Mg and micronutrients, and in addition 120 kg N/ha in the gun irrigated treatments and 36 kg N/ha in the drip-fertigated. For the latter, portion of 20 kg N/ha was applied whenever plant N concentration approached a critical value as simulated by the Daisy model. As a result differences in soil water deficit and nitrogen application rates emerged during the season. Soil water content in the drip-fertigation system was higher than gun irrigation systems most time during growth season, with less N used in total (100 kg N/ha) in IdsNds. GIaN120 used 20 mm less water than the GIdsN120 treatment. Yield was not significantly different between treatments. As a consequence GIaN120 had higher irrigation water use efficiency than IdsN120 and IdsNds: 23 and 18 %, respectively In experiment-II, 14 treatments with different combinations of irrigation and N levels was conducted, all using the fertigation system, among which several treatments were irrigated and/or fertilized with assistance of the Daisy model. Results showed that, soil water content was well simulated by the Daisy model (low root mean square error (RMSE)), whereas the Aquacrop model had higher RMSE, suggesting a requirement of calibration to entail a better performance of Aquacrop model. Increasing N supply showed expected  effect on fresh yield, treatments applied with 60, 100, 140 and 180kgN/ha increased fresh yield by 77, 83, 90 and 106 % compared to treatment without N application. N-fertigation based on Daisy (I1Nds) got higher fresh yield than I1N2, I1Norg and I1Nt by 2, 4 and 14 %, respectively, even all received 100kg N/ha. Hence some effect of N fertilization timing was found, i.e. varying time of the last fertigation. The results indicated giving N too early or late may result in decline of fresh yield. In contrast, increasing irrigation in 140 kg N/ha treatments decreased yield by 4 %. In addition, treatments guided with Daisy or Aquacrop had higher irrigation water use efficiency, suggesting that the use of models to guide application allowed a better use of water and N fertilizer in potato production