Estimation of Potato (Solanum tuberosum L.) Yield Gap and Determining the Contribution of Water and Nitrogen Across Khorasan Razavi Province using Modeling Approach

IntroductionThe growing human population, global warming, depletion of water and soil resources, and climate change make it imperative to reconsider food production methods in agricultural systems. Improving resource use efficiency and enhancing productivity are key strategies to address these challenges. Reducing the gap between the actual yield currently achieved on farms and the yield that could be achieved using the best environmentally compatible cultivars and the best water, soil and plant management practices is a key solution to overcome the challenge of feeding the world's growing population. The first step in addressing the yield gap is to determine how much and how it is distributed.Materials and MethodsTo estimate the potato (Solanum tuberosum L.) yield gap in Khorasan Razavi province and to determine the contribution of water and nitrogen to it, two separate field experiments were conducted based on randomized complete block design (RCBD) with water and nitrogen limitation conditions for potato cultivars in the city of Quchan during the growing season of 2018-2019. The first experiment was conducted with three irrigation levels of 100, 75, and 50% water requirement, and used two potato cultivars. The second experiment was conducted with four levels of nitrogen, including 0, 50, 100, and 150 kg of pure nitrogen, and also included two potato cultivars.Results and DiscussionThe results showed that increasing nitrogen fertilizer application improved many of the evaluated characteristics of two potato varieties. However, with the increase in nitrogen use, nitrogen use efficiency (productivity) decreased. The potential yield of potatoes in different regions of Khorasan Razavi province was estimated using the DSSAT model. The data obtained from one of the field experiments, including dry matter, leaf area, phenology (developmental stages), and yield, were used to calibrate the model. After determining the potential yield and estimating the yield gap, the contribution of water and nitrogen to the yield gap was identified. Based on the protocol provided by the Global Yield Gap Atlas, the province was clustered into three regions. Region 1 (R1) includes the cities of Quchan and Fariman; Region 2 (R2) comprises Golmakan, Neyshabour, Torbat-e Hydarie, Mashhad, and Dargaz, which lie between regions 1 and 3; and Region 3 (R3) includes the cities of Torbat-e Jam, Gonabad, Khaf, Kashmar, Sabzevar, Sarakhs, and Bardaskan. The model was calibrated and validated with the data obtained from the field experiment. Long-term weather data and average actual yield were collected for each station, and the potential yield in each station was simulated using the model. Then, the difference between the potential yield and the actual yield was calculated, and the yield gap was determined for each area. Afterward, using the model, the potential yield was recalculated under water and nitrogen limitation conditions, and the contribution of water and nitrogen to the yield gap was assessed.ConclusionIn R1, the yield gap varied between 40.5 and 57.7 ton ha-1. The average yield gap during 10 years was estimated at 48.8 and 31.7 ton ha-1 for R1 and R2, respectively. According to the DSSAT model's results, R3 had a lower potential yield than the other two regions. The average contribution of water and nitrogen limitations to the potato yield gap in R1 and R2 was calculated. Accordingly, in R1, the impact of water and nitrogen limitations was 12.1 and 18 ton ha-1, and in R2, it was 10.9 and 8.3 ton ha-1, respectively. Although narrowing the yield gap depends on the climatic conditions of each region, selecting a compatible crop variety, optimizing planting date, and adopting appropriate plant density are among the most effective crop management strategies to reduce the yield gap, regardless of climatic differences.