Modeling of irrigated wheat yield potential and gap in Iran

Wheat has an important role in feeding the people of world and Iran as well. It provides around 40 percent of edible energy and protein for people in Iran. Closing yield gap can increase wheat production, significantly. The first step of closing yield gap is to quantify the yield gap at a given region or country. The amount of wheat yield gap hasn’t been measured for whole Iran by a global standard protocol so far. The aim of this study is to estimate irrigated wheat yield gap for Iran based on the global yield gap analysis (GYGA) protocol.

GYGA protocol suggested a method to calculate yield gap on a large scale like a country. Based on this protocol, at first the area covered by each weather stations were specified. Second, the main weather stations where cover irrigated wheat lands were selected named reference weather stations (RWS). Third, irrigated wheat potential yield was estimated by SSM-iCrop2-wheat simulation crop model within the RWSs. The actual irrigated wheat yield was calculated for each RWS based on GYGA protocol as well. Forth, amount of the actual and potential yield was calculated for whole country by using the values calculated for the RWS according to GYGA protocol. Finally, the yield gap was calculated by difference between potential and actual yield for the country.

The results of this study showed that average irrigated wheat in Iran was 3.4 ton/ha, average potential yield was 8.8 ton/ha and average yield gap was 5.4 ton/ha (62%). At the moment, irrigated wheat producers just use 38 present of the existing wheat cultivars and environment potential. There was no significant relationship between climate in the irrigated wheat production RWS and irrigated wheat yield gap (based on percent) in Iran and the yield gap was around 62 percent in all the RWSs. If farmers could reach 80% of potential yield of their locations, by improving agronomy practices, average irrigated wheat would reach 7 tons/ha and there is around 2.2 million ha irrigated wheat area in Iran. Thus, average wheat production in irrigated condition would increase from 7.5 million tons to 19.8 million tons.

Owing to existing wheat cultivars and climates in the main irrigated wheat production RWS in Iran, there is a big yield gap of wheat in Iran. The low actual irrigated wheat yield in Iran (3.4 tone/ha) can be attributed to the poor management condition because the existing cultivars and climates have no limitation to reach the yield around 8.8 tone/ha. There are many factors to reduce the yield such as poor seedbed preparation, late planting date, weeds, pests and diseases, nutrition’s deficits, fertilizer amount and timing, irrigation amount and timing etc. If we want to close the yield gap, we have to identify the reasons of yield gap in a given region.