tony.fischer@anu.edu.au

The farm yield (FY) of irrigated wheat in the Yaqui Valley of NW Mexico has risen from 2 to 7 t/ha from 1960 to 2019, due to efforts of CIMMYT, and Mexican researchers and farmers. This progress has been and remains influential for yield progress involving disease resistant wheat globally below around latitude 35o.

Fischer et al (2022) divided this Yaqui Valley period into three consecutive 20 year subperiods for detailed study. FY was corrected for annual FY fluctuations related to such fluctuations in minimum temperature (Tmin, yield response -7%/oC), and the small upwards 60 yr trends in Tmin and CO2, to get accurate linear technology trends. For each consecutive 20-y period, this was 4.2, 0.5, and 1.6 % p.a.

Knowing the relative area and potential yield (PY) of varieties grown each year allowed calculation of a variety yield index for the Valley, which increased by 1.0, 0.5, and 0.7% p.a. over the successive 20 year periods. By difference, agronomic + socioeconomic factors therefore contributed 3.2, 0, and 0.9% p.a., respectively. The large 1960-79 figure was boosted by the only N x variety interaction, large and positive.

Agronomic progress itself was largely due to steadily higher N and P fertilizer rates, better weed control, and improved planting and water management (raised bed system); in the final period there was probably also more skillful agronomic management. However, over the 60 years cropping system diversity has declined.

The depressed agronomy+ progress in 1980 to 1999 was largely due to the withdrawal of Government support to the small-farmer ejido system and to prices. Since 2019, FY corrected for temperature has not increased, nor has the variety yield index, with progress in breeders’ plots no better than 0.5% of current PY. Have we reached the limit?

Fischer, T., Ammar, K., Ortiz Monasterio, I., Monjardino, M., Singh, R., Verhulst, N. 2022 Sixty years of irrigated wheat yield increase in the Yaqui Valley of Mexico: past drivers, prospects and sustainability. Field Crops Research 283, 108528.