Agro-economic returns were reduced for four years after conversion from perennial forage

Abstract

Perennial crops are increasingly converted to annual cropping systems as Conservation Reserve Program (CRP) contracts expire. We compared crop yields and net returns across 2013–2018 for no-till pulse crop-wheat (Triticum aestivum L.) (P-W) systems, preceded either by 10 yr of P-W or 10 yr of perennial cropping (P-WPer) at Bozeman, MT. The perennial mixed species planting, dominated by alfalfa (Medicago sativa L.), was split into unharvested and annually harvested treatments 2005–2012. The 2013–2018 experimental design included both systems replicated as main plots, with 50 and 100% recommended available N rates as subplots. Precipitation was below average during three of the first four growing seasons, followed by two wetter than average years. The P-WPer system had generally lower soil moisture and equal or greater nitrogen supply than the P-W. ‘Haying off’ (reduced harvest index) occurred in wheat grown 2 and 4 yr after conversion from perennial to annual cropping, which reduced grain yield, and increased grain protein. Crop yield losses in the P-WPer system averaged 0.84 Mg ha–1 (28%) over 4 yr and two N rates. After adjusting grain prices using historical discounts and premiums for test weight and protein content at Montana grain elevators, P-WPer net returns were reduced for four consecutive years in three economic scenarios, and for 2 yr in a fourth scenario by a 4-yr cumulative average of (USD) $731 ha–1 (45%). We conclude annual crop yield and economic returns were compromised for 4 yr following 10 yr of an alfalfa-dominated perennial cropping system.