Inoculant and fertilizer effects on lentil in the US northern Great Plains

Lentil (Lens culinaris Medikus) is an important crop, averaging over 250,000 ha in Montana and North Dakota during 2016-2021. However, relatively little is known about rhizobial inoculant and fertility response in lentil in the US northern Great Plains. The objective was to evaluate the effect of rhizobial inoculant formulations (seed coat and in-furrow) and nutrient additions (potassium [K], sulfur [S], and micronutrients) on lentil yield and seed protein concentration. This study was conducted at seven university research centers in Montana and North Dakota from 2019 to 2021, resulting in 20 location-years of data. In six of 20 experiments, inoculant application increased seed yield by an average of 36% (323 kg ha-1, p <= 0.05) but had no consistent effect on seed protein concentration. Lentil or pea crop history among locations did not explain inoculant response. Inoculant formulations (seed coat vs. in-furrow) and K fertilizer had inconsistent and small effects on seed yield and protein concentration. However, S fertilizer (5.6 kg S ha-1) increased seed yield in four of 20 experiments (p <= 0.02) by an average of 14.5% (255 kg ha-1) in those experiments and decreased seed yield for one experiment (p = 0.05) by 5.8% (153 kg ha-1). Pre-plant SO4-S soil test levels did not predict lentil response to S fertilizer. Micronutrient application was assessed in 12 location-years but had no effect on lentil yield or protein concentration. This research suggests a need to better understand what factors control lentil yield and protein response to rhizobial inoculant and S fertilization. Rhizobial inoculant increased seed yield in 30% of experiments regardless of prior lentil or pea crop history. Sulfur fertilizer increased seed yield and protein concentration in 20% of experiments. There was little to no relationship between pre-plant SO4-S soil test levels and S fertilizer response.