Pea (Pisum sativum L.) is increasingly being rotated with wheat (Triticum aestivum L.) in Montana. Our objective was to compare economic net returns among wheat-only and pea-wheat systems during an established 4-yr crop rotation. e experimental design included three wheat-only (tilled fallow-wheat, no-till fallow-wheat, no-till continuous wheat) and three no-till peawheat (pea-wheat, pea brown manure-wheat, and pea forage-wheat) systems as main plots, and high and low available N rates as subplots. Net returns were calculated as the di erence between market revenues and operation and input costs associated with machinery, seed and seed treatment, fertilizer, and pesticides. Gross returns for wheat were adjusted to re ect grain protein at " at" and "sharp" discount/premium schedules based on historical Montana elevator schedules. Cumulative net returns were calculated for four scenarios including high and low available N rates and at and sharp protein discount/premium schedules. Pea-wheat consistently had the greatest net returns among the six systems studied. Pea fallow-wheat systems exhibited greater economic stability across scenarios but had greater 4-yr returns (US$287 ha -1 ) than fallow-wheat systems only under the low N rate and sharp protein discount schedule scenario. We concluded that pea-wheat systems can reduce net return uncertainties relative to wheat-only systems under contrasting N fertility regimes, and variable wheat protein discount schedules in southwestern Montana. is implies that pea-wheat rotations, which protected wheat yield and/or protein levels under varying N fertility management, can reduce farmers' exposure to annual economic variability.

M ultispecies cover crop mixtures are quickly gaining popularity in the United States. According to a national survey of cover crop users, adoption of multispecies mixtures increased 38% between 2012 and 2016 (CTIC and SARE, 2013; CTIC, 2017). Compared with traditional monoand biculture cover crops, mixtures have the potential to optimize across a wider range of ecosystem services, such as building soil organic matter, reducing N leaching, and improving yield of the following crop (Creamer et al., 1997; LaChance et al., 2015; Finney and Kaye, 2016). However, there is little published evidence of the effects of cover crop mixtures on subsequent crop yields, especially for multiple crops grown in rotation (Welch et al., 2016; Chu et al., 2017). A recent meta-analysis (Marcillo and Miguez, 2017) found that maize (Zea mays L.) yield increased an average of 13% following cover crop mixtures compared with no cover crop, but these were predominantly bicultures. Most studies of multispecies cover crops have found little or no effect on the yield of the following cash crop (Smith et al., 2014; Welch et al., 2016; Appelgate et al., 2017), except when cover crops affected soil water availability (positively or negatively) in semiarid environments (Wortman et al., 2012; Reese et al., 2014; Nielsen et al., 2016). However, Chu et al. (2017) showed that soybean [Glycine max (L.) Merr.] yield was higher following 3 yr of a diverse cover crop mix, potentially due to increased soil moisture content. A small body of literature indicates that cover crop mixtures can strongly influence the yield of the following crop by affecting soil N availability, particularly for crops with high N demand, such as maize (

Annual legume green manure (LGM) cover crops may have potential in dryland wheat (Triticum aestivum L.) production areas where rotation with whole-year summer fallow is practiced. No-till cropland management enhances soil water conservation, possibly enabling cover cropping, but tillage may be necessary to stimulate mineralization of LGM N in time to affect crop yield. A 2-yr LGM-wheat crop sequence study was repeated three times in Montana, with mean annual precipitation of 356 mm. Spring-planted pea (Pisum sativum L.) and lentil (Lens culinaris Medik.) The LGM were terminated at first bloom with tillage or herbicide. Post-termination weed control also was accomplished with either tillage or herbicide in a factorial combination with the termination treatments, resulting in four management regimes. Fallow and non-N-fixing cover crop controls were included and subjected to the same management regimes. Spring wheat was grown the following year in subplots with four levels of N fertilizer. Wheat tiller density increased only when LGM was tilled at least once. Tillage also resulted in reduced soil water storage and wheat kernel weight in 1 yr. Effects on grain yield were usually neutral or positive, with pea more frequently having a positive effect than lentil, and interactions with tillage varying each year. Wheat grain protein was increased by pea LGM regardless of tillage, even when LGM did not affect wheat yield, indicating that LGM N supply is accelerated by tillage. Managing LGM in dryland environments involves a tradeoff of soil water for N supply, and tillage affects this balance.

Crop-fallow systems dominate many semi-arid agricultural regions despite fallow's negative effects on soil and water quality. Annual legumes grown as a fallow-replacement crop, and terminated prior to maturity, can reduce these negative effects without substantially decreasing plant available water for the subsequent crop. Interest in growing legume green manures (LGMs) in synthetically-fertilized systems is increasing in the northern Great Plains of North America, partly due to the N-fixing capabilities of legumes; however, little is known about the effects of planting and termination time on N fixation amounts in the region. A 2-year field study was initiated in southwest Montana to determine the effects of planting time (spring or summer) and termination time (e.g. flower or pod) on the amount of N fixed by field pea (Pisum sativum cv. Arvika) and lentil (Lens culinaris cv. Richlea). Two methods, 15 N natural abundance and N difference, were used to quantify N fixation, with wheat or in-crop weeds as reference plants. In 2009, N fixed by spring-planted lentil was higher by pod than flower (P = 0.03). Termination time did not affect the amount of N fixed by spring-planted pea, despite more biomass by pod than flower. In 2010, both spring-planted crops fixed more N by pod than flower (P \ 0.01) and more N was fixed by spring-planted than summer-planted crops (P \ 0.01). These results should prove useful to growers interested in selecting management practices that optimize N fixation of LGMs.

The rotational effects and economic potential of incorporating fall‐seeded pea (Pisum sativum L.) and lentil (Lens culinaris Medik) into conventional wheat (Triticum aestivum L.)‐based cropping systems in the northern Great Plains are not well understood. Two 2‐yr crop rotation experiments were conducted in central Montana to investigate how winter pea hay, lentil green manure, and lentil grain affects subsequent winter wheat yield and protein content, as well as the economic returns of the systems under no‐till conditions. In Exp. 1, a winter pea hay–winter wheat (WP–WW) rotation was compared to fallow–winter wheat (FW–WW) and spring wheat–winter wheat (SW–WW) rotations. In Exp. 2, a winter lentil for green manure–winter wheat [WL(m)–WW] rotation was compared to a winter lentil grain–winter wheat [WL(g)–WW] rotation. Four different rates of N were applied to the winter and spring wheat. Winter wheat yield in the WP–WW rotation was 2193 kg ha−1, which was equivalent to the yield in the FW–WW rotation (2136 kg ha−1), and much greater than the SW–WW rotation (1155 kg ha−1). Averaged over all N rates, the WP–WW, FW–WW, and SW–WW systems had $196, $116, and $41 ha−1 net return, respectively. In Exp. 2, the WL(m)–WW rotation produced greater grain yield and protein content at lower N input levels, indicating a greater N benefit. Nevertheless, the WL(g)–WW system generated $213 ha−1 net profit while the WL(m)–WW system produced $92 ha−1. Therefore, the winter pea cover crop, used for livestock feed, improves the system profitability.