Dry Beans and Pulses Production, Processing, and Nutrition. Группа авторов

Fig. 2.1. Bean production states comparison based on harvested acreage in 2020 and most common seed types grown.

      Source: USDA‐NASS (2020a).

      Most growers use a starter fertilizer (50 kg N/ha) based on soil type and analysis. Pre‐ and post‐emergence applied herbicides are widely used to control weeds as fewer farmers cultivate the crop so as not to disturb the soil surface for purposes of furrow irrigation in the western states or for direct harvest in the Midwest. In recent years, growers in Michigan have taken to rolling fields after planting to ensure a flat surface suitable for direct harvest and to bury stones to reduce damage to harvest equipment. Depending on production region, insecticides are applied at recommended rates to control an array of insect pests, including potato leaf hoppers, spider mites, thrips, bean beetles, western bean cutworms, and tarnished plant bugs that may appear in that region. Seed treatments with a mix of insecticide and fungicides, and often a bactericide, are used to control early season insect pests and diseases. Foliar fungicides are applied largely to control Sclerotinia white mold in more humid regions of the Midwest and Upper Midwest. For direct harvested beans, harvest‐aid chemicals are often used to ensure uniform dry‐down and desiccate weeds (Gaultier and Gulden 2016).

Two contrasting methods are used to harvest beans, depending on plant type and seed size, location, local weather conditions, and irrigation systems. The traditional harvest method widely used throughout the US is to mechanically undercut (pull) beans into windrows of 6–12 rows and then thresh windrows when plants are dry using a pickup header on commercial combines. In the western states, to avoid large seed losses from pod shattering due to low humidity conditions, beans are pulled at physiological maturity when they are still green and left to ripen in the windrow for 7–10 days before being threshed. In the Midwest, where erratic rains are problematic, growers cut/pull and windrow mature plants early in the morning (4:00–11:00 a.m.) when dew adheres to the plant, thus preventing pod shattering, and the windrowed plants are threshed the same afternoon. Prostrate vine‐type varieties or those severely lodged are particularly suited to the traditional pulling system, as they would suffer major seed loss if direct harvested. In those areas where furrow irrigation is used and the soil surface is uneven, the ridged rows facilitate knife‐pulling, as do hilled rows for weed control. Conversely, rod‐pullers have the action of grabbing and pulling the plants out of the ground rather than cutting them. Bean roots are still attached to the plant following both pulling operations and enter the combine at threshing. This extra plant mass has a cushioning effect during threshing, which is particularly advantageous for larger‐seeded kidney beans, which are easily damaged at harvest.

      With the development of upright lodging‐resistant varieties, an increasing number of growers are direct harvesting the bean crop, which saves time, fuel, labor, and equipment. In Michigan approximately 90% of the dry bean crop is direct harvested. But only small‐seeded and a few medium‐seeded varieties can be direct harvested as larger‐seeded types are better suited to traditional harvest methods. Following harvest, beans are transported in bulk to local elevators where the crop is cleaned, stored, graded, sold, and shipped into national and international markets. Since bean varieties from the same commercial class are often comingled at the elevator, all commercial varieties need to meet similar quality standards for seed size, shape, color, and canning quality. Although the largest production areas are located east of the continental divide, the majority of bean seed for planting is produced in the semiarid states of Idaho, Washington, and California. The occurrence of endemic seed‐borne diseases such as common bacterial blight and anthracnose limits seed production in the Midwest as plants may become infected, preventing their sale as seed. The absence of these pathogens and strict quarantine in states such as Idaho ensures that disease‐free seed can be produced. Higher yields in these irrigated production areas help offset transportation and irrigation costs of western‐produced seed. Commercial growers in the Midwest generally prefer western‐grown seed, as it has the assurance of being disease free. Some growers are willing to pay the higher price for western seed by spreading the cost over more than one growing season as they will plant bin‐run seed the second season, assuming no disease problems arise.

Production trends

Dry bean yields from the onset of early breeding efforts in the early 1900s to now have seen just less than 1% yield gain per year, a value commonly reported for soybean (Figure 2.2). In most crops, yield gains are attributed equally to changes in genetics and management and a similar combination of management and genetic factors contributed to bean yields. Periods of increasing yield gains and lulls have occurred along the way. A plateau with 1500 kg/ha average yields occurred from 1960–1979, followed by a modest upward trend to 1900 kg/ha in 2000. Since 2000, yields have oscillated around 1900 kg/ha even though higher yielding varieties have been released (Vandemark et al. 2014). The movement of production from highly productive hectares grown under irrigation in the western US (a 50% decline) to less productive regions in North Dakota the last 20 years, has likely contributed to the recent lull in yields and a perceived lack of genetic yield gains.

A major wake‐up call for bean breeders in the US came in the 1972 report on genetic vulnerability of crops published by the National Academy of Sciences (NRC 1972) that emphasized the need for greater genetic diversity to combat genetic vulnerability. Prior to the 1980s, the seven bean‐breeding programs across the US were small, isolated efforts (Table 2.1). These programs focused largely on local needs in a range of diverse seed types that resulted in limited exchange and use of bean germplasm from other programs. Many programs expanded breeding and testing programs in that era, as the need to change the status quo was obvious. The positive genetic changes resulted from the use of wider crosses that exploited greater genetic diversity and improved germplasm from other programs. The International Center – CIAT, established in the late 1960s in Cali Colombia was an important new source of wider genetic diversity of improved germplasm during this time. In 1973, CIAT sponsored a conference on ways to enhance the “Potential of field beans and other legumes in Latin America.” The approach of using “Plant architecture and physiological efficiency in the field bean” (Adams 1973) to enhance yields opened the door to new breeding approaches, and the development of new architectural types with broader adaptation and higher yield potential (Adams 1982; Kelly 2000). The liberal use and exchange of materials between CIAT and US breeding programs revitalized many of these programs. In addition, funding from Rockefeller Foundation in the mid‐1970s also encouraged the utilization of new germplasm, which led eventually to the establishment of USAID funding of the Bean/Cowpea Collaborative Research Support Program (B/C CRSP) project in 1980 (Adams 2003). The B/C CRSP and recent iterations, the Feed the Future (FtF) Pulse CRSP; Legume Systems Innovation Lab (FtF 2021a); and USDA‐ARS Bean Research Team (FtF 2021b) projects have not only encouraged better longstanding integration among breeding programs in the US, but among many institutions in the Caribbean, Latin America, and Eastern and Southern Africa, where the common currency was germplasm exchange and utilization. For example, landrace bean germplasm from Malawi was introduced for testing in Michigan (Martin and Adams 1987) and added to the National Plant Germplasm collection. A summary of the new varieties developed through these different CRSP programs in a number of countries including the US was published by Beaver et al. (2003, 2020).

Fig. 2.2. Dry Bean yields (kg/ha) in the US over 110 years since 1909.

      Source: Updated from Vandemark et al. (2014) using USDA‐NASS (2020b) data.