Читать книгу Dry Beans and Pulses Production, Processing, and Nutrition - Группа авторов - Страница 34

Dry beans are a short season crop that matures in 85–100 days. Consequently, beans are produced largely in northern states or at higher elevations in the intermountain and western states. Approximately 70% acreage planted to beans in the US is grown under rainfed conditions in the East, Midwest, and Upper Midwest, whereas essentially all western production in semiarid states is grown under irrigation. Yields reflect the availability of water resources and the highest yields are produced in irrigated regions. The major production areas and seed types grown in these states are shown in Figure 2.1. Beans are grown as a row crop in all states, and row widths vary by location, irrigation systems, and harvest methods. In recent years, growers in the Midwest have moved from wider 70–75 cm to narrower 35–55 cm row spacings as newer varieties are more upright, thus better suited for direct harvest. To optimize productivity and better utilize water in western states, growers tend to plant higher plant population densities in 55 cm row spacing. Few producers drill beans (18–25 cm rows), because it often results in shorter, more difficult‐to‐harvest plants and inconsistent yield advantages.

US planting time depends on the speed of warm up in the spring and the length of growing season. Beans require soil temperatures of 13 ^°C at 5 cm depths to ensure favorable germination and growth. Dates can vary from mid‐May in the Pacific Northwest and Upper Midwest to mid‐June in the East and Midwest to early July in California, which has a longer growing season. Seeding rates vary by seed types; small‐seeded navy and black beans at 40–60kg/ha; medium‐seeded pintos, red beans at 50–65 kg/ha; and larger‐seeded kidney and cranberry beans at 75–90 kg/ha.

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.