A Comparison of Pigeonpea and Cowpea Forage Yield and Nutritive Value in the Southern High Plains of the USA
Pigeonpea [Cajanus cajan
cowpea [Vigna unguiculata]currently the most commonly used warm-season annual legume in the region
Cowpea was superior to pigeonpea for forage yield in 2006 and had numerically higher yield in 2007 [6.39 vs. 3.59 Mg ha-1 for cowpea and pigeonpea, respectively, in 2006 (P <0.01) and 5.07 vs. 4.06 Mg ha-1 in 2007 (P <0.30)].
Forage nutritive value of cowpea was greater than pigeonpea in both years as estimated by crude protein [189 vs. 156 g kg-1 in 2006 (P <0.05) and 130 vs. 88 g kg-1 in 2007 (P <0.01)]
Based on these results, cowpea remains the better option than pigeonpea for forage production systems under irrigation in the Southern High Plains of the USA and similar higher elevation, semiarid, subtropical environments.
Forage sorghum [Sorghum bicolor(L.) Moench] and sorghum x sudangrass (S. bicolorvar. Sudanese) are important warm-season annual forage grasses in the higher elevations of the semiarid, subtropi-cal Southern High Plains of the USA (eastern New Mexico and Texas Panhandle) because they are rela-tively drought-tolerant and productive. However, there are limitations regarding crude protein (CP) concentration and other nutritive value compo-nents, such as fiber and digestibility, and livestock may require supplementation if these components are too low (Mislevy et al., 2005; Contreras-Govea et al., 2009).
Some of these deficiencies in nutri-tive value can be alleviated by including legumes in the forage system (Muir, 2002; Lauriault and Kirksey, 2004; Contreras-Govea et al., 2009).
Soybean (Glycine maxL.) is widely adapted; however, drought limits its forage yields (Ishibashi et al., 2003; Mislevy et al., 2005), and the combi-nation of high temperature and low humidity in the Southern High Plains increases the irrigation requirement for soybean and reduces grain yield (C. Trostle, personal communication, 2009).
Cowpea [Vigna unguiculata(L.) Walpers] is well adapted to low soil moisture situations (Muir, 2002), but not wet soils (Mislevy et al., 2005). Lauriault and Kirksey (2007) found that black-eyed cowpea grown for edible dry beans was well adapted to the Southern High Plains, with no grain yield reduction if planted before mid-June or if furrow irrigation or precipitation were timely, albeit limited. Data published by Contreras-Govea et al. (2009) indicate that forage cowpea has the potential tosignificantly improve nutritive value of monoculture sorghum forages
Studies were conducted in 2006 and 2007 at the New Mexico State University Agricultural Science Center at Tucumcari, NM (35.20° N, 103.68° W; elev. 1,247 m)
average annual temperature and precipitation for this location are 14.4°C and 404.1 mm, respectively (Kirksey et al., 2003). The precipitation pattern in the area is continental, with approximately 80% (302.1 mm on average) falling from April through September (Kirksey et al., 2003)
Figure 1.Mean monthly air temperatures and total monthly precipitation during 2006 and 2007 and the long-term (1905-2005) averages at Tucumcari, NM, in the semiarid, subtropical Southern High Plains of the USA [pdf 3]
In 2006, the soil was Canez fine sandy loam (fine-loamy, mixed, thermic Ustollic Haplargid pH of 8.4 and N, P, and K levels of 10, 19, and 210 ppm
In 2007, the soil type was Redona fine sandy loam (fine-loamy, mixed, superactive, thermic Ustic Cal-ciargid) The pH of this soil was 7.2 and N, P, and K levels were 1, 2, and 19 ppm,
These data indicate that cowpea forage yield and nutritive value are superior to pigeonpea under ir-rigation in the Southern High Plains of the USA and similar higher elevation, semiarid, subtropical environments. Lower productivity of pigeonpea in this environment compared to other locations described in the literature may have been related to differences in climatic and soil effects [pigeonpea may be superior in the lower southern great plains]