Agronomic Feasibility of a Continuous Double Crop of Winter Wheat and Soybean Forage in the Southern Great Plains

Abstract

In the southern Great Plains, dryland double‐cropping soybean [Glycine max (L.) Merr.] after winter wheat (Triticum aestivum L.) could provide quality summer forage, partially offset mineral fertilizer N applied to winter wheat, and lessen soil erosion. Waiting for wheat grain to mature, however, delays soybean planting and subjects growth to dry and hot conditions. Planting soybean after a hay crop of wheat was investigated to determine the feasibility of the system as a source of livestock feeds and N uptake by both crops. Twelve treatment combinations of two wheat fertilizer N levels (0 and 112 kg N ha−1) and six summer management treatments (fallow: conventional and no‐till; soybean: grazed, cut for hay, green manure, and mulch) were arranged in strips across four replications. Soybean biomass ranged from 1.35 to 1.90 Mg ha−1 when soybean grazing and harvest occurred at seed fill, and crude protein ranged from 129 to 220 g kg−1 resulting in a 3‐yr average N uptake of 44 kg ha−1 Within each N fertilizer level, average wheat forage yields were not different, but yield increased 29% with N fertilizer and crude protein was inversely related to yield. Double‐cropped soybean failed to offer any yield‐enhancing N benefit to wheat or enhance soil N and C content after 3 yr, even when used as a green manure. Unless a producer is willing to accept the low productivity of soybean as a double crop with wheat, the feasibility of this dryland double‐crop forage system is limited.

Green Manure and Forage Potential of Lablab in the U.S. Southern Plains

“…Soybean digestibility and CP concentration noted in this study was similar to concentrations reported in earlier experiments undertaken at the research site (Rao et al, 2005; MacKown et al, 2007; Rao and Northup, 2009a). Rao et al (2005) reported IVDDM of whole plant biomass for three forage‐type cultivars ranged from 750 and 805 g kg −1 , with 170 to 185 g CP kg −1 .…”

“…One key factor could be a shortage of available N to drive the production systems. Earlier research found soybean biomass used as green manures in wheat rotations of central Oklahoma failed to provide improvements in soil N to support subsequent wheat crops (MacKown et al, 2007). Monitoring at the current study site noted the plots receiving the legume treatments had 1025 mg total N kg −1 soil in 2008 and 1003 mg N kg −1 soil in 2011.…”

The Current Status of Forage Soybean

“…Double-cropping soybean as forage after winter wheat, winter rye, and spring barley was practical in the north central USA environment (LeMahieu & Brinkman 1990). Dry land soybean in a wheat-soybean forage double-crop system in the southern Great Plains in the USA failed to offer any N benefit to the following winter wheat crop, when grazing or harvest of the soybean was initiated soon after growth stage R5 (MacKown et al 2007). Use of a forage-type soybean, and extending the growth period before incorporation as a green manure, could increase soybean biomass and the amount of aboveground N, to benefit the following winter wheat crop (Rao et al 2005).…”

Effects of Polymer‐Coated Urea Application Ratios and Dates on Wheat and Subsequent Double‐Crop Soybean

“…Soybean double cropped with soft red winter wheat is a common practice in the Midwest (Kyei‐Boahen and Zhang, 2006). Double cropping soybean allows producers to generate income and maintain wheat in the crop rotation while reducing the potential for erosion through increased soil cover (MacKown et al, 2007). However, double‐cropped soybean yields have been reported to be 16 to 33% lower than full‐season soybean (Pfeiffer, 2000).…”