Consecutive hard freezes in the winters of 1950-51 and 1951-52, severely damaged white and blue lupin, essentially eliminating lupin seed stocks (Reeves 1991; Burton et al. 1954). Loss of government price supports, low cost nitrogen fertilizer, and disease pressure also contributed to the regional decline of this crop (Reeves 1991; Burton et al. 1954). The recent interest in sustainable agriculture, and the suitability for double-cropping with winter grown lupin, however, have generated renewed interest in winter-hardy white lupin for the South.
Several characteristics of winter-hardy white lupin make it suitable as an alternative crop for the area. The species is adapted to the coarse-textured, relatively infertile, acidic soils which predominate the area. The growing season of winter-grown white lupin is similar to wheat (Triticum aestivum L.) and allows for double-cropping rotations with other crops grown in the area, such as sorghum [Sorghum bicolor (L.) Moench], late-planted tropically adapted maize (Zea mays L.), and soybean [Glycine max (L.) Merr]. Development of cropping systems with lupin as a component would: (1) provide a cover crop when erosion potential is greatest; (2) provide a rotation yield response to subsequent summer grain crops; (3) contribute to reducing or eliminating nitrogen fertilizer requirements of summer grain crops as well as replacing a winter crop requiring nitrogen fertilizer, viz., wheat; and (4) produce quantities of high protein feed grain that could be used on-farm without processing.
The main competitive crop of lupin is winter wheat. However, at current yield levels and prices, wheat is not a profitable crop for the southeastern United States. In Alabama for example, even at yield levels 20% greater than the state average, producers lose approximately $86.45/ha (Novak et al. 1991). The single largest variable production cost for wheat is nitrogen, accounting for approximately 28% of input costs. A reliable white lupin would be economically superior to wheat because it would not require nitrogen. Efficiency of nitrogen for winter wheat in the southeastern United States is low due to generally warm temperatures and excessive rainfall. This results in large nitrogen losses via leaching and denitrification. Therefore, the use of lupin also has great potential for reducing nitrogen losses to the environment, and subsequent ground and surface water contamination.
In 1987-88, a study was initiated comparing 'Tifwhite-78' white lupin, 'Tifblue-78' blue lupin, and 'Bicolor-1' lupin [Lupinus hispanicus ssp. bicolor (Merino)] to common cover crops used in the Southeast, i.e., crimson clover (Trifolium incarnatum L.) and rye (Secale cereale L.). The primary comparison factor was nitrogen contribution to a following crop of maize. The cover crops were planted in mid-October of 1987, 1988, and 1989. Nitrogen was applied to the maize following the cover crops at rates of 0, 56, 112, or 168 kg/ha.
A 3-day period in January of 1988, with lows of -16°C on two nights and a high during the period of only -4°C damaged all cover crops. Blue lupin was killed completely and was consequently dropped from the test. 'Bicolor-1' was dropped from the test in 1989 because even with mechanical scarification, germination was poor. 'Tifwhite-78' proved an excellent cover crop. Three year average maize grain yields indicated that 'Tifwhite-78' supplied approximately 112 kg N/ha to the subsequent maize crop.
The performance of 'Tifwhite-78' in this test prompted further research with this cultivar as an alternative feed grain. The objective was to determine the suitability of white lupin as a component in double-cropping systems for the southeastern United States, and to determine the nitrogen contribution of white lupin, harvested for grain, to summer grain crops in double-cropping systems.
This test was initiated with the planting of 'Tifwhite-78' white lupin and 'Saluda' wheat on a Lucedale sandy loam (Rhodic Paleudult) in southwestern Alabama, on 22 Nov. 1988. In 1989 and 1990, planting dates were 16 and 26 Nov. respectively. In every year, both crops were planted with a grain drill on 20-cm row drill spacing. Wheat was seeded at 100 kg/ha and lupin was seeded at 140 kg/ha. Lupin and wheat were harvested in late June of every year and tropical maize, grain sorghum, or soybean were planted following wheat and lupin harvest, approximately 10 July each year. Row spacing for all summer crops was 75 cm.
Lupin grain yields from three site-years average 1.8, 2.2, and 2.7 Mg/ha. In December 1989, 'Tifwhite-78' was subjected to a consecutive 5 day freeze with lows of -11°, -13°, -16°, -16°, and -4°C. High temperatures during the period did not exceed -2°C. Plants were killed with these freezes; in some cases severe stand loss occurred, but in elevated and well-drained sites, damage was minimal. The performance of 'Tifwhite-78' to date, suggests that white lupin is sufficiently cold hardy to become an alternative winter grain crop in the Southeast.
We are optimistic that winter-hardy white lupin can become a viable component of double-cropping systems in the southeastern United States and we are continuing studies to confirm this hypothesis. A number of problems exist, principally insufficient disease resistance, cold hardiness, and tolerance to wet soils. A strong cooperative research effort currently underway is attempting to resolve these problems in order to develop the full potential of the crop.