Legume-wheat rotation in dryland cropping systems in eastern Colorado

Abstract

In the Great Plains of the United States, hard red winter wheat (Triticum aestivum L.) is the dominant dryland crop. A fallow period of approximately 14 months is used to increase soil water storage and enhance yield. This technique has a low precipitation storage efficiency and produces soil degradation. Thus, replacing part of the summer fallow by a crop can increase the water use efficiency of the system. Legumes are interesting because of their forage and grain production, and their potential N input for the subsequent crop. Four legume cultivars: Austrian winter pea (Pisum sativum L. var. arvense), Profi pea (Pisum sativum L.), and two soybeans (Glycine max. L. Men), were grown during the spring and summer previous to a wheat crop during 1998, 1999 and 2000 in eastern Colorado. The objectives were: a) to evaluate their forage and grain production and their N uptake and water use under three utilization alternatives (forage, grain and green manure), b) to determine their effect on subsequent wheat yield. Averaged across three years the forage production of Austrian winter pea, Profi pea and soybean was 1873, 831 and 1550 kg ha-1, respectively. Grain yield was 832, 1014, and 1521 kg ha-1 for Austrian winter pea, Profi pea, and soybean respectively. The total N returned to the soil after termination of the forage treatment was less than 15 kg ha-1. When used for green manure, the N input was 72 kg ha'1 for Austrian winter pea, 29 kg ha-1 for Profi pea and 66 kg ha-1 for soybean. The N input from the grain management was similar to the green manure treatment. The water use of the legumes depended on the precipitation during the growing period, the dry matter production and the utilization of the legume. In 1999 wheat yield after legumes for forage, grain and green manure was respectively 23, 51 and 29 percent lower than wheat yield after fallow. In 2000, wheat yield did not decrease after legumes for forage, but after legumes for grain and green manure it was respectively 34 and 17 percent lower than after fallow.