Effect of nitrogen fertilizer rate, herbicide rate, and soil disturbance at seeding on the productivity of a wheat-pea rotation

Rotational productivity is a function of the rotational crops and their interactions, as well as the management employed. Understanding the functioning of the overall production system, as well as its component parts, may contribute to improved management. Effects of nitrogen fertilizer rate (25, 50, 75, 100 kg N ha-1 as urea) and herbicide rate (66 or 100% of recommended) applied to wheat, and of the level of soil disturbance at seeding, on the productivity and N status of a 2-yr rotation of spring wheat (Triticum aestivum L.) and field pea (Pisum sativum L.) were assessed over two rotation cycles at two locations in southwestern Manitoba. Management factors typically acted independently to influence the cropping system. In both wheat and pea, high soil disturbance at seeding reduced or tended to reduce plant density in most site-years, resulting in reduced yields in about half of site-years. In 2 site-years where weed pressure was high, wheat yields for high disturbance treatments were less than 60% of low disturbance seeding, demonstrating the importance of adequate plant stands under sub-optimal growing conditions. The herbicide rate applied to wheat had few significant effects on wheat and pea. In most site-years, N fertilization had limited or negative effects on wheat yields due partly to relatively high soil NO3-N levels. Soil NO3-N levels declined over the years of the study, suggesting that N contributions from peas did not exceed crop N removal and/or N losses from the wheat-pea rotation. The N rate applied to wheat typically did not affect pea yields. Key words: Wheat, pea, rotation, herbicide, nitrogen, soil disturbance