Effects of sowing date and nitrogen fertilizer on forage yield, nitrogen- and water-use efficiency and nutritive value of an annual triple-crop complementary forage rotation

Complementary forage rotation (CFR) systems based on non-limiting inputs of fertilizer nitrogen (N) (similar to 600 kg N ha-1) are perceived as uneconomic. An experiment was carried out in Australia to investigate the effects of rates and timing of N fertilizer and sowing date on yield, nutrient-use efficiency and nutritive value of a triple-crop (maize, forage rape, field peas) CFR system. Treatments were early- and late-sown maize grown with 0 or 135 kg fertilizer N ha(-1) pre-sowing (N1) and 0, 79 or 158 kg N ha(-1) post-sowing (N2). Forage rape was sown with 0 or 230 kg N ha-1 (N3) and field peas without N. Application of fertilizer N at N1, N2 and N3 increased CFR yield from 28.5 to 48.8 t dry matter (DM) ha(-1) and irrigation water-use efficiency (IWUE) from 3.4 to 6.1 t DM per megalitre. Increase in yield and IWUE of CFR occurs at the expense of nitrogen-use efficiency (NUE) as applications of N at N1, N2 and N3 decreased NUE of CFR from 524 to 91 kg DM kg-1 N. Nutritive value, particularly metabolizable energy content of all forages, was similar among N treatments, and interactions between treatments were minimal. Results indicate that increase in NUE of CFR may occur at the expense of reduced yield, but increased IWUE need not compromise the yield of this CFR system.