Long-Term Soil Ecosystem Studies

Though legumes are beneficial in crop rotations, there is limited information on how tillage system-crop sequence interactions influence crop yield and N production. To see if biomass and N yields in short-term legume-based rotations under zero tillage (ZT) and low-input (LI) production methods can equal those in cereal monocultures under ZT and conventional tillage (CT), field experiments were conducted in Alberta, Canada, from 1989 to 1992 at Ellerslie (Typic Cryoboroll soil) and Breton (Typic Cryoboralf). Treatments at each site consisted of (i) two 4-yr rotations, each with the same crop sequence but different tillage methods, and (ii) four continuous barley treatments in 2 x 2 factorial combination of tillage and fertilizer N. The crop sequence was barley (Hordeum vulgare L.)-barley and field pea (Pisum sativum L.) intercrop-barley-fababean (Viciafaba L.). At Ellerslie, tillage for weed control and seedbed preparation was either CT-LI or ZT. At Breton, one rotation used the LI approach ; the second used deep tillage (DT). Weeds on CT and ZT were controlled with either pre- or postemergence herbicides. No herbicides were applied to LI treatments at either site or to the DT treatment at Breton. Yields of barley following legumes under ZT were similar to those of fertilized continuous barley. With nonchemical weed-control methods, weed competition reduced yields of barley following legumes by 24% compared with fertilized continuous barley. The increased fababean yield measured under DT was associated with improved rooting conditions and water extraction. The equivalent N-fertilizer value of legume residues with similar weed-control levels averaged 19 kg ha[-1] Except for the LI system, legume-based rotations produced, over the 4-yr cycle, amounts of N equivalent to continuous cereal systems. Resource use efficiency of legume-based rotations, as measured by net-N yields, was equivalent to continuous systems at Breton, but somewhat reduced at Ellerslie.

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils. q 2003 Elsevier Science Ltd. All rights reserved.