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EN
Field experiments were conducted to assess the effect of time of introduction of maize and cropping pattern on two varieties of soybean in a soybean/maize intercrop in 2007 and 2008 seasons at the University of Agriculture Makurdi. Three periods of introduction of maize were evaluated: (i) planting at the same time with soybean;(ii) introduction of maize two weeks after planting soybean and (iii) introduction of maize four weeks after planting soybean. There were five cropping patterns viz: (i) soybean variety Samsoy-2 planted sole (ii) soybean variety TGX 1448-2E planted sole (iii) maize variety DMR-ESR-Y planted sole (iv) Samsoy -2 intercrop with maize and (v) TGX1448-2E intercrop with maize. The experiment was a split plot laid on complete randomized block design replicated three times. Results obtained revealed that there was no significant effect of time of introduction of maize on any soybean parameter observed. Yield and yield components of soybean indicated significant effect of cropping pattern (P < 0.01) with number of pods per plant and grain yield. Grain yield and number of pods per plant decreased in intercrop with soybean variety Samsoy-2 having the highest number of pods per plant and grain yield. The result on maize indicated that maize planted sole was significantly (P < 0.01) taller than intercropped maize, there was significant (P < 0.01) effect of time of introduction of maize and cropping pattern on maize plant height, ear length, ear diameter, survival and barrenness percentage and grain yield. The Land Equivalent ratio (LER) values indicated that higher yield advantages were obtained from maize introduced two weeks after planting soybean and maize intercropped with soybean variety Samsoy-2 (1.35) than with soybean variety TGX1448-2E (1.12).
EN
We performed manipulative field experiments to investigate the effects of soil disturbance and exposure to a fungal plant pathogen, Puccinia coronata (Corda), on the establishment and spread of two introduced, cultivated genotypes of perennial ryegrass, Lolium perenne (L.). The two cultivars of L. perenne with different levels of susceptibility to P. coronata were introduced to grassland sites to investigate whether a plant cultivar selected to resist a pathogen shows better establishment in semi-natural plant communities than a susceptible cultivar. At two sites where L. perenne was already present, the addition of L. perenne seeds had no significant effect on the shoot biomass of the species, indicating that these populations were not seed limited. Exposure to the pathogen resulted in disease, and infected L. perenne populations showed increased shoot biomass over the course of the 3 year experiment and at harvest the final year, but no effect on seed production. Reproductive allocation was not affected by disease exposure in disturbed plots, but decreased in the presence of disease in undisturbed plots. The increased biomass observed in the semi-natural plant communities when exposed to the pathogen contrasts with the reduced biomass observed in garden experiments when the two cultivars of L. perenne were exposed to pathogen attack. The surprising positive effect of P. coronata on biomass in semi-natural communities indicates that processes here are more complex than in more intensively managed production systems.
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