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In a three year study (1993, 1994 and 1995) the effect of slurry deposition, landscape position and slope exposure in a grass-covered arid region on the leghemoglobin content (Lb) of pea nodules was studied. Until 1990 this region was used for the deposition of bovine slurry over a period of five years.

The leghemoglobin content of legume nodules is, at different stages of plant development, correlated with the activity of nitrogenase measured by acetylene reduction assay. The total leghemoglobin concentration (Lb/mg nodule) was used to measure the physiological activity of the nodulating Rhizobium leguminosarum by. viciae population. A simple spectroscopic method was adapted to determine the content of leghemoglobin in the nodules of two varieties of Pisum sativum.

The effect of slurry on the nodule leghemoglobin content was more pronounced at the northern exposed slope, where significant different leghemoglobin contents at nonpolluted and polluted sites could be determined in the first two years of sampling. At the southern slope no effect of slurry on the leghemoglobin content of the nodulating population was found, whereas significant differences were determined between slope position and year of sampling. The leghemoglobin content/mg nodule was higher at the southern slope in all three years compared to the northern slope and in 1995 the nodules from all sites had a significant higher leghemoglobin content compared to 1993 and 1994. The relative differences between the individual positions, measured in one year, were reproducible in every year.