Effect of nitrogen amendments on microbial biomass, above-ground biomass and nematode population in the Negev Desert soil

Nitrogen amendments (0, 25, 50 and 100 kg NH4NO3/ha) were used to study the responses of primary production, microbial biomass and nematode population in desert soil. The study was conducted in the Israeli Negev Desert, a reg ion characterized by low and randomly distributed rainfall. Over a 1-year s tudy period, nitrogen amendments resulted in a significant (p < 0.01) incre ase in soil microbial biomass. Soil microbial biomass also increased concom itantly with the increase in soil organic matter. The number of free-living nematodes in the soil increased with the increase in soil moisture, rangin g from 43,000 individuals per square metre at the end of the summer to 351, 000 individuals per square metre during the rainy season. No significant co rrelation was found between the nitrogen treatments and the nematode popula tion, whereas a significant positive correlation was found between the nitr ogen amendments and the above-ground biomass (r(2) = 0.94, p < 0.03). The n itrate proportion of the total soluble nitrogen in the soil also increased with the increase in soil moisture. This study provides baseline data for n itrogen amendments on soil microbial status, as well as insights into the i mportance of nitrogen in fertility in arid environments. (C) 1999 Academic Press.