Application of dairy manure to forage crops is a viable means of recycling nutrients and minimizing problems with manure storage. The objective of this study was to determine whether forage cropping system or frequent application of liquid dairy manure affected populations of plant-parasitic nematodes. Two forage systems were evaluated: the CBR system was a rotation of temperate corn (Zea mays L.), coastal bermudagrass [Cynodon dactylon (L.) Pers.], and a mixture of rye (Secale cereale L.) and crimson clover ( Trifolium incarnatum L.); and the CCR system was a rotation of temperate corn, tropical corn, and a mixture of rye and crimson clover. Application of liquid manure at 14-day intervals with irrigation water was compared to application of inorganic fertilizer based on crop recommendations. The soil was naturally infested with Helicotylenchus sp., Mesocriconema sp., Paratrichodorus sp., and Pratylenchus spp. Densities of Mesocriconema sp. and Helicotylenchus sp. tended to be greater in CBR plots than in CCR plots, while the reverse was observed for Pratylenchus spp. Densities of Paratrichodorus sp. and Pratylenchus spp. were consistently lower in the manure treatment than in the fertilizer treatment. When averaged across years, numbers per 150 cm3 of soil in manure vs. fertilizer were 79 vs. 159 for Pratylenchus spp. and 8 vs. 16 for Paratrichodorus sp. The other plant-parasitic nematodes were unaffected or inconsistently affected by nutrient source. Additional research is needed to determine the mechanism of nematode suppression when liquid dairy manure is applied regularly to the crop. If ammonia accumulation is involved, then soil type and pH will be important factors in determining the efficacy of the treatment.
