Abstract: This study assessed the impact of time and method of liquid hog manure applications on nutrient availability and eventually related threats to groundwater quality in a silt loam soil (orthic-humo-ferric Podzol) cropped to forage grasses. Manure N (Nm) was supplied either in fall (NmF) or in spring (NmS), and overhead broadcast- (O) or low-level broadcast-applied (L) on perennial forage hay. A total of 4 combinations of manure treatments were then tested in the spring: NmFl, NmFo, NmSl, and NmSo. No P or K was added. Two control treatments included N00 (0 N, 0 P, and 0 K) and conventional N34 (48 kg N ha^-1 and P and K upon soil P and K tests). After the first cut, an additional amount of 48 kg N ha^-1 was applied from N34 to all N treatments. The same N amount was applied from Nm to NmS treatments in separated plots. Consequently, eight N management regimes were studied on the 2nd cut including N00+N00, N34+N34, NmSl+NmSl, NmSl+N34, NmSo+NmSo, NmSo+N34, NmFl+N34, NmFo+N34, the 1st term referring to the fall or spring application and the 2nd one being the N source and amount applied after the 1st cut. A randomized complete block design and three replicates were used. The results indicated that the effect of Nm was not significantly different from that of N34 with regards to the yields of the first harvest. An averaged yield of 2866 kg ha^-1 was harvested. The second cut yield was very low under all the treatments due to the drought. The treatments also had an equivalent effect on the soil quality including for NmS+NmS regime. Therefore, hog manure could be applied twice in a season on this field because of the low P saturation ratio of the soil. P content in feed under N34 was significantly lower than that under Nm or NmS. The same is true for K. No differences were observed with regards to nitrogen content. On most of monitored parameters, the effects of NmS vs NmF and NmO vs NmL were equivalent, except for N uptake for which NmL was significantly lower than NmO.