. 2002. Hay mulching to reduce runoff and soil loss under intensive potato production in northwestern New Brunswick, Canada. Can. J. Soil Sci. 82: 249-258. Soil erosion by water associated with potato production in northwestern New Brunswick has been identified as one of the most severe soil degradation problems affecting soil quality in Canada. The objectives of this study were to evaluate the effectiveness of applying various rates of hay mulch following potato (Solanum tuberosum L.) harvest in reducing runoff and soil loss rates under northwestern New Brunswick climatic and soil conditions and to determine the impact of the various hay mulch application rates on potato yield. Wischmeier-like runoff-erosion plots (10 m wide by 30 m long) on a Holmesville gravelly loam soil were used. Annual hay mulch application rates of 0.00, 2.25, 4.50 and 9.00 t ha -1 wet mass were evaluated under continuous up-and-downslope potato production on 8 and 11% slopes between October 1995 and October 1999. During the study period, annual precipitation was lower than normal. Calculated rainfall erosivities were 102, 66, 73 and 133% of the value typically used for conservation planning in this region (1276 MJ mm ha -1 h -1 ). Seventy-three percent of the average annual erosivity for the 4-yr period was associated with storms occurring in June, July, August and September. Hay mulching at rates of 2.25, 4.50 and 9.00 t ha -1 conserved on average 13, 18 and 28 mm of June to September precipitation, respectively. Mean annual soil losses were reduced to 14, 7 and 2% of the control (5.6 t ha -1 ) by the 2.25, 4.50 and 9.00 t ha -1 treatments, respectively, on the 11% slope and to 43 and 24% of the control (2.0 t ha -1 ) on the 2.25 and 4.50 t ha -1 treatments, respectively, on the 8% slope. Eroded sediment silt, clay and organic matter (OM) contents were 1.6, 1.9 and 2.3 times the content of the surface soil at the experimental site. Mulching at rates as low as 2.25 t ha -1 reduced nutrient losses of NO 3 -N and available P, K, Ca and Mg to 26, 18, 28, 20 and 24% of control, respectively, on the 11% slope, and to 81, 50, 82, 66 and 77% of control, respectively, on the 8% slope. However, levels of nutrient losses from the controls were low to begin with (2.0, 0.4, 2.8, 10.9 and 1.6 kg ha -1 of NO 3 -N, and available P, K, Ca and Mg, respectively). Both total and marketable potato crop yields from all 2.25 and 4.50 t ha -1 treatments were in excess of 5% greater than their controls; however, only the increases in total yields from the 2.25 and 4.50 t ha -1 treatments and marketable yield from the 4.50 t ha -1 treatment on the 8% slope were significantly greater at P < 0.05. Yield of potato on the 9.00 t ha -1 treatment showed a consistent increase in total yield over the 4-yr period, going from 80% of control in 1996 to 127% of control in 1999, indicating a possible improvement in soil productivity. Hay mulching at rates up to 9.00 t ha -1 did not increase the incidence of disease or other defects. Hay mulching was found to be an effective...
