Paper mill residuals and compost effects on particulate organic matter and related soil functions in a sandy soil

Amending sandy soils with paper mill residuals (PMR) and/or PMR composts should build soil organic matter pools, thereby increasing carbon and nutrient availability for biologically mediated soil functions. We investigated the effects of PMR and PMR composts on total and particulate organic matter (POM) and their relationships with plant available water (PAW) and mineral nitrogen. From 1998 to 2001, we applied PMR, PMR composted alone (PMR-C), and PMR composted with bark (PMR-B) annually at two agronomic rates to sandy soils in a 3-year vegetable rotation of potato, snap bean, and cucumber. After 4 years, all PMR amendments increased total soil C and N (TC, TN), POM-C, and POM-N 2- to 4-fold, relative to a nonamended control. After 3 years of annual amendment additions, the soil achieved an elevated steady state of POM-C, indicating a net balance between C-input and C-decay. Either TC or POM-C explained greater than 50% of the variation in PAW in years 2 through 4, indicating the functional similarities between the two carbon pools. The first sign of a significant but weak relationship between mineral N and POM-N (R-2 = 15%) or TIN (R-2 = 34%) occurred during the final year of study. Annual additions of PMR and PMR composts produced sustained increases in labile soil C and N pools; however, increases in these OM pools did not translate into short-term nutrient availability in these sandy soils.