Effect of composted and non-composted pulp fibre residue waste as soil amendment on soil moisture, potato yield, and soil nitrogen

Composted (CP) and non-composted Pulp Fibre (PF) wastes were added as organ ic amendments to a sandy loam soil. In the years 1997 and 1998, completely randomized plots were under continuous rotation of Russet Burbank variety p otatoes. Application rates of each organic amendment were 45 t ha(-1) (CP2 and PF2) and 90 t ha(-1) (CP4 and PF4). Soil moisture retention curves for the amended soils showed a 5% to 10% increase in moisture retention. In the 1997 crop, a significantly (p<0.05) higher total yield was obtained from P F2, CP2, and CP4 treatments compared with the PF4 treatment. Lower, but not significant, total yield of potato for all treatments and tuber sizes were obtained from the 1998 growing season versus that of 1997. However, in the 1998 crop, a significantly (p<0.05) higher marketable yield and yield of t ubers sizes exceeding: 80 mm were observed for each of PF2 and PF4 treatmen ts, compared with the CP2 or CP4 treatments. In the 1997 cropping year, PF2 and PF4 treatments were significantly (p<0.05) lower in diseased tubers th an CP2 or CP4. In the 1998 crop, a general drop in incidence of diseased tu bers was observed, in particular within the PF4 treatment, which was signif icantly lower in diseased tubers than CP2 or CP4. At tuber set and bulking stages of the crop, the total soil nitrogen of the amended soil was higher (immobilized) in 1998 than in 1997. A reduction in soil C:N ratio equivalen t to 4 to 9 units occurred in amended soils by the end of harvest in the se cond year. In general, higher NO3-N levels (mineralization of N) were found in soils in 1997 than in 1998. In 1997, NO3-N was immobilized at higher am ounts in the soil of the PF4 treatment, while in 1998 NO3-N was scarcely av ailable in the soil of the CP4 treatment. In general, addition of organic m aterial significantly stimulated the soil microbial biomass C content and m icrobial respiration.