Pulp and paper mill sludges are produced from primary and secondary treatment of wastes derived from virgin wood fiber sources, recycled paper products, and non-wood fibers. Sludges and sludge composts may be utilized in agriculture to increase soil organic matter, improve soil physical properties, provide nutrients, and increase soil pH. Positive effects of primary, deinking, and low-nutrient combined sludges on soil quality are primarily due to increased soil organic matter, aggregation, water holding capacity, infiltration rate, and cation exchange capacity. Nitrogen and P immobilization are often induced by primary and deinking sludges, but can be overcome by delayed planting, adding N and P, planting of legumes, or composting. Improved crop production obtained with secondary treatment sludges is most often attributable to enhanced nutrient availability, particularly N, but improved soil physical properties are implicated in some studies. Pulp and paper mill sludges and sludge composts are useful soil amendments and plant nutrient sources. Key words: Paper mill sludge, soil physical properties, N and P immobilization, nutrient efficiency, land application

Manure is known to increase soil N₂O emissions by stimulating nitrification and denitrification processes. Our objective was to compare soil-surface N₂O emissions following the application of liquid and solid dairy cattle manures to a loamy and a clay soil cropped to silage maize. Manures were applied in 2 consecutive years at rates equivalent to 150 kg total N ha^-1 and compared with a control treatment receiving an equivalent rate of synthetic N. Soil-surface N₂O fluxes, soil temperature, and soil water, nitrate and ammonium contents were monitored weekly in manured and control plots. From 60 to 90% of seasonal N₂O emissions occurred during the first 40 d following manure and synthetic fertilizer applications, indicating that outside that period one or several factors limited N₂O emissions. The period of higher emissions following manure and fertilizer application corresponded with the period when soil mineral N contents were highest (up to 17 g NO₃⁻-N m^-2) and water-filled pore space (WFPS) was greater than 0.5 m³ m^-3. The absence of significant N₂O fluxes later in the growing season despite high WFPS levels indicated that the stimulating effect of organic and synthetic N additions on soil N₂O production was relatively short-lived. Fertilization of silage maize with dairy cattle manure resulted in greater or equal N₂O emissions than with synthetic N. This was observed despite lower overall soil mineral N contents in the manured plots, indicating that other factors affected by manure, possibly additional C substrates and enhanced soil respiration, resulted in greater denitrification and N₂O production. Silage maize yields in the manured soils were lower than those receiving synthetic N, indicating that the N₂O emissions per kilogram of harvested biomass were greater for manures than for synthetic N. Our results also suggest that the main source of N₂O was nitrification in the loam and denitrification in the clay soil. There was no clear difference in N₂O emissions between liquid and solid manures. The variable effects of liquid and solid manure addition reported in the literature on soil N₂O emissions likely result from the variable composition of the manures themselves as well as from interactions with other factors such as soil environment and farming practices. A better characterization of the availability of manure C and N is required to assess the impact of manure application on soil N₂O emissions under field conditions. Key words: Greenhouse gases, N₂O, maize, manure

Few studies have assessed the common, yet unproven, hypothesis that an increase of plant nitrogen (N) uptake and/or recovery efficiency (NRE) will reduce nitrous oxide (N2O) emission during crop production. Understanding the relationships between N2O emissions and crop N uptake and use efficiency parameters can help inform crop N management recommendations for both efficiency and environmental goals. Analyses were conducted to determine which of several commonly used crop N uptake-derived parameters related most strongly to growing season N2O emissions under varying N management practices in North American maize systems. Nitrogen uptake-derived variables included total aboveground N uptake (TNU), grain N uptake (GNU), N recovery efficiency (NRE), net N balance (NNB) in relation to GNU (NNB(GNU)) and TNU (NNB(TNU)), and surplus N (SN). The relationship between N2O and N application rate was sigmoidal with relatively small emissions for N rates <130 kg ha-1, and a sharp increase for N rates from 130 to 220 kg ha-1; on average, N2O increased linearly by about 5 g N per kg of N applied for rates up to 220 kg ha-1. Fairly strong and significant negative relationships existed between N2O and NRE when management focused on N application rate (r2 = 0.52) or rate and timing combinations (r2 = 0.65). For every percentage point increase, N2O decreased by 13 g N ha-1 in response to N rates, and by 20 g N ha-1 for NRE changes in response to rate-by-timing treatments. However, more consistent positive relationships (R2 = 0.73-0.77) existed between N2O and NNB(TNU), NNB(GNU) and SN, regardless of rate and timing of N application; on average N2O emission increased by about 5, 7, and 8 g N respectively, per kg increase of NNB(GNU), NNB(TNU), and SN. Neither N source nor placement influenced the relationship between N2O and NRE. Overall, our analysis indicated that a careful selection of appropriate N rate applied at the right time can both increase NRE and reduce N2O. However, N2O reduction benefits of optimum N rate-by-timing practices were achieved most consistently with management systems that reduced NNB through an increase of grain N removal or total plant N uptake.

Source materials and manure management may affect compost nutrient availability to plants. A laboratory experiment was conducted to determine the impact of these factors on the N and P release from 23 on-farm and 6 industrial composts. Composts were mixed with the Ap horizon of an Arago sandy loam (Humo-Ferric Podzol), at 200 mg N kg⁻¹, and incubated for 13 wk in glass jars at 35 °C. The soil mineral N content at the end of incubation was the highest from poultry litter, sheep manure, horse manure and vegetable residue sources whereas the fresh solid, beef and young dairy manure composts resulted in high N immobilization. The release of N from the compost organic N fraction was in most cases negative. The soil Mehlich-3 P content at the end of the incubation period was higher from the poultry litter than from any other sources, whereas P was strongly immobilized from week 1 to week 13 in the fresh solid, beef and young dairy manure compost amended soils. Septic tank sludge compost was the least efficient N and P source among industrial products whereas the others showed N and/or P release comparable to most on-farm composts. In dairy manure compost, use of wood in bedding, turning compost windrow, increasing composting duration and sheltering material against precipitation all reduced P immobilization during incubation. Organic N mineralization in soil was only significantly increased by composting duration. This study indicated that the short-term N and P potential nutrient value of composts are dependent upon compost source materials and manure management, and should be based on their inorganic N and P content. Key words: Composting, farm manure management, N and P mineralization