Nutrient management plans require that fertilizer equivalents of manures and composts be used in determining the total nutrient application to soils. The P nutrient content of manure composts has not been studied as extensively as N. In a growth chamber study using 15‐cm pots, a Codorus silt loam soil (Fluvaquentic dystrochrepts) with less than 10 mg kg −1 . Mehlich‐3 extractable P was amended with poultry litter compost (PLC) or triple superphosphate (TSP) at rates of 0, 25, 50, 100, and 150 kg P ha −1 . Nitrogen was supplied to be uniform across all treatments, taking into account the N mineralization rate of PLC. Fescue ( Festuca arundinacea Schreb) was grown and harvested three times over 103 d. Yield of fescue was curvilinear related to rate of amendment, but yield was not affected by PLC or TSP. Models describing yield changes with rate were different for TSP and PLC. Phosphorus uptake was statistically the same for both treatments, and a single quadratic equation described P uptake with rate. These data indicate that PLC added to soils on a total P basis provided the same amount of fertilizer equivalents as TSP. The use of composted manure as a N source narrows further the plant available N/P ratio from that recorded in manures because N is immobilized and P is not. To use manure compost as source of P, more fertilizer N would be required to satisfy crops needs than if manure was used as a P source.

Nutrient management plans require an accurate assessment of P fertilizer additions to soil. The fertilizer equivalents of manures and composts must be estimated in order to comply. A previous study comparing triple superphosphate(TSP) to poultry litter compost (PLC) as a source of P for fescue indicated that overall they were equal, but when N became limiting during the final harvest, PLC supplied more P to fescue than TSP at comparable rates. A subsequent study was initiated to determine if P from PLC was more available to fescue than TSP when N was not limiting. Sassafras soil was amended with PLC and TSP at rates of 0, 50, 100 and 150 kg ha(-1). Nitrogen was supplied to be uniform across all treatments taking into account the N mineralization rate of PLC. Two harvests of fescue were taken and analyzed for yields and P uptake. Nitrogen was added to all treatments at the original application rate of 120 kg ha(-1) and two more harvests plus roots were collected. Yields were affected by harvest date but not by P rate or source of P. P uptake was affected by date and rate but not source of P. The P uptake response to PLC and TSP was curvilinear and linear respectively, but within the range of P application rates used, the source of P was not a significant factor in P uptake by fescue. Based on the current study testing the effect of unlimited N, addition of supplemental N did not affect P supply from either source. Poultry litter compost is considered equal to TSP in supplying P to fescue and N availability did not affect these conclusions.

Phosphorus-based nutrient management requires that all sources of P added to fields, including manures, must be accounted for in crop production plans. Nearly 13% of U.S. broiler production occurs in the MidAtlantic region, which generates 720,000 tons of manure annually. Use, treatment, or manure disposal options are important issues in dealing with large volumes of manure; transforming the manure to compost and utilizing it off-farm is one viable utilization option. A study to evaluate plant-available P in poultry litter compost (PLC) compared with triple super phosphate (TSP) was conducted in a growth chamber using fescue (Festuca arundinacea Schreb). Phosphorus amendments from 0 to 150 mg P kg−1 soil were added to Sassafras soil (typic Hapludults, fine-loamy, siliceous, mesic). Nitrogen rates were constant over all P treatments at 150 kg N ha−1. Fescue was harvested three times during an 84-day study, and clippings, as well as roots and crowns at the termination, were analyzed for P content. Cumulative dry weight of fescue clippings was the same for both TSP and PLC and did not change with increased P application from 0 to 150 kg P ha−1 soil. These data suggest that the Sassafras soil was not deficient in P (Mehlich 3 extractable P was approximately 125 mg P ha−1) and that the N application rate of 150 kg N ha−1, which was constant across all P treatments, determined yields. Cumulative phosphorus uptake was the same for PLC and TSP but, in this case, was linearly related to P application rate. At the 84-day harvest, greater P uptake was recorded for 100 and 150 kg PLC-P ha−1 rates than for all other treatments, which suggested that organic compounds in the PLC may be blocking adsorption sites and/or releasing soluble P with time. Phosphorus uptake by roots and crowns was approximately equal to cumulative P uptake of clippings. Statistical analysis indicated no effect of P source or rate on P uptake by roots and crowns, but only two of four replicates were harvested. Because PLC was equal to TSP in supplying P to fescue, composting of poultry litter does not seem to affect P availability in the same manner as it affects N. Compost application based on crop N needs and N availability will result in greater plant-available P additions than if uncomposted poultry litter is added.

Composts are considered low analysis fertilizers because their nitrogen and phosphorus content are around 1% and the organic nitrogen mineralization rate is near 10%. If compost is added to agricultural land at the N requirement of grain crops (40 – 100 kg N ha−1), application rates approach 40–100 mg ha−1. Much lower rates may be advisable to avoid rapid accumulation of growth limiting constituents such as heavy metals found in some composts. Combining low amendment rates of composts with sufficient fertilizer to meet crop requirements is an appealing alternative which (a) utilizes composts at lower rates than those needed to supply all the crop N requirement, (b) reduces the amount of inorganic fertilizer applied to soils, and (c) reduces the accumulation of non-nutrient compost constituents in soils. A study was conducted to compare the effects of blends of biosolids compost (C) with 15N urea(U) or 15NH4 15NO3 (N) fertilizers to fertilizer alone on tall fescue (Festuca arundinacea L.) growth and N uptake. Blends which provided 0, 20, 40 or 60 mg N kg−1 application rate as compost N and 120, 100, 80 or 60 mg N kg−1 as fertilizer N, respectively, were added to Sassafras soil (Typic Hapludults). Fescue was grown on the blends in a growth chamber for 98 days. Fescue yields recorded by clippings taken at 23, 46 and 98 days and roots harvested after the 98-day clipping increased with increasing fertilizer level for both NH4NO3 and urea and with or without compost. Nitrogen uptake by fescue responded similarly to yield with increases recorded with increasing fertilizer levels with or without compost. Paired comparisons based on cumulative 98-day clippings data showed that yields from blends were equal to yields from fertilizer treatments containing the same percentage of fertilizer as the blends. These data indicated that compost did not provide sufficient plant-available N to increase yields or N uptake. None of the blends equaled 120 mg N kg−1 fertilizer rate except for 100 mg NH4NO3-or urea-N kg−1 −20 mg compost-N kg−1blends. The data suggest that biosolids compost blended with fertilizer at a rate of 2–6 mg ha −1 did not supply sufficient additional available N to increase yields or N uptake over those of fertilizer alone.

Combining composts with sufficient fertilizer to meet crop requirements has several benefits over the use of compost as a sole N source, including reduced accumulation in soils of heavy metals, salts, or P. The objective of this research was to End blends of compost and fertilizer that would equal the yield and N uptake of N fertilizer. Biosolids compost-fertilizer blends made to equal 100 mg available N kg(-1) were compared with urea or NH4NO3 fertilizer. Zero to 50% of the blend's available N came from biosolids compost; the remainder came from fertilizer. N-15- labeled fertilizer was used to determine the proportion of N uptake attributed to fertilizer, Fescue (Festuca arundinacea Schreb,) was used as the indicator plant. Compost did not increase the efficiency of NH4NO3 fertilizer. The amount of available N provided by urea-compost blends was less than the amount provided by NH4NO3-compost blends, Urea-compost blends that had 17 to 50% fertilizer equivalents from compost equaled 100% urea. Blends of 50% NH4NO3 and 50% biosolids compost available N or 67% NH4NO3 and the equivalent of 33% biosolids compost N produced greater yields and N uptake by fescue. N-15 analysis suggested that NH4NO3 fertilizer stimulated soil and/or compost mineralization producing more N than predicted from incubation studies of compost N mineralization rates. However, previous studies showed that soil mineralization was not affected by compost, which leads to the conclusion that fertilizer stimulated compost mineralization. Urea did not affect compost similarly, possibly because of a larger active N pool in urea compost blends compared with NH4NO3 compost blends.

Composts are considered low-analysis fertilizers because their N and P content is from 1 to 2% and the N mineralization rate is near 10%. If compost is added to agricultural land at the N requirement of grain crops (40 to 100 kg ha(-1)), application rates approach 40 to 100 mt ha(-1) Much lower rates may be advisable to avoid accumulation of constituents such as heavy metals found in some composts. Combining low-amendment rates of composts with sufficient fertilizer to meet crop requirements is an appealing alternative which (i) utilizes composts at lower rates than those needed to supply all of the crop N requirement, (ii) reduces the amount of inorganic fertilizer applied to soils, and (iii) reduces the accumulation of nonnutrient compost constituents in soils. A study was conducted to compare the effects of blends of biosolids compost (C) with urea (U) or NH4NO3(N) fertilizers with fertilizer alone on tall fescue (Festuca arundinacea L.) growth and N uptake, Blends that provided 0, 16.7, 33, or 50% of the 100 mg N kg(-1) application rate as compost N and 100, 83.3, 67, or 50% as fertilizer N were added to Sassafras soil (Typic Hapludults). Fescue was grown on the blends in a growth chamber for 109 days. Fescue yields decreased linearly with decreasing fertilizer level for both NH4NO3 and urea and with or without compost. Nitrogen uptake by fescue was different for fertilizer- than for compost-amended pots, depending on the rate of fertilizer added. Paired comparisons based on cumulative 109-day data indicated yields from NC67 (67% NH4NO3-N, 33% compost N) and NC83 equaled the yield of N100, Similarly for blends containing urea, UC67 yield was equal to U100. Nitrogen uptake from NC83 was equal to N100, but N uptake from NC67 was significantly less than from N100. Nitrogen uptake by UC67 was significantly less than U83 which had a greater mean N uptake than N100. The data suggest that compost N can replace one-third of the fertilizer N required by fescue without decreasing yield. Because the mineral N plus the mineralization of organic N that comprises the compost N portion of the blends did not equal that of the corresponding fertilizer alone, constituents other than N contributed to yields from the compost fertilizer blends.

A pronase-sensitive, 14 kDa component of bacteroids of Bradyrhizobium japonicumI-110ARS was identified and characterized using monoclonal antibodies. This component was weakly synthesized or was missing in bacteroids of a unique Nod- Fix- mutant, ARS2525. Both the 14 kDa component and poly-β-hydroxybutyrate (PHB) were located in the same protein peak after sucrose density gradient separation of lysed bacteroids. Thirty-five-day-old bacteroids of B. japonicumI-110ARS contained up to 10 times more PHB than B. japonicumARS2525 bacteroids. Immunocytochemistry of ultra-thin nodule sections showed that the component was associated with PHB granules in the bacteroids, possibly with the limiting membrane around the granules. This observation implies that the component may be similar to other storage lipid body proteins. Whether low synthesis of the 14 kDa component or low PHB content was a cause, a consequence or related to the Fix- phenotype was not established.