Dan M. Sullivan

Maturity and Stability Evaluation of Composted Yard Trimmings

The objective of this research was to evaluate a variety of stability and maturity indices for yard trimmings compost produced in the Puget Sound region of western Washington State. Compost samples were collected periodically during a 133-d composting cycle at a commercial composting facility, showing that indices of compost respiration rate were sensitive indicators of compost quality. All respiration rate indices identified a period of high respiration rates during active composting (first 27 d), and a period of relatively stable respiration rates during the latter part of curing (70 to 133 d). Chemical tests of compost solids showed less promise as maturity indicators, but provided valuable information on final compost quality. Mature yard trimmings compost had a C:N of 12, an NH4-N to NO3-N ratio of less than 4, a cation exchange capacity (CEC) of 400 cmol per kg of compost-C, and a pH between 6.5 and Seed germination tests and sensory tests (color and odor) were of limited value in assessing compost maturity. Fully-cured compost produced with forced aeration had a Solvita CO2 test value of 6 to 7 and a respiration rate via the alkaline trap method of 2 mg CO2-C g compost-C−1 d−1. It reheated less than 2°C in an insulated Dewar flask in a 7 d incubation. Further evaluation and calibration of respiration test protocols for compost quality assurance testing programs are recommended.

Food Waste Compost Effects on Fertilizer Nitrogen Efficiency, Available Nitrogen, and Tall Fescue Yield

and plant-available N release after compost application to land (Sullivan et al., 1998a). Composting of food waste is increasing as composting technologies Composting transforms organic byproducts into drier, improve and as social and environmental pressures demand alternamore uniform, and more biologically stable products tives to disposal in landfills. Few agronomic studies are available to that can act as slow-release sources of plant-available document N availability following food waste compost application. The objectives of this study were (i) to determine food waste compost N. A high-rate compost application also changes the effects on N fertilizer uptake efficiency across a range of N fertilizer soil physical, chemical, and biological properties that rates, (ii) evaluate the effect of food waste composts on grass yield control N availability for many years following applicaand N uptake by tall fescue (Festuca arundinacea Schreb. ‘A.U. tion (Shiralipour et al., 1992; Dick and McCoy, 1993). Triumph’), and (iii) estimate the residual effects of compost applicaUsually, composts supply only a part of the N needed tion on N fertilizer requirements. We used a split-plot design with to produce high-yielding crops; fertilizer N application two compost treatments and a no-compost control as main plots, and is needed for maximum crop yields. NH4NO3 (34-0-0) applied at rates of 0, 17, 34, 50, and 67 kg ha 1 per Most studies on N availability following compost apgrass harvest as subplots. A food waste yard trimmings paper plication have focused on short-term effects. Composts (FYP) compost and a food waste wood waste sawdust (FW) with C:N ratios above 20:1 may reduce crop production compost were applied at rates of approximately 78 Mg ha 1 (870–1000 kg N ha 1 ) before seeding tall fescue. Compost did not affect grass via microbial immobilization of available N during the yield or N uptake in the first year of the study. Compost increased first year after application (Sims, 1990; Shiralipour et grass yield during the second and third seasons after application. Grass al., 1992). For composts with lower C:N ratios, 0 to 25% N uptake increased linearly with fertilizer N application rate in all of the total N usually becomes plant-available during years. Compost did not affect fertilizer N uptake efficiency (the linear the first year after application (Brinton, 1985; Tester, slope describing grass N uptake vs. fertilizer N application). Nitrogen 1989; Dick and McCoy, 1993). The recalcitrant organic fertilizer requirements during the midseason growth period were recompounds present in mature composts probably interduced by 0.22 to 0.37 kg N ha 1 d 1 during the second season after act less with fertilizer N and organic matter N in soil compost application and by 0.13 to 0.26 kg ha 1 d 1 during the third than do most crop residues. Azam et al. (1985) demonseason after compost application. Results of this study suggest that strated that plant residues high in recalcitrant C are N mineralized from compost and N provided by fertilizer can be considered as additive components of N supply for crop growth. usually less active in immobilization–remineralization transformations in soil than residues containing more labile C. The interaction between compost and the cycling of C of food waste is increasing as compostsoil and fertilizer N has been studied over the short ing technologies improve and as social and enviterm with labeled isotopes and factorial blends of comronmental pressures demand alternatives to disposal in post plus fertilizer N. Sikora and Yakovchenko (1996), landfills. Over 100 food waste composting facilities were using 14C-labeled soil organic matter, found that comactive in the USA in 1999 (Glenn and Goldstein, 1999). post did not increase soil organic matter decomposition. Composting in aerated windrows is becoming a widely They found that addition of soil stimulated a small adopted method for rapid composting of wet, putresciamount of compost decomposition and N mineralizable food waste at large composting facilities (Touart, tion. Paul and Beauchamp (1994) reported immobiliza1999; Sikora and Sullivan, 2000). The bulking agent that tion of fertilizer 15N and a very small amount of net N is used to maintain porosity in aerated windrows plays a mineralization in a 12-wk incubation with composted large role in determining final compost N concentration beef cattle manure. Available N from compost was a reliable substitute for up to 50% of fertilizer N supplied D.M. Sullivan, Dep. of Crop and Soil Science, Oregon State Univ., to tall fescue in growth chamber studies (Sikora, 1998; Corvallis, OR 97331; D.R. Thomas, Dep. of Statistics, Oregon State Sikora and Enkiri, 1999). Univ., Corvallis, OR 97331; A.I. Bary, S.C. Fransen, and C.G. Cogger, Because composts contain stabilized organic matter, Dep. of Crop and Soil Sciences, Washington State Univ., Puyallup, WA 98371. Contribution #11550 from Oregon State Univ. Agric. Exp. Abbreviations: ANR, apparent N recovery by tall fescue for midseaStn. Received 13 Dec. 2000. *Corresponding author (Dan.Sullivan@ son growth period; CEC, cation exchange capacity; FYP, compost orst.edu). derived from mixture of food waste yard trimmings paper; FW, compost derived from mixture of food waste wood waste sawdust. Published in Soil Sci. Soc. Am. J. 66:154–161 (2002).

Nitrogen Availability Seven Years After a High-Rate Food Waste Compost Application

Long-term effects of compost application are expected, but rarely measured. A 7-yr growth trial was conducted to determine nitrogen availability following a one-time compost application. Six food waste composts were produced in a pilot-scale project using two composting methods (aerated static pile and aerated, turned windrow), and three bulking agents (yard trimmings, yard trimmings + mixed paper waste, and wood waste + sawdust). For the growth trial, composts were incorporated into the top 8 to 10 cm of a sandy loam soil at application rates of approximately 155 Mg ha−1 (about 7 yd3 1000 ft2). Tall fescue (Festuca arundinacea Schreb. ‘A.U. Triumph’) was seeded after compost incorporation, and was harvested 40 times over a 7-yr period. Grass yield and grass N uptake for the compost treatments was greater than that produced without compost at the same fertilizer N rate. The one-time compost application increased grass N uptake by a total of 294 to 527 kg ha−1 during the 7-yr. field experiment. The greatest grass yield response to compost application occurred during the second and third years after compost application, when annual grass N uptake was increased by 93 to 114 kg ha−1 yr−1. Grass yield response to the one-time compost application continued at about the same level for Years 4 through 7, increasing grass N uptake by 42 to 62 kg ha−1 yr−1. Soil mineralizable N tests done at 3 and 6 yr. after application also demonstrated higher N availability with compost. The increase in grass N uptake accounted for 15 to 20% of compost N applied after 7-yr. for food waste composts produced with any of the bulking agents. After 7-yr, increased soil organic matter (total soil C and N) in the compost-amended soil accounted for approximately 18% of compost-C and 33% of compost-N applied. This study confirmed the long-term value of compost amendment for supplying slow-release N for crop growth.

Fertilizer nitrogen replacement value of food residuals composted with yard trimmings, paper or wood wastes

Composting offers an opportunity to recycle food waste as a soil amendment. A three year growth trial was conducted to determine the fertilizer nitrogen (N) replacement value of food waste composts for cool season perennial grass production. Six composts were produced in a pilot-scale project with two composting methods (aerated static pile and aerated, turned windrow). The aerated, turned windrow method simulated “agitated bay” composting systems, which utilize routine mechanical agitation. Compost bulking agents included yard trimmings, yard trimmings + mixed paper waste, and wood waste + sawdust. Finished composts had Kjeldahl N concentrations ranging from 10 to 18 g N/kg. For the growth trial, composts were incorporated into the top eight to 10 cm of a sandy loam soil at application rates of approximately 155 Mg/ha (about 7 yd3/1000 ft2). Tall fescue (Festuca arundinacea Schreb. ‘A.U. Triumph’) was seeded after compost incorporation, and was harvested repeatedly at a late vegetative growth stage (Apri...

Stability Evaluation of Mixed Food Waste Composts

As interest in food waste composting grows, so does the need for proven composting methods. Stability testing has been proposed as a compost quality assurance tool. We conducted this study to: (i) to evaluate the efficacy of simple outdoor composting methods in producing a compost with a low, stable decomposition rate, and (ii) to determine the reliability of simple, 4-h compost stability evaluation methods. Composting was conducted outdoors in winter and spring in Eugene, Oregon without moisture addition. Mixed food waste was combined with screened dairy solids and ground yard trimmings. Sawdust was used to cover windrows for the first 27 d of composting. Compost windrow temperatures remained above 55°C for 30+ d. Carbon dioxide evolved with several 4-h test methods was strongly correlated (r2 > 0.7) with CO2 evolved using a 48-h test. A limited-turn windrow (LTW) composting system produced compost with slightly greater stability than a passively aerated windrow (PAW) composting system. Food waste compost samples had a low CO2 evolution rate after 71 to 99 d using either composting system. Compost CO2 evolution rate at 25°C decreased with composting time, reaching approximately 1 to 4 mg CO2-C g compost C−1 d−1 for the PAW method and 0.5 to 2 mg CO2-C g compost C−1 d−1 for the LTW method. Putrescible organic matter in food waste was effectively decomposed in outdoor windrows using composting methods that did not employ forced aeration, self-propelled windrow turners, or manufactured composting vessels. Several 4-h stability tests showed promise for implementation as quality assurance tools.

Predicting Biosolids Application Rates for Dryland Wheat across a Range of Northwest Climate Zones

We evaluated dryland wheat (Triticum aestivum L.) response to biosolids applications in the inland Pacific Northwest and compared agronomic application rates predicted from yield curves with those predicted from Extension guidance. We applied biosolids rate treatments during the fallow year in 10 on‐farm experiments and determined grain yield, protein, and postharvest soil nitrate. Nitrogen (N) rates were calculated from Extension guidance and compared with biosolids agronomic rate estimates based on yield regressions generated for each site. Eight of the 10 sites had quadratic yield responses. The agronomic biosolids rate at the responsive sites averaged 315 kg ha−1 more grain than the farmer inorganic N rate. At responsive sites, a mean biosolids application rate of 4.7 dry Mg ha−1 (226 kg total N ha−1) was required for 95% of maximum grain yield. Results showed that Extension fertilizer guidance together with calculations for biosolids available N gave reasonable estimates for biosolids application rates.

Comparison of Disturbed and Undisturbed Soil Core Methods to Estimate Nitrogen-Mineralization Rates in Manured Agricultural Soils

Ion exchange resin / soil cores are a common in situ approach to estimating soil nitrogen (N) mineralization rates. However, no studies compare the two common methods of core preparation (disturbed and undisturbed). The objective of our study was to compare N mineralized and soil temperature in disturbed versus undisturbed cores of manured agricultural soils. Undisturbed cores were prepared by driving aluminum tubes (25 cm long with 10 cm inner diameter) into soil, removing the tubes, and then inserting an ion-exchange resin bag beneath the soil at the bottom of the tube. Disturbed cores were prepared with the same materials, but soil was excavated, mixed, and then filled into tubes fitted with ion-exchange resin bags at the bottom. Soil from six agricultural fields (five of which had more than 10 years of regular dairy manure application) was incubated over four time periods during summer and winter. A total of 13 soil / incubation-period combinations were tested. Disturbed cores tended to have more N mineralized than undisturbed cores (P < 0.10), especially in cores prepared with the lowest clay content soil. However, variability of N mineralized was lower in disturbed cores than undisturbed cores for 11 of the 13 soil / incubation periods. This lower variability was significant in two of the four incubation periods (P < 0.10). There was little difference in mean soil temperatures in disturbed versus undisturbed cores or within cores versus outside but adjacent to cores. However, in summer, the daily temperature range inside cores was significantly greater than the temperature range in soil outside cores (P < 0.01).

Chemical Characteristics of Custom Compost for Highbush Blueberry

Recent development of markets for blueberry (Vaccinium corymbosum L.) produced under Organic certification has stimulated interest in production of composts specifically tailored to its edaphic requirements. Blueberry is a calcifuge (acid-loving) plant that responds favorably to mulching and incorporation of organic matter into soil. Many composts are high in pH and soluble nutrients, and may not be suited to blueberry. This chapter describes recent improvements in developing chemical criteria for composts that indicate potential suitability for blueberry. The experimental work, which was conducted in western Oregon, USA, confirmed that acidic pH (<5.5) is the most important characteristic needed in a custom compost for blueberry. Composts with pH < 6 are rare, so a testing protocol to quantify the pH buffering capacity of compost (CBC) and the quantity of acidity needed to reduce compost pH to 5.0 was developed. Median compost buffering capacity (n = 36) was 0.20 mol H+/kg/pH unit, and median elemental S (So) addition required for acidification to pH 5 was 8 g So/kg, assuming full reaction of So to H+. In compost acidified with So to a final pH of 5–6, EC was increased 1.6 fold, accompanied by increased solubility for K and Na (1.3–1.4×); P, Ca, and Mg (3.2–3.6×); and SO4-S (5.2×). Blueberry plants accumulated K supplied by compost, accompanied by reduced plant uptake of Mg, reduced growth, and possible Mg deficiency. Compost acidification to below pH 6 improved blueberry plant growth and Mg uptake. We conclude that compost can be used to increase soil organic matter for blueberry, but that compost N must be limited to low analysis values (total N < 20 g/kg) in order to avoid problems with high pH, EC, and excess K. Because all compost feedstocks that met USDA-Organic certification requirements needed acidification to reach the desired pH level for blueberry (<5.5), future research should focus on economical, safe, and reliable methods for compost acidification that are acceptable under Organic certification rules.

Slow-Release Nitrogen from Composts: The Bulking Agent is More Than Just Fluff

One of the goals of byproduct co-utilization is to produce products with increased value, and the amount of slow-release nitrogen (N) supplied by composts for plant growth is one component of compost value. To evaluate the effect of bulking agents on the amount of slow-release N derived from composts, we conducted a three-year field trial with a forage-type tall fescue (Festuca arundinacea Schreb. ‘A.U. Triumph’). Composts were prepared for the field trial from mixtures of food residuals (vegetables, meat, fish, dairy, and bakery by-products) with three bulking agents. Food residuals (33 g N/kg) were bulked with yard trimmings (11 g N/kg), yard trimmings + mixed waste paper (7 g N/kg), and wood chips + sawdust (1 g N/kg). After mixing, the food residual/bulking agent mixtures were composted in a turned windrow supplied with forced air for 70 days, then cured without forced air for 36 days. At the end of curing, total N concentrations in screened compost (< 11 mm) were 17 g N/kg for yard trimmings, 14 g N/kg for yard trimmings + paper, and 8 g N/kg with wood chips + sawdust bulking agent. For the field trial, 155 Mg/ha of compost was incorporated to a depth of 10 cm in a sandy loam soil. Tall fescue was seeded the day after compost application and was harvested 15 times over a three-year period to measure compost effects on grass yield and N uptake. Composts consistently increased yield and grass N uptake in the second and third year after application, demonstrating their slow-release N value. Cumulative apparent N recovery (ANR) over the three-year trial ranged from 7 to 11 % of the compost total N applied. Cumulative ANR was 282 kg N/ha for yard trimmings, 242 kg N/ha for yard trimmings + paper, and 113 kg N/ha for wood chips + sawdust bulking agent. Replacement of wood chips + sawdust bulking agent with yard trimmings more than doubled compost slow-release N value. Thus, yard trimmings are a valuable feedstock when developing compost products with slow-release N value.

Organic Production Systems in Northern Highbush Blueberry: I. Impact of Planting Method, Cultivar, Fertilizer, and Mulch on Yield and Fruit Quality from Planting through Maturity

A long-term trial was established in Oct. 2006 in western Oregon to identify organic production systems for maximum yield and quality in highbush blueberry (Vaccinium corymbosum L.). The planting was transitional during the first year after planting and was certified organic during fruit production (2008–16). Treatments included plantingmethod (on raised beds or flat ground), fertilizer source (granular feather meal or fish solubles), and rate (‘‘low’’ and ‘‘high’’ rates of 29 and 57 kg·ha N during establishment, increased incrementally as the planting matured to 73 and 140 kg·ha N, respectively), mulch [sawdust, yard debris compost topped with sawdust (compost + sawdust), or black, woven polyethylene groundcover (weed mat)], and cultivar (‘Duke’ and ‘Liberty’). Mulches were replenished, as needed, and weeds were controlled throughout the study. Raised beds resulted in greater yield than flat ground during the establishment years but had less effect on yield once the plants weremature. After 9 years, cumulative yield was 22% greater on raised beds than on flat ground in ‘Liberty’ but was unaffected by plantingmethod in ‘Duke’. Cumulative yield was also 10% greater with feather meal than with fish solubles, on average, and 4% greater with the low rate than with the high rate of fertilizer. ‘Duke’ was particularly sensitive to fertilizer source and produced 35% less yield overall with fish solubles than with feather meal. By contrast, there was relatively little effect of fertilizer source or rate on yield in ‘Liberty’. In five of 9 years, yield was 8% to 20% greater with weedmat than with sawdust or compost + sawdust. Mulch type had no effect on cumulative yield of ‘Duke’, but cumulative yield of ‘Liberty’ was 11% greater with weedmat than with sawdust or compost + sawdust. Soil temperature was warmer under weedmat than under sawdust, and plants on raised beds covered with weed mat required more irrigation than those grown on flat ground mulched with sawdust. ‘Duke’ produced heavier, larger, and firmer berries with lower total soluble solids (TSS) than ‘Liberty’. However, other treatment effects on berry quality were relatively small and inconsistent. For example, berry weight was greater on raised beds than on flat ground, on average, but only by 3% (0.06 g/berry). Plants on raised beds also produced berries with slightly lower TSS than those on flat ground (15.2%and 15.7%, respectively, in ‘Liberty’, and 13.1% and 13.3%, respectively in ‘Duke’). There was no effect of fertilizer source or rate on TSS in ‘Liberty’ (15.5% on average), whereas in ‘Duke’, TSS was highest when fertilized at the high (13.7%) or low (13.4%) rate of fish, and was lower when using feather meal (12.9% and 13.1% for low and high rate, respectively). Plants fertilized with fish produced firmer fruit than with feather meal in five of the 7 years in which the measurements were taken. Also, fertilization with the higher rate of either product increased berry firmness comparedwith the low rate in six of the 7 years. The impact ofmulch was inconsistent through the study period. On average, ‘Duke’ berries were softest when fertilized with the low (173 g·mm deflection) and high (176 g·mm) rates of feathermeal andwere the firmest with the high rate of fish (182 g·mm). In ‘Liberty’, the low rate of feather meal produced softer fruit (157 g·mm) than the other fertilizer treatments (162 g·mm on average).When this study was initiated in 2006, the most common organic production system in this region was raised beds with sawdust mulch and fertilizing with a high rate of fish solubles. For this production system, yield for mature plants in our study (2014L16) was the equivalent of 8.9L12.3 t·ha in ‘Duke’ and 11.8L23.7 t·ha in ‘Liberty’. However, when plants were grown on raised beds with weed mat and fertilized with the high rate of feather meal, yield increased to 10.2L19.3 t·ha, depending on year, in ‘Duke’. By contrast, there was little effect of production system on yield of mature ‘Liberty’ plants. These yields, particularly for the best-performing treatment combination in ‘Duke’, are similar to what are observed in commercial conventional fields or organic farms using similar management practices. Our results showed that choice of organic production system can have significant impact on yield and economic costs and returns. The Pacific northwestern United States is an important growing region for northern highbush blueberry (Vaccinium corymbosum L.). According to recent U.S. surveys, this region accounted for 20% of the total conventional area of highbush blueberry (U.S. Department of Agriculture, 2014) and 49% of the total organic area (U.S. Department of Agriculture, 2010). Organic blueberry production has increased in this region because of strong consumer demand, price premiums of 20% to 200% over conventional fruit, and a dry summer climate, which reduces the potential incidence for weeds, insect pests, and leaf and fruit diseases (DeVetter et al., 2015; FernandezSalvador et al., 2017; Strik, 2014). However, there were some challenges specific to organic production that needed to be addressed, including greater production costs and inputs (particularly for fertilization and weedmanagement), limited Organic Materials Review Institute (OMRI)-approved options for disease and insect control, and potential or perceived reduced yields of organic plantings and associated returns (Strik, 2014). In 2006, the production guides available for organic northern Received for publication 5 June 2017. Accepted for publication 1 July 2017. The authors value the assistance of Gil Buller and Emily Vollmer, former Faculty Research Assistants at the North Willamette Research and Extension Center, OSU and all of the members of our industry advisory board.We appreciate the funding support provided by the Oregon Blueberry Commission, Washington Blueberry Commission, Northwest Center for Small Fruits Research, and the USDA National Institute of Food and Agriculture (Formula Grant no. OREI 2008-04443). Corresponding author. E-mail: bernadine.strik@ oregonstate.edu. HORTSCIENCE VOL. 52(9) SEPTEMBER 2017 1201 highbush blueberry in North America were based on anecdotal information (Krewer and Walker, 2006; Kuepper and Diver, 2004). There was little research at that point comparing organic production strategies in blueberry, and most of the production research done in conventional blueberry systems was not applicable to organic systems. Highbush blueberry is typically planted on raised beds. Raised beds improve soil drainage (Strik, 2007), limit compaction (Magdoff and Van Es, 2010), reduce incidence of root pathogens such as Phytophthora (Bryla and Linderman, 2007), and improve efficiency of machine harvest (Strik and Buller, 2002). However, planting on flat ground can be beneficial to root growth in southern highbush blueberry (complex hybrids based largely on V. corymbosum and V. darrowiiCamp.) likely due to increased soil moisture and reduced soil temperature during the fruiting season (Spiers, 1995). Furthermore, mechanical weed-control methods are more effective on flat ground than on raised beds (Sciarappa et al., 2008; B. Strik, personal observation). Weed management is critical for successful production of blueberries (Pritts et al., 1992; Strik et al., 1993), but chemical herbicide options available for organic systems are expensive and limited and usually are not very effective on established perennial weeds (Julian et al., 2012; Larco et al., 2013a). Other forms of weed control such as organic mulches, propane flaming, string trimming, and hand weeding are often used instead (Burkhard et al., 2009; Granatstein and Mullinix, 2008; Krewer et al., 2009; Sciarappa et al., 2008). Organic mulches provide additional benefits in highbush blueberry, including increased yield and plant growth (Clark and Moore, 1991; Goulart et al., 1997; Karp et al., 2006; Kozinski, 2006; Krewer et al., 2009; Savage, 1942; White, 2006). Douglas fir (Pseudotsuga menziesii M.) sawdust is commonly used to mulch blueberry plantings in Oregon, Washington, and British Columbia, but sawdust has become expensive in the region (Julian et al., 2011a), and it tends to immobilize a considerable amount of the N applied from fertilizers (White, 2006). Some growers are using compost in addition to sawdust to provide additional nutrients and organic matter (Gale et al., 2006; Larco et al., 2014). Municipal yard debris compost is readily available in many production regions and may be suitable for commercial blueberry production (Sullivan et al., 2014). Weed mat (perforated landscape fabric) is approved for use as a weed barrier by the United States Department of Agriculture (USDA) Organic National Program (USDA-AMS-NOP, 2011), and because of economic advantages, it has been adopted by both organic and conventional blueberry growers (Julian et al., 2012; Strik and Vance, 2017). However, increased soil temperature under the weed mat can reduce plant growth (Neilsen et al., 2003;Williamson et al., 2006) and yield (Krewer et al., 2009). Larco et al. (2013a) reported that northern highbush blueberry grew less with weed mat than with sawdust mulch by the end of the first two growing seasons; however, the plants had greater yield with weed mat in the second year, which was the first season of fruit production. In addition to weed management, availability and affordability of fertilizers are of critical importance for the economical production of organic blueberry (Strik, 2014). Fish solubles and feather meal are common fertilizers used by organic blueberry growers. Fish solubles are typically applied by fertigation through the drip irrigation system, especially when weed mat is used and other application methods are less practical or more expensive. Feather meal is a granular product applied to the soil surface. Both fertilizers mineralize readily on application and quickly release N and other nutrients (Bar