Wheat straw treated with 0.5 or 1.0 ml/g
urea-sulfuric acid (1 : 1 acid in water v/v) and incubated
in Protneuf or Woodburn silt loam soils in the
laboratory decomposed faster than nontreated straw
the first 4-6 weeks but at 12 weeks the nontreated
straw had decomposed 25% – 45% more. In a field experiment,
urea-sulfuric acid treated straw, removed at
40-day intervals over 160 days, decomposed faster
than nontreated straw. The differences were attributed
to salt buildup in the laboratory samples, where electrical
conductivities up to 17.6 dS/m were observed. In
the field, leaching removed the excess salts. Nitrification
produced up to 1875 mg NO3-N/kg Portneuf
silt loam soil in the laboratory, indicating that nitrifying
bacteria were not suppressed by the salt. Total
plate counts with no straw were 1.8 x 10^6 microorganisms/g
and with urea-sulfuric acid treated straw were
15.7 x 10^6/g soil after 14 days incubation. The respective
actinomycete counts were 0.3 x 10^6 and 6.7 x 10^6/g
for the no straw and straw-treated soils, respectively.
The urea-sulfuric acid treatments suppressed straw
decomposition in the laboratory and accelerated straw
decomposition in the field

Jackson, T.L.

Smith, J.H.

Northwest Irrigation & Soils Research Laboratory Publications

Decomposition of wheat and barley straw treated with urea-sulfuric acid

USDA - ARS - NWISRL

SoilsBiologyand FertilityofBiol Fertil Soils (1987) 4:199-203© Springer-Verlag 1987Decomposition of wheat and barley strawtreated with urea-sulfuric acidJ.11. Smith l and T. L. Jackson 1 ' 21 USDA-ARS, Snake River Conservation Research Center, Kimberly, ID 83341, USA2 Oregon State University, Corvallis, OR, USASummary. Wheat straw treated with 0.5 or 1.0 ml/gurea-sulfuric acid (1 : 1 acid in water v/v) and in-cubated in Protneuf or Woodburn silt loam soils in thelaboratory decomposed faster than nontreated strawthe first 4-6 weeks but at 12 weeks the nontreatedstraw had decomposed 25% – 45% more. In a field ex-periment, urea-sulfuric acid treated straw, removed at40-day intervals over 160 days, decomposed fasterthan nontreated straw. The differences were attributedto salt buildup in the laboratory samples, where elec-trical conductivities up to 17.6 dS/m were observed. Inthe field, leaching removed the excess salts. Nitrifica-tion produced up to 1875 mg NOF -N/kg Portneufsilt loam soil in the laboratory, indicating that nitrify-ing bacteria were not suppressed by the salt. Totalplate counts with no straw were 1.8 x 10 6 microorgan-isms/g and with urea-sulfuric acid treated straw were15.7 x 106/g soil after 14 days incubation. The respec-tive actinomycete counts were 0.3 x 106 and 6.7 x 106/gfor the no straw and straw-treated soils, respectively.The urea-sulfuric acid treatments suppressed strawdecomposition in the laboratory and accelerated strawdecomposition in the field.Key words: Wheat – Barley – Urea – Sulfuric acid– Straw decompositionSoil moisture and temperature are major factors con-trolling crop residue in the field. Another factor ofmajor importance in crop residue management is Nfertilization. Nitrogen addition to crop residues hasOffprint requests to: J. H. Smithbeen attributed to hasten decomposition in N-defi-cient soil systems and to retard decomposition insystems with adequate to excessive N (Allison andMurphy 1963). Reviews by Bartholomew (1965) andSmith and Peterson (1982) report the past and currentstatus of carp residue decomposition research, withmany citations supporting various theories and factorsaffecting residue decomposition. With present levelsof fertilizer application on most farms, added Nseldom accelerates crop residue decomposition be-cause N is usually adequate for the needs of soilmicroorganisms. Other factors such as temperatureand moisture can limit decomposition to the extentthat N is not a controlling factor. Soil and plant ad-ditives have been promoted in the past for increasingcrop residue decomposition and soil microorganismactivity but most have been ineffective (Smith et al.1961; Weaver et al. 1974). In the western United States,urea has been reacted with sulfuric acid to form aproduct less corrosive than sulfuric acid. This productwith several formulations that contain 10%-28% Nis marketed for spraying on cereal grain straw andother crop residues to aid in digestion and decomposi-tion of the organic residues.This paper reports the effects of urea-sulfuric acidon decomposition of cereal straw in controlled ex-periments in the laboratory, decomposition evalua-tions of the material on straw in the field, and the ef-fects of the compound on total numbers of microor-ganisms and on actinomycetes in the laboratory.Materials and methodsStraw decomposition in the laboratory. Fieldwin soft white springwheat straw (1)-iticum aestivum L.) was treated with 1: 1 v/v ureasulfuric acid in water at 0.5 or 1.0 ml/g straw. The urea-sulfuric acidhad 1 mol urea reacted with 1 mol sulfuric acid and contained0 7 14 21 28 35 42 49 56 63 7q 77 84INCUBATION, daysFig. 1. Carbon dioxide evolved from wheat straw decomposing inPortneuf silt loam soil in the laboratory. • : no acid; x: 0.5 nil acid;: 1.0 ml acid200	 J. H. Smith and T. L. Jackson: Wheat and barley straw decomposition15% N and 17% S. The 0.5 ml/g application was the /east thatwould wet the surface of the ground (<2 mm) straw. A theoreticalN application on a field basis could be as follows: With 5 mgstraw/ha, treated with 0.5 ml 1: 1 urea-sulfuric acid in water wherethe original urea sulfuric acid contained 170 g N/kg, would provideapproximately 300 kg N/ha. The straw was mixed in Portneuf siltloam (course-silty, mixed, mesic, Durixerollic Calciorthids) at ratesof 0.5, 1.0, or 1.5 g straw/100g air dry soil. The urea-sulfuric acidwas mixed with the straw and the appropriate weight of treatedstraw was added to the soil to provide the straw weights desired. The100-g soil samples containing the straw were placed in 1/2-1-bottles,wetted with 18 ml distilled water, and incubated at 26°C. Themoisture content of the soil represented about 80% of 33 kPa(0.33 bar) tension. The flasks were continuously aerated withCO2-free air passing over the soil surface. Carbon dioxide was cap-tured in bottles containing standard 0.1 N NaOH solution. TheNaOH solutions were removed weekly from the incubator, treatedwith 10 ml 10% BaC12 solution, titrated with standard 0.1 N112504solution, and CO2 evolution calculated. All treatments werereplicated 3 times. An air blank was used to determine the smallamount of CO2 in the air supply. Airflow through the sampleflasks was regulated with capillary tubes in the air tubes to theflasks.The soil samples were removed after 12 weeks, air dried, ex-tracted, and analyzed for NO3 using a specific ion electrode(Milham et al. 1970). The pH and electrical conductivity of asaturated paste extract were measured.A second experiment almost identical to the first was run on anoncalcareous Woodburn silt loam soil (fine-silty, mixed, mesic,Aquultic Agrixerolls) from Corvallis, Oregon. Each flask received21 ml water, representing about 80% 33 kPa tension as above. Dif-ferences between treatments were determined by analysis of varianceaccording to LeClerg (1957).Field experiments. Greer, soft white winter wheat (73-ilicumaestivum L.) and a mixture composed of 90% Mal, 10% Hesk,winter barley (Hordeum vulgare L.) straws were coarsely groundthrough a 1-cm screen in a Wiley mill. "Bventy-five-gram sampleswere treated with 0, 0.5, or 1.0 ml urea-sulfuric acid in a 1:1 v/vmixture with water, and placed into fine mesh nylon cloth bags. Thetreatments were replicated 3 times. The bags were buried 20 cm inPortneuf silt loam soil at Kimberly, Idaho, into which 5 mg straw/hahad been incorporated by rototilling to about 20 cm with no N treat-ment. Burial was on 3 May 1985. The bags were removed from thefield plots on 12 June, 22 July, 30 August and 10 October 1985.Adhering soil was removed from the surface of the bags and thebags were dried in an oven at 60°C for several days. The straw wasremoved from the bags and weighed for decomposition measure-ment by weight loss. The straw was analyzed for total N by theKjeidahl procedure of Carter et a]. (1967). Differences in decom-position were determined by analyses of variance (LeClerg 1957).Microorganism numbers. Fielder, soft white spring wheat straw(Tilticum aestivum L.) was treated with urea-sulfuric acid 1: 1 (v/Ii)with water at the rate of 0.5 ml acid/g straw and mixed with 100 gPortneuf silt loam in 1/2-1 flasks. Straw was added to the soil atrates of 0, 0.5, 1.0, and 1.5 g/flask. The soil and straw mixture waswetted with 18 ml distilled water plus 1 mi/g straw. This wasequivalent to 80% of 33 kPa moisture tension. The flasks were in-cubated at 26 °C with a one hole stopper inserted in the neck foraeration. A 10-g soil sample was removed weekly from each of 3replicate flasks, an appropriate dilution series was prepared, and thetotal plate count for microorganisms was made according toWollum (1982). Actinomycetes were enumerated by the method ofWilliams and Wellington (1982). Differences in microorganismnumbers were determined by analysis of variance (LeClerg 1957).Results and discussionStraw decomposition in the laboratoryStraw decomposition as measured by CO 2 evolutionin the laboratory was stimulated by treatment withurea-sulfuric acid during the 1st-4th weeks in Port-neuf silt loam soil (Fig. 1). When 1.0 ml acid was add-ed per gram straw, decomposition was more rapid thanwhen 0.5 g urea-sulfuric acid/g straw was added. Afterthe initial stimulation period, the nontreated strawdecomposed at a more rapid rate than the treatedstraw. The crossover in total C evolved occurred in the4th – fith weeks, with final decomposition at 12 weeksbeing 25% – 45% greater for the nontreated strawthan for the two treated straws. The same results wereobserved for straw decomposition in the Woodburnsilt loam soil except that crossover occurred betweenthe 5th and 8th weeks (Fig. 2). Analyses of varianceshowed differences to be significant at the 95% pro-bability level for acid treatments after the 2nd or 3rdweek. The accumulative C differences with time werealso different. Curves reported in Fig. 1 and 2 arevalues derived for acid treatments. The three straw ap-plications are not presented separately because of thesimilarity in curve shapes.After 12 weeks of incubation, the soil was removedfrom the flasks and extracted for nitrate and electricalconductivity determinations. In both soils, the nitrateC, rngJ. H. Smith and T. L. Jackson: Wheat and barley straw decomposition 	 201C, mg0 7 14 21 28 35 42 49 56 63 70 77 84INCUBATION. daysFig. 2. Carbon dioxide evolved from wheat straw decomposing inWoodburn silt loam soil in the laboratory. • : no acid; x : 0.5 mlacid; o : 1.0 ml acidTable 1. Soil nitrate and electrical conductivity of Portneuf andWoodburn soils following 12 weeks incubation of urea-sulfuric acidtreated wheat straw in the laboratoryStraw (g) Acid (mlig straw)NOg -N (mg/kg) EC (dS/m)0.0 0.5 1.0 0.0 0.5 1.0Portneuf silt loam soil0.5 50 326 755 1.24 5.83 9.661.0 51 640 1370 1.21 8.11 14.871.5 23 923 1875 1.22 11.37 17.63Soil control 67 1,47Woodburn silt loam soil0.5 24 190 162 0.60 3.77 5.131.0 11 182 81 0.51 5.13 7.061.5 4 74 25 0.55 6.65 10.23Soil control 38 0.78values in soils without urea-sulfuric acid treated strawshowed a slight to fairly large immobilization ofnitrogen (Table 1). In the Portneuf soil, both urea-sulfuric acid treatments provided a large amount of Nthat was mineralized and appeared as nitrate.Nitrogen was immobilized in the Woodburn soilwhen treated with straw alone but nitrification occur-red to a limited extent in response to urea-sulfuric acidtreatment. Nitrification was severely limited by acid inthe Woodburn soil with pH decreasing from 5.1 to 4.3in response to urea-sulfuric acid treatment. In con-trast, nitrification in the calcareous Portneuf soil withpH of about 7.5 was not decreased by the acid treat-ment.The electrical conductivity in the Portneuf soil ini-tially was 1.47 dS/m and it increased incrementallywith increasing acid-straw treatments to 17.6 dS/m. Inthe Woodburn soil the original EC was 0.78 dS/m andit increased to 10.23 dS/m with increments of acidstraw.Decomposition of the added straw was decreasedoverall in both soils by the urea-sulfuric acidtreatments. In the Portneuf soil, nitrification was notdecreased by the urea-sulfuric acid straw treatments.In the Woodburn soil were the pH was decreased bythe urea-sulfuric acid treatments, nitrification waslimited. However, it is difficult to separate the effect ofthe urea-sulfuric acid treatment directly from theoverall pH change that occurred in the soil as a resultof the acid straw treatments. It is also probable thataccumulated soluble salts decreased microbial activityand straw decomposition in the latter part of the in-cubation, as evidenced by the large increases in ob-served electrical conductivity. An EC near 18 limitsalmost all crop plant growth and it is likely thatmicrobial respiration is also severely limited by elec-trical conductivity values observed here (Handbook60).Straw decomposition in the fieldGreer soft white winter wheat straw decomposition inthe field for 160 days was about 48% for nontreatedstraw. Straw that was treated with either 0.5 or 1.0 mlurea-sulfuric acid per gram straw decomposed signifi-cantly faster than the nontreated straw, with 58%decomposition occurring in the same time. There wereno differences between the urea-sulfuric acid rates ondecomposition (Fig. 3). The barley straw that was nottreated decomposed about 50% in the 160-day incuba-tion. Urea-sulfuric acid treatment increased strawdecomposition to about 60 070 and again there were nodifferences between the two acid treatments (Fig. 4).Microorganism counts in incubated soilTotal plate counts and actinomycetes were enumeratedweekly in soils amended with four rates of strawtreated with urea-sulfuric acid to determine if soilmicroorganisms numbers were suppressed by thetreatments (Table 2). The analysis of variance showedhighly significant differences. Both total and ac-tinomycetes counts increased as the straw addition rateincreased at nearly all of the sampling dates. Bacteria202	J. H. Smith and T. L. Jackson: Wheat and barley straw decompositionFig. 3. Weight loss in winter wheat straw decomposing in the fieldfor 160 days in the summerFig. 4. Weight loss in winter barley straw decomposing in the fieldfor 160 days in the summerTable 2. Total plate counts and actinomycetes in Portneuf silt loamsoil treated with urea-sulfuric acid treated straw, incubated in thelaboratoryAcid-treatedstraw in soil(g/kg)Incubation days14 21 28 35 42 58 71 85 100Total plate counts'0 1.8 1.2 2.2 1.0 1.9 0.3 1.4 0.8 0.6 1.25 6.6 7.0 8.8 8.3 3.8 7.0 9.4 7.3 6.0 7.110 9.6 8.2 11.0 9.5 9.0 5.8 9.4 7.8 7.9 8.715 15.7 14.7 17.0 11.3 11.8 7.0 8.3 10.7 9.9 11.8Actinomycetes a0 0.3 0.6 0.6 0.7 1.2 LO 1.4 0.9 0.6 0.85 0.3 1.2 1.3 1.8 1.4 1.3 2.1 1.6 0.2 1.210 0.4 1.5 1.8 1.8 2.6 1.7 2.5 1.6 1.8 1.715 6.7 2.2 2.2 2.7 3.2 1.7 2.0 2.0 2.0 2.7a For microorganisms per gram dry soil multiply by 10 6ANOVA	Total plate counts	 ActinomycetesF	FStraw	 178.57*"	2219.97 • **Dates	 7.66***	14.86***Straw x dates	 3.10* •	35.21***Rep	 1.03	1.20*" F values are significant at 99.91/4 probabilityas measured in the total plate count increased from 1.8to 15.7 million/g soil during the 1st week of incuba-tion. During the same time actinomycete counts in-creased from 0.3 to 6.7 million/g soil with incrementalstraw additions. No straw without acid treatments wasincluded in the experiment because of laboratorylimitations. Therefore, no direct comparisons could bemade of microorganism numbers in straw with andwithout urea-sulfuric acid. But the relatively highnumbers of microorganisms that were found indicatedthat the straw and soil mixtures were populated withlarge numbers of microorganisms. The high nitrifica-tion that was observed in the Portneuf silt loam soilincicated that nitrifying microorganisms were notlimited in the calcareous soil.ConclusionsLaboratory experiments showed that urea-sulfuricacid accelerated straw decomposition initially but at12 weeks decomposition was slower than in nontreatedstraw. The slowing of decomposition was probablycaused by salt accumulation in the soil from the acid.In the field urea-sulfuric acid enhanced straw decom-position throughout the 160-day experiment in thesummer. Nitrification was not limited by the acidtreatments in calcareous Portneuf soil but was slowedin Woodburn slightly acid soil. Total plate counts forsoil microorganisms and numbers of actinomyceteswere greatly increased in soil treated with urea-sulfuricacid treated straw. Test data indicate than the acidtreatment was not particularly damaging to the soilmicroorganisms. While the treatment of straw withurea sulfuric acid may not be an economically feasiblemethod of accelerating straw decomposition in thefield, the treatments work rather satisfactorily, eventhough more N is applied than is desirable in applyingsufficient acid to wet the surface of the straw. A widerratio of urea-sulfuric acid to water, 1 : 5 or 1 : 10,would wet the straw with less nitrogen being appliedand would be a more economical treatment thatshould be evaluated. Finally, this experiment demon-strates that care must be exercised in extrapolating lab-oratory experiments to field conditions.J. H. Smith and T. L. Jackson: Wheat and barley straw decomposition 	 203References1. Allison FE, Murphy RM (1963) Comparative rates of decom-position in soil of wood and bark particles of several species ofpine. Soil Sci Soc Am Proc 27:309-3122. Bartholomew WV (1965) Mineralization and immobilization ofnitrogen in the decomposition of plant and animal residues. In:Bartholomew WV, Clark FE (eds) Soil nitrogen. Agronomy10:285-306. Am Soc Agron, Madison, WI3. Carter JN, Bennett OL, Pearson RW (1967) Recovery of fer-tilizer nitrogen under field conditions using N 15 . Soil Sci SocAm Proc 31:50-564. LeClerg EL (1957) Mean separation by the functional analysisof variance and multiple comparisons. ARS-20-3, 33 pp, ARS,USDA5. Milham PJ, Awad AS, Pauli RE, Bull JH (1970) Analysis ofplants, soil and waters for nitrate by using an ion-selective elec-trode. Analyst 95:751-7576. Smith JH, Peterson JR (1982) Recycling of nitrogen throughland application of agricultural, food processing, andmunicipal wastes. In: Frank J, Stevenson (eds) Nitrogen inagricultural soils. Agronomy No. 22, Am Soc Agron, Madison,WI, pp 791-7967. Smith JH, Allison FE, Soulides DA (1961) Evaluation ofPhosphabacterin as a soil inoculant. Soil Sci Soc Ant Proc25:109-1118. United States Salinity Laboratory (1954) Diagnosis and im-provement of saline and alkali soils. Agricultural handbook No.60, United States Department of Agriculture9. Weaver RW, Dunigan EP, Parr IF, Hiltbold AE (1974) Effectsof two soil activators on crop yields and activities of soilmicroorganisms in the Southern United States. SouthernCooperative Series Bulletin No. 189. A Joint Regional Publica-tion of the Agricultural Experiment Stations of boas,Alabama, Georgia, Kentucky, Louisiana, North Carolina,Oklahoma and the United States Department of Agriculture10. Williams ST, Wellington EMH (1982) Actinomycetes. In: PageAL (ed) Methods of soil analysis, part 2. Chemical and micro-biological properties, 2nd edn. Agronomy 9, part 2. ASAMadison, WI, pp 969-98711. Wollum AG II (1982) Cultural methods for soil micro-organisms. In: Page AL (ed) Methods of soil analysis, part 2.Chemical and microbiological properties, 2nd edn. Agronomy9, part 2. ASA Madison, WI, pp 781-802Received May 19, 1986

https://eprints.nwisrl.ars.usda.gov/id/eprint/481/1/605.pdf

Decomposition of wheat and barley straw treated with urea-sulfuric acid

Abstract

Similar works

Full text

Available Versions

Northwest Irrigation & Soils Research Laboratory Publications

USDA - ARS - NWISRL