Recovery of nitrogen by spring barley following incorporation of 15N-labelled straw and catch crop material

Agriculture Ecosystems & Environment ELSEVIER

Agriculture, Ecosystems and Environment 49 (1994) 115-122

Recovery of nitrogen by spring barley following incorporation of 15N-labelled straw and catch crop material Ingrid K. Thomsen *'a, Erik S. Jensen b aDepartment of Plant Nutrition and Physiology, Research Centre Foulum, P.O. Box 23, DK-8830 Tjele, Denmark bplant Biology Section, Environmental Science and TechnologyDepartment, Riso National Laboratory, DK-4000Roskilde, Denmark

(Accepted 18 January 1994)

Abstract The recovery by spring barley (Hordeum vulgate L. ) of nitrogen mineralized from 15N_labelled straw and ryegrass material was followed for 3 years in the field. The effects of separate and combined applications of straw and ryegrass were studied using cross-labelling with 15N. Reference plots receiving ~SNH4~SNO3were included. Plant samples were taken every second week until maturity during the first growing season and at maturity in the two following years. Incorporation of plant material had no significant influence on the above-ground dry matter yield of the barley. The barley recovery of N derived from straw was not significantly different whether straw was incorporated alone or in combination with ryegrass material. The mean recovery of straw N was 4.5% in the first barley crop and 2.7% and 1.1% in the second and third crop. During the first growing season, recovery of ryegrass N in the barley was higher when the catch crop material was incorporated without straw, but the differences were only significant at one sampling date. At maturity 7.8% and 10.2% of the ryegrass N was recovered in the barley crop, when ryegrass was incorporated with or without straw, respectively. Mean recoveries of ryegrass N were 2.3% in the second year and less than 1% in the third year after incorporation. Recovery of mineral fertilizer in the year of application was relatively low (29-40%), probably due to long periods of spring drought in all 3 years. The recovery of N from residual mineral fertilizer was in the second and third barley crop similar to the recovery of N from incorporated plant residues.

1. Introduction In northwest Europe losses o f nitrate by leaching occur from arable soils. Excessive losses are unacceptable f r o m e n v i r o n m e n t a l and resource points o f view, and various m e t h o d s to reduce losses have been proposed. Mineralization o f nitrogen from soil organic matter is the main source *Correspondingauthor.

o f nitrate leached during a u t u m n and winter ( M a c d o n a l d et al., 1989). Adjustments o f agricultural practises are needed to reduce these leaching losses. Catch crops (e.g. ryegrass) which take up nitrate during a u t u m n and thus conserve nitrogen in the soil-plant system, have been shown to reduce nitrate leaching considerably (Martinez and Guiraud, 1990; T h o m s e n et al., 1993 ). Leaching losses also decrease after incorporation o f cereal

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straw (Jarvis et al., 1989), due to immobilization of mineral nitrogen during decomposition (Christensen, 1985; Thomsen, 1993b). Straw incorporation and catch crop growing in the same field may become more widespread. In Denmark field straw burning is not allowed and 65% of the acreage has to be kept covered during winter. The effects of combined catch crop cultivation and straw incorporation on nitrate leaching may be cumulative. Catch crops take up mineral N in autumn and after incorporation of the catch crop and straw, N immobilization may occur during decomposition. In order to predict correctly the amount of mineral fertilizer N needed for the succeeding crop it is important to obtain more information on mineralization rates of N from plant materials added to soil. The residual nitrogen effect of ryegrass and straw incorporated individually has been examined previously (Powlson et al., 1985; Wagger et al., 1985; Jensen, 1991b, 1992; Thomsen, 1993a). However, if cultivation of a catch crop and straw incorporation are combined, the pattern of nitrogen mineralization may be different. The presence of an easily decomposable substrate has been shown to accelerate decomposition of the more resistant plant components such as lignin (Kirk et al., 1976 ). A catch crop of low C/N ratio may act as an easily available carbon and energy source which may enhance the mineralization of straw N. The aim of this study was to compare the fate of nitrogen from cereal straw and ryegrass, incorporated in the field separately or together with applied mineral fertilizer. A subsequent paper will present results on nitrate leaching from a parallel lysimeter experiment.

2. Materials and methods

2.1. Site and soil The experiment was carded out at Askov Experimental Station in Denmark. Mean annual temperature is 7.7°C, the lowest and highest monthly means being - 0 . 2 ° C and 15.5°C, respectively. Annual precipitation is 968 mm. The

soil is a Typic Hapludalf, coarse loamy to fine loamy, mixed mesic (Moberg and Dissing Nielsen, 1986). The topsoil contains 1 l°/o clay, 16% silt, 22% fine sand and 48% coarse sand. The total N content is 0.18% and organic C content 2.0%.

2.2. Production oflSN-labelled plant materials Spring barley (Hordeum vulgare L. cultivar 'Grit') was sown in a separate 20 m 2 field plot on 18 April 1989. Italian ryegrass (Lolium multiflorum L. cultivar 'Turgo') was undersown in the barley. To ensure uniform spreading of ~SN the plot was divided into 20 smaller plots which all were fertilized on 19 May with a mixture of KlSNO3 and 15NH~SNO3 dissolved in water. The barley received 10.2 g N m - 2 in total, with a mean atom percentage 15N of 18.04, 1.2 g P m - 2 and 3.1 g K m - 2 . During spring 1989 the barley was irrigated three times with 20 mm water. At maturity barley was harvested by hand on 14 August 1989 and the straw chopped ( 1-7 cm). Ryegrass was harvested on 20 November. The labelled straw was transferred to the experimental microplots after 1 day, labelled ryegrass after 2 days.

2.3. Experimental procedure Fourteen microplots were established in a field previously grown with cereals. Board frames ( 1.75 m × 1.75 m, 20 cm deep) were installed in the ground with the top being level with the surrounding soil surface. The microplots were sown with barley on 18 April 1989 and fertilized with unlabelled N ( 10 g m-2), P ( 1.2 g m -2) and K (2.4 g m-2). In the plots planned for catch crop incorporation, Italian ryegrass was sown the same day. The experimental design is shown in Fig. 1. The soil between the plots was sown to barley. Barley was harvested by hand on 14 August with minimal disturbance of the catch crop. On 16 August labelled straw from the separate field

I.K. Thomsen, E.S. Jensen / Agriculture, Ecosystems a nd Environment 49 (1994) 115-122

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Sowing (B: barley, R: ryegrass)

Harvest of barley (R: Straw removal, *S: 15 N-straw application, S: return of unlab, straw)

Harvest of ryegrass (*R:lSN-ryegrass application, R: return of unlab, ryegrass)

Sowing (B: barley receiving unLabelled fertilizer, *B: barley receiving 15N-fertilizer)

Cuttings every second week (6 x one row) Harvest (nine rows) Sowing (B: barley receiving unlabelled fertilizer, *B: barley receiving tSN-fertilizer)

Harvest (eight rows) Sowing IB: barley receiving unlabelled fertilizer, *B: barley receiving 15N-fertilizer)

Harvest (eight rows)

Fig. 1. Diagramof the experimentaldesign. plot and unlabeUed straw from the microplots were applied (Fig. 1 ). In plots receiving straw only, straw was buried in the soil at a depth of 5 cm. In plots with ryegrass, straw was spread in the ryegrass. The Italian ryegrass in the microplots was harvested on 20 November. Fresh, unchopped ryegrass from the separate field plot and the microplots was returned to the microplots on 21 November (Fig. 1 ). Ryegrass harvested in the microplots where labelled barley straw had been applied in August, was returned to the same plots and supplemented with unlabelled ryegrass so that all ryegrass plots received similar amounts of N. Some chemical characteristics of the applied plant material are shown in Table 1. Application rates for barley straw and ryegrass are shown in Table 2. All microplots were cultivated by hand to a depth of 15 cm on 21 November. In the first experimental year all microplots were sown to barley on 23 March 1990 (Fig. 1 ). Plots previously supplied with labelled straw or labelled catch crop material received unlabelled NH4NO3 ( l0 g N m - 2 ) . Reference plots receiv-

ing neither straw nor ryegrass received the same N-rate in 15NH~SNO3 (5.139 atom %15N). All treatments were fertilized with 1.2 g P m -2 and 2.4 g K m - 2. Every second week from 15 May to 24 July (six times), one row of barley was cut at the soil surface. The remaining part of each plot (nine rows) was harvested at maturity on 13 August. The plots were dug by hand in November. The second and third experimental year ( 1991 and 1992 ) plots were resown to barley and fertilized as in 1990 (Fig. 1 ). Each year new reference plots were fertilized with tSNH~SNO3. At maturity barley from the area disturbed by the cuttings in 1989 was harvested separately. To minimize any border effect from the previous years, only eight rows were harvested from the undisturbed area, the ninth row was cut together with plants from the disturbed area. Only plants from the undisturbed parts were analyzed. The barley plants were separated into grain and straw and dried (80°C). The experimental design was a randomized complete block with two replicates. The data were analyzed using the General Linear Model procedure of Statistical Analysis Systems Limited

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Table 1 Some chemical characteristics of the applied plant material

5N-labelled straw UnlabeUed straw ~5N-labelled ryegrass Unlabelled ryegrass

Total C (%ofDM)

Total N (%ofDM)

Atom% ~SN

Dry matter ~

44.4 45.0 42.5 41.1

0.5 0.6 2.1 2.0

8.665 2.841 -

62.7 61.3 18.7 18.7

(%)

~At the time of incorporation.

Table 2 Application rates for straw and ryegrass in autumn 1989 Treatment

15N-straw 15N-straw + ryegrass 5N-ryegrass ~SN-ryegrass + straw

Straw

Plant residue N applied

Ryegrass

Labelled z

Unlabelled ~

Labelled I

Unlabelled z

Labelled 2 source

Unlabelled 2 source

306.9 306.9 0.0 0.0

0.0 0.0 0.0 306.9

0.0 0.0 100.1 100.1

0.0 101.7 0.0 0.0

1.57 1.57 2.10 2.10

0.0 2.28 0.0 1.96

Total residue N applied ( g N m -2)

1.57 3.85 2.10 4.06

~Grams DM m -2. 2Grams N m -2.

(1985) and means were tested according to Fisher's least-significant difference.

2.4. Analytical methods Oven-dry plant material was milled first in a centrifugal mill (Retsch Ultra Centrifugal Mill ZM 1, Dawo Hanoling, Aabenraa) and then in a ball mill (Retsch Ball Mill Type S 1, Dawo Hanoling, Aabenraa). Total N and 15N were determined on a Carlo Erba NA1500 elemental analyzer coupled on-line to an isotope ratio mass spectrometer (Finnigan MAT, Delta) via a variable split interface as described by Jensen (1991a). All ~SN determinations were corrected for 15N background (0.371 atom%lSN ).

3. Results and discussion

Straw spread in the ryegrass catch crop in August 1989 did not influence the dry matter pro-

duction or N uptake in the ryegrass which accumulated between 1.2 and 2.0 g N m -2. At the time ofryegrass incorporation, 1.6% of the straw N was found in the above-ground parts of the ryegrass (data not shown). The dry matter production and N uptake by the spring barley sampled during the first growing season after straw and ryegrass incorporation were not influenced by the different treatments (Fig. 2 (a), (b)). The growth was influenced by a drought during May, when precipitation was only 12 m m (30 year average 55 mm). During this period, the above-ground dry matter production ceased temporarily (Fig. 2 (a)) and the total N uptake decreased in some of the treatments (Fig. 2(b) ). Plant uptake of mineralized straw N was sireflax where straw had been incorporated alone and together with ryegrass (Fig. 2 (c) ). The recovery of ryegrass N exceeded the recovery of straw N, and during most of the growth season recovery of ryegrass N tended to be higher where ryegrass had been incorporated without straw. However,

I.K. Thomsen, E.S. Jensen / Agriculture, Ecosystems and Environment 49 (1994) 115-122 g m -2 A

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Fig. 2. Dry matter yieldand N uptake in springbarley 1990. (A) Dry matter yield, (B ) totalN uptake, (C) recovery of 15N from mineral fcrtilizcrand plant residues, (D) uptake of mineral fertilizerrclativeto totalN uptake (*,~SNH~S NO3; O15N-straw; • 15N.stmw + unlabellcdryegrass;[] iSN.ryegrass; A 15N-ryegrass+ unlabcllcdstraw).

except for one harvest (81 days after sowing) pairwise comparisons between the two treatmcnts showed no significantdifferences in uptake of rycgrass N. The mineral fertilizerN was taken up within a few weeks of application (Fig. 2 (c) ) and itsproportion of totalN in barley decreased during the growing season (Fig. 2 (d)) in accordance with Thomsen (1993a). Grain yield and total N uptake of the barlcy crop harvested at maturity in the firstyear after incorporation of straw and ryegrass tended to bc smaller in the reference plots receiving mineral fertilizeronly (Tables 3 and 4), but significant differences were not observed. In the third year (1992) a prolonged and severe drought period during spring and summer resulted in vcry low dry matter yields and N uptake. Less than 1% of the total N uptake in the barley harvested in the first year (1990) originated from the incorporated straw (Table 4). Incorporation of ryegrass together with the straw did not affect plant uptake of straw N. Mineralized ryegrass N accounted for a slightly higher pro-

portion of total N uptake. In the second and third year the total N uptake originating from the straw and ryegrass decreased further (Table 4). In all 3 years mineral fertilizer N applied in the particular year accounted for less than half of the total N uptake in barley (Table 4). The residual value of fertilizer N in the years following application was very low, and accounted for 2.22.5% and 1.1% of the total N uptake in the second and third year, respectively. The recovery of N from straw and ryegrass in the first barley crop harvested at maturity corresponded to the results from the cuttings, although recoveries of N were slightly lower than the results from the last cutting (Table 5; Fig. 2 (c)). This was probably a result of a border effect during the period of cutting. However, the mutual relationship between the four treatments was unaltered. Each of the 3 years the recovery of straw N was similar with and without combined ryegrass incorporation (Table 5). The ryegrass, therefore, did not enhance the N mineralization from straw

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Table 3 Grain and straw yield in the 3 years of investigation Treatment

~SN-source applied

Ref. 15N-fertilizer Ref. l~N-fertilizer Ref. tSN-fertilizer tSN-straw ~SN-straw+ryegrass ~SN-ryegrass ~SN-ryegrass+straw

1990

1990 1991 1992 1989 1989 1989 1989

1991

1992

Grain~

Straw t

Grain~

Straw~

Grain~

Straw

377 . 388 448 444 429

269 (15) . 308 (15) 341 (2) 335 (63) 360 (30)

528 (88) 476 (16)

437 (45) 400 (34)

467 519 472 469

384 422 410 382

253 216 259 274 283 220 274

196 191 191 221 191 201 206

(34) 2 . (4) (12) (83) (35)

. (58) (41) (45) (18)

(31) (18) (18) (2)

(24) (22) (26) (11) (41) (63) (53)

(10) (3) (69) (1) (12) (13) (72)

1Grams DM m -2. 2Standard error (n = 2 ). Table 4 Total N accumulation in grain and straw Treatment

tSN-source applied

1990 Total crop N (gm -2)

Ref. 15N-fertilizer

1990

Ref. t SN-fertilizer

1991

Ref. t 5N-fertilizer

1992

~SN-straw

1989

t 5N-straw + ryegrass

1989

tSN-ryegrass

1989

' 5N-ryegrass + straw

1989

7.52 (0.07) L 9.01 (0.26) 9.29 (0.19) 9.77 (1.19) 9.78 (1.20)

1991 Amount from applied source g m -2

%of total N

3.5 (0.16) -

46.5

0.07 (0.01) 0.07 (0.01) 0.21 (0.03) 0.16 (0.03)

0.8 0.7 2.2 1.7

Total crop N (gm -2)

1992 Amount from applied source g m -2

%of total N

10.15 (1.29) 8.93 (0.02) -

0.22 (0.02) 4.06 (0.17) -

2.2

8.66 (1.01) 10.38 (0.17) 9.50 (1.10) 9.27 (0.18)

0.04 (0.00) 0.04 (0.01) 0.05 (0.01) 0.04 (0.00)

45.5 0.5 0.5 0.5 0.6

Total crop N (gm -2)

6.17 (0.30) 5.59 (0.57) 6.27 (0.95) 6.78 (0.05) 6.62 (0.53) 5.50 (0.66) 6.56 (0.76)

Amount from applied source g m -2

%of total N

0.07 (0.01) 0.14 (0.00) 2.97 (0.13) 0.02 (0.00) 0.01 (0.00) 0.02 (0.01) 0.01 (0.00)

1.1 2.5 47.3 0.3 0.2 0.3 0.2

Standard error (n = 2 ).

by acting as a growth substrate for the decomposing microflora in soil as was observed by Kirk et al. (1976) for lignin decomposing with or without glucose or cellulose. The recoveries found for straw N agrees with Myers and Paul (1971), but are lower than found in studies of Powlson et al. ( 1985 ), Voroney et al. (1989) and Wagger et al. ( 1985 ). The first barley crop recovered more ryegrass N than straw N. This was expected because of the lower C/N-ratio and content of lignin in rye-

grass. The amount of ryegrass N recovered in the first barley crop in this study was lower than recoveries obtained in previous studies with ryegrass on similar soil types (Jensen, 1992; Thomsen, 1993a). These differences may be caused by the drought in the present study and different experimental conditions. Jensen (1992) and Thomsen (1993a) used plant material that was dried and cut or ground before being mixed into sieved soil. This may have resulted in higher decomposition rates compared with the present ex-

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Table 5 Recovery in grain and straw of applied ~5N Treatment

Ref. t 5N-fertilizer Ref. ~5N-fertilizer Ref. 15N-fertilizer ~SN-straw 5N-straw + ryegrass 5N-ryegrass 5N-ryegrass+straw

15N.source applied

1990 1991 1992 1989 1989 1989 1989

Recovery of ~SN applied (%) 1990

1991

34.5 a 4.5 c 4.4 ¢ 10.2b 7.8b

2.2 b 40.1 a 2.6 b 2.7b 2.4 b 2.1b

1992 0.7 b

1.4b 29.3" 1.2b 0.9 b 0.8 b 0.6 b

Means followed by the same letter within a column are not significantly different (P= 0.05 ).

periment, which was carded out under conditions more closely resembling agricultural practice. Only 29-40% of the mineral fertilizer applied in spring was recovered by spring barley in the year of application. Yet the residual value of mineral fertilizer the second and third year after application was low. Recoveries of mineral fertilizer N were low in all three growth periods compared with other studies (Dressel and Jung, 1990; Powlson et al., 1992; Thomsen, 1993a). The low recoveries are ascribed to drought in spring in all years of investigation. This study showed that uptake of N from incorporated ryegrass exceeded uptake of straw N in the first year after application. However, combined incorporation of the two plant materials did not influence the subsequent plant uptake of N from the individual plant residues. In the second and third barley crop similar recoveries was found for ryegrass N and straw N. The recovery in barley of mineral fertilizer N only exceeded the recovery of N from organic residues in the year of application. This indicates that the residual N was stabilized in soil organic matter or lost from the soil-plant system to the same degree, irrespective the origin of the N. 4. Acknowledgement

This research was financially supported by Ministry of Agriculture, 'Gronne Marker' (Green Fields).

References Christensen, B.T., 1985. Wheat and barley straw decomposition under field conditions: effect of soil type and plant cover on weight loss, nitrogen and potassium content. Soil Biol. Biochem., 17: 691-697. Dressel, J. and Jung, J., 1990. tSN studies of the behavior of fertilizer nitrogen in three different soils (lysimeter trials). J. Agron. Crop Sci., 164: 217-223. Jarvis, S., Barraclough, D., Unwin, R.J. and Royle, S.M., 1989. Nitrate leaching from grazed grassland and after straw incorporation in arable land. In: J.C. Germon (Editor), Management Systems to Reduce Impact of Nitrates. Elsevier Applied Science, London, pp. 110-123. Jensen, E.S., 1991 a. Evaluation of automated analysis of t 5N and total N in plant material and soil. Plant Soil, 133: 8392. Jensen, E.S., 1991 b. Nitrogen accumulation and residual effects of nitrogen catch crops. Acta Agric. Scand., 41: 333344. Jensen, E.S., 1992. The release and fate of nitrogen from catchcrop material decomposing under field conditions. J. Soil Sci., 43: 335-345. Kirk, T.K., Connors, W.J. and Zeikus, J.G., 1976. Requirement for a growth substrate during lignin decomposition by two wood-rotting fungi. Appl. Environ. Microbiol., 32: 192-194. Macdonald, A.J., Powlson, D.S., Poulton, P.R. and Jenkinson, D.S., 1989. Unused fertiliser nitrogen in arable soilsits contribution to nitrate leaching. J. Sci. Food Agric., 46:407-419. Martinez, J. and Guiraud, G., 1990. A lysimeter study of the effects of a ryegrass catch crop, during a winter wheat/ maize rotation, on nitrate leaching and on the following crop. J. Soil Sci., 41: 5-16. Myers, R.J.K. and Paul, E.A., 1971. Plant uptake and immobilization of 1SN_labelled ammonium nitrate in a field experiment with wheat. In: Nitrogen-15 in Soil-Plant Studies. IEAE, Vienna, pp. 55-64.

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M~berg, J.P. and Dissing Nielsen, J., 1986. The constituent composition of soils from Danish State Agricultural Research Stations. Tidsskrift Planteavls Specialserie, S 1870, 37 pp. (in Danish). Powlson, D.S., Hart, P.B.S., Poulton, P.R., Johnston, A.E. and Jenkinson, D.S., 1992. Influence of soil type, crop management and weather on the recovery of ~SN-labelled fertilizer applied to winter wheat in spring. J. Agric. Sci. Camb., 118: 83-100. Powlson, D.S., Jenkinson, D.S., Pruden, G. and Johnston, A.E., 1985. The effect of straw incorporation on the uptake of nitrogen by winter wheat. J. Sci. Food. Agric., 36: 26-30. Statistical Analysis Systems Institute, Inc., 1985. SAS/ STATT M Guide For Personal Computers, Version 6 Edition. SAS, Cary, NC, 378 pp. Thomsen, I.K., 1993a. Nitrogen uptake in barley after spring

incorporation of ~SN-labelled Italian ryegrass into sandy soils. Plant Soil, 150: 193-201. Thomsen, I.K., 1993b. Turnover of ~SN-straw and NH4NO3 in a sandy loam: effect of previous straw disposal and fertilizer N dressings. Soil Biol. Biochem., 25:1561-1566. Thomsen, I.K., Hansen, J.F., Kjellerup, V. and Christensen, B.T., 1993. Effects of cropping system and rates of nitrogen in animal slurry and mineral fertilizer on nitrate leaching from a sandy loam. Soil Use Manage., 9: 53-58. Voroney, R.P., Paul, E.A. and Anderson, D.W., 1989. Decomposition of wheat straw and stabilization of microbial products. Can. J. Soil Sci., 69: 63-67. Wagger, M.G., Kissel, D.E. and Smith, S.J., 1985. Mineralization of nitrogen from nitrogen- 15 labelled crop residues under field conditions. Soil Sci. Soc. Am. J., 49: 12201226.