Crop residue and fertilizer management effects on nutrient use and barley production

Transcription

1 Crop residue and fertilizer management effects on nutrient use and barley production Y. K. Soon Agriculture and Agri-Food Canada, Research Branch, P. O. Box 29, Beaverlodge, Alberta, Canada T0H 0C0. Received 2 July 1998, accepted 24 January Soon, Y. K Crop residue and fertilizer management effects on nutrient use and barley production. Can. J. Soil Sci. 79: Cereal straw has many potential on-farm and off-farm uses. If straw is to be removed from land, the practice should not adversely impact long-term crop production and soil quality. A 10-yr experiment was conducted on a Dark Grey Solod near Beaverlodge, Alberta (55 13 N, W) to determine the effects of fertilizer and straw management on the yield of, and nutrient (N and P) use by, continuous barley (Hordeum vulgare L.). Four straw management treatments: (i) straw removal; (ii) straw ploughed in; (iii) straw disked in; and (iv) straw disked in plus a red clover (Trifoleum pratense L.) green manure disked in every fifth year, were superimposed on four fertilizer treatments. The fertilizer treatments were application of N and P: (i) banded at soiltest recommended rates (ST,b); (ii) broadcast and incorporated at soil-test recommended rates (ST,bi); (iii) banded at soil-test rates of N+ 25 kg ha 1 and P+ 10 kg ha 1 (ST+,b); and (iv) as in (iii) but broadcast-applied and incorporated (ST+,bi). The straw ploughed-in treatment tended to produce lower annual barley yield and N uptake (by 9 and 13%, respectively) than the other three residue treatments. Barley yield and utilization of N and P were unaffected by straw removal as compared to disking-in straw. Barley yield and N uptake were higher (by 12 and 17%, respectively) with N and P application at the higher rate. At the recommended rate, broadcast-and-incorporated application of fertilizers resulted in lower yields and nutrient use than banded-in application. Treatment effects on P uptake tended to be small. The green-manured treatment used less fertilizer N, resulted in less total barley grain production, and did not increase the amount of crop residues incorporated. It is concluded that grain yield and nutrient (N and P) use of a continuous barley cropping system, fertilized at recommended rates of N and P, were unaffected by straw removal. Key words: Crop residue management, continuous barley production, fertilizer N and P Soon, Y. K Effets de la conduite des restes de culture et de la fumure minérale sur l utilisation et la valorisation des éléments nutritifs par une culture d orge. Can. J. Soil Sci. 79: La paille des céréales offre de nombreux usages tant à la ferme qu à l extérieur. Si elle doit être enlevée du terrain, la pratique n en devrait pas pour autant compromettre la productivité à terme de la terre ni la qualité du sol. Une expérience de 10 ans a été réalisée aux environs de Beaverlodge en Alberta (55 13 N, O) dans un solod gris foncé pour observer les effets de la conduite de la fumure minérale et des restes de culture sur le rendement de l orge (Hordeum vulgare L.) cultivé en continu et sur l utilisation des nutriments (N et P) par la culture. Quatre modes de gestion de la paille étaient comparés: i) enlevée du terrain, ii) enfouie à la charrue, iii) enfouie superficiellement à la déchaumeuse et iv) comme en iii avec trèfle rouge (Trifolium pratense L.) en sous-semis la quatrième année de la rotation puis enfoui avec l orge comme engrais vert tous à la cinquieme. Ces traitements étaient surimposés à quatre modalités d épandage des engrais (N et P): i) en bande aux doses recommandées selon l analyse du sol (b, a.s.), ii) en pleine surface avec incorporation aux doses recommandées selon l analyse du sol (p.s.i., a.s.), iii) en bande aux doses a.s. plus 25 kg N et 10 kg P ha 1 (b. a.s.+) et iv), comme en iii mais épandage en nappe avec incorporation (p.s.i., a.s.+). L enfouissement de la paille à la charrue entraînait un rendement grainier et une absorption de N annuels par l orge de 9 et 13 % respectivement inférieurs à ceux observés dans les 3 autres traitements de la paille. Il n y avait par ailleurs pas de différences à cet égard entre l enlèvement de la paille et le déchaumage. Le rendement de l orge et l exportation de N étaient, respectivement, de 12 et 17 % plus importants à la dose supérieure de N et P. À la dose recommandée l épandage en pleine surface avec incorporation des engrais se soldait par des rendements grainiers et par des exportations d éléments nutritifs inférieurs à ceux obtenus avec l épandage en bande. Les effets des traitements sur l absorption de P par la culture étaient en général de peu d importance. Le traitement avec engrais vert donnait lieu à une moindre utilisation du N de fumure et, par conséquent, à une moindre production grainière totale de l orge, sans pour autant augmenter la quantité des résidus enfouis. Il découle de nos observations que l enlèvement de la paille n a pas eu d effets négatifs sur le rendement grainier ni sur l utilisation des éléments nutritifs N et P dans un assolement d orge en continu, fertilisé aux doses N et P recommandées. Mots clés: Gestion des restes de culture, cultures de l orge en continu, engrais chimiques N et P Crop residues typically comprise 50% or more of net crop production. As a resource, crop residues such as straw have traditionally been used as materials for home construction, fuel, bedding, feed for farm animals, and as a source of nutrient and organic matter when returned to the soil after grain harvest (Unger 1994). The demand for wood fibre is increasing while the need to protect the dwindling forests and associated habitats is also being acknowledged. The 389 ability of cereal straw to partially meet this demand has been recently recognized (Øskov 1985; Unger 1994). Presently, several new industrial uses for straw are being explored and promoted (Alberta Agriculture, Food and Rural Development 1996; McClintic 1997; Øskov 1985). Stumborg et al. (1996) concluded that economic returns would make crop residue export an attractive diversification option for farms in the moister parts of the Canadian prairie.

2 390 CANADIAN JOURNAL OF SOIL SCIENCE It is estimated that after soil conservation and livestock requirements have been satisfied, 1 Tg of wheat straw would be available for alternative uses in an average year in Alberta (Alberta Agriculture, Food and Rural Development 1996). However, before the export of straw from farms becomes a common practice, it must be demonstrated to have no long-term effects on soil productivity and quality and to be economically feasible. It has been shown for the Black Chernozemic soils of the Canadian prairie that there was no long-term effect on crop yield when barley straw was removed by spring burn (Nuttal et al. 1986) or when wheat straw as removed by baling (Campbell et al. 1991) as compared with incorporating or retaining chopped straw. Moreover, these workers also demonstrated that straw removal had no measureable effect on organic carbon or total nitrogen in the soil when adequate fertilizers were used. However, straw incorporation by ploughing decreased soil organic carbon and total nitrogen, and straw incorporation by tillage in general increased the erosive (<0.83 mm) fraction of soil compared with no-till treatments (Nuttall et al. 1986). The long-term effects of straw and fertilizer management on crop production and soil quality of the grey soils of the Canadian prairie have not been well-documented. Nyborg et al. (1994) showed that removal of barley straw had no measurable effect on the average yield of barley after 11 yr among systems with similar tillage. They reported, however, that tillage and fertilizer management affected barley yields: conventional tillage increased barley yields compared with no-till, and application of 56 kg N ha 1 increased yields compared with no-n treatment, regardless of residue treatments. Another impetus for removal (partial or full) of straw from grey soil cropping systems is the large amount of residues produced, especially from barley, which can be troublesome by reducing soil temperatures and delaying spring seeding. Because the grey soils have lower organic matter content than the Black Chernozemic soils, it is particularly urgent that long-term effects of straw removal be quantified and disseminated to producers. Therefore, a study was initiated in 1985 on a Dark Grey soil to determine the long-term effects of residue removal or incorporation by various methods, and their interaction with soil fertility levels, on nutrient use, sustainability of barley yield and soil quality. The soil quality aspect has been reported previously (Soon 1998) in which it was shown that barley straw removal did not adversely affect soil organic carbon and some related nutrient pools and properties. The effects of 10 yr of residue and fertilizer management on nutrient use and barley yields are reported here. MATERIALS AND METHODS A red fescue (Festuca rubra L.) sward at the experimental site, approximately 8 km east of Beaverlodge, Alberta (55 13 N, W) was ploughed up in the summer of 1984 in preparation for the study. The predominant soil type is a Dark Grey Solod (Esher silty clay loam). The experiment was a 4 4 strip plot (Gomez and Gomez 1984) or split-block design (Little and Hill 1978), laid out in a randomized block arrangement with three blocks or replications. Four crop residue treatments were imposed on each of four fertilizer management treatments. Each plot was 7.62 m by 4.57 m. Barley (Hordeum vulgare L.) was grown every year except as noted below. The crop residue treatments were (i) straw removed (baled), (ii) straw ploughed in (to 14 cm depth), (iii) straw disked in (10 to 12 cm depth), and (iv) straw disked in with a red clover (Trifolium pratense L.) grown as a companion crop in the fourth year and disked in as green manure in the fifth year. Thus, treatment (iv) was repeated twice in the 10-yr study. Barley residues were incorporated, usually in mid-october. Fertilizer treatments consisted of spring application of N and P fertilizers: (i) banded at soil-test recommended rates (ST,b); (ii) broadcast and incorporated at soil-test recommended rates (ST,bi); (iii) banded at soil-test rates of N + 25 kg ha 1 and of P + 10 kg ha 1 (ST+,b); and (iv) as in (iii) but broadcast-applied and incorporated (ST+,bi). The fertilizer treatments were randomly assigned to each block in strips across the residue treatments. Fertilizer application rates for each of the 16 treatments were based on the means of their soil-test results. Fertilizer N rates were calculated from a target of 95 kg N ha 1 less nitrate-n in top 60 cm of soil (Alberta Agriculture 1988). The P fertilizer used was or , and additional N was applied as urea fertilizer. Soil samples were taken in late September or early October for soil test analysis and fertilizers were applied at seeding. Banded fertilizers were placed approximately 4 cm beside and below the seed. In 1985, the pretreatment year, all plots received the same treatment (e.g. 100 kg N ha 1 and 21 kg P ha 1 broadcastapplied and incorporated prior to seeding barley) until after harvest when the appropriate crop residue treatments were applied. Otal barley was grown 1985 through 1987, and Heartland barley, 1988 through 1996, except 1994, when Stacey barley was grown due to a shortage of Heartland barley. Seeding rate was 94 kg ha 1. Seed rows were 23 cm apart. In spring, the plots were tilled once or twice with tandem disks, followed by harrow and packer. In the fourth year of the cropping cycle, crop residue treatment (iv) was seeded to barley at half the normal seeding rate, i.e. at 47 kg ha 1, and red clover at 10 kg ha 1. The red clover was incorporated the following year by disking at the bloom stage. The crop rotation was repeated in The treatments were imposed on the same set of plots from 1985 through Weeds were controlled chemically as required. Approximately 1 wk before harvesting, a 60-cm strip of barley was removed from the four sides of each plot. At maturity, barley plants were swathed 7 to 8 cm above ground level and grain yields taken with a plot combine. Straw dry matter was estimated as the difference between total crop dry matter less grain yield from four 1-m rows cut 2 cm above ground level before swathing. Red clover samples were taken from a 1-m 2 area at the time of incorporation in 1990 for dry matter and N determination. Barley plant samples were taken from four 1-m rows in 1991 to 1995 for nutrient analysis. Samples were taken at dough stage in 1991 to 1993, and at maturity in 1994 and 1995, dried (65 C), ground and micro-kjeldahl digested

3 SOON STRAW AND FERTILIZER EFFECTS ON BARLEY PRODUCTION 391 Table 1. Grain yield of barley, , as affected by residue and fertilizer management z Year Management Mg ha 1 Total (i) Removed (ii) Ploughed in (iii) Disked in (iv) Disked in + GM v y NC x y NC x 23.7 SE (6 df) ND w * Fertilizer u (i) ST,b (ii) ST,bi (iii) ST+,b (iv) ST+,bi SE (6 df) 0.26* * ND w * Year mean z Yields adjusted for 15% moisture. y Barley was underseeded to red clover. x No crop yield due to red clover green manure. w Standard error not determined because of uneven establishment and growth. v Red clover green manure every fifth year. u ST and ST+ denote N and P applied at, and at 25 and 10 kg ha 1 above recommended rates, respectively; b and bi denote band and broadcast-incorporate *Denotes that treatment differences were significant at P = using Se + Na 2 SO 4, and analysed for N, P and K (Soon and Kalra 1995). The experimental data for each year were analysed by the General Linear Model using SAS programs (SAS Institute, Inc. 1990). Treatment effects and interactions were considered significant at P RESULTS AND DISCUSSION Grain Yield and Straw Production There were no obvious problems with crop disease in spite of the monoculture. There were few significant effects of crop residue or fertilizer management on grain yield of barley (Table 1). Yields were low with Otal barley ( ), an older, low-yield cultivar, typically less than 2 Mg ha 1. Grain yield was also low in 1990 becuase of excessive rainfall and low temperatures in May and June. The residue ploughed-in treatment tended to yield less than the disked-in treatment (difference was significant only in 1995). The reason for this may be the deterioration in soil quality with this tillage treatment as measured by soil organic carbon, total nitrogen and microbial biomass (Soon 1998). Nyborg et al. (1994) reported that barley yields at two sites near Edmonton, Alberta, were similar over an 11- yr period whether straw was removed or retained. Application of N and P fertilizers at higher than recommended rates regardless of application method tended to produce the highest barley grain yields. Ten-year cumulative yield was lowest with N and P broadcast-applied and incorporated at recommended rates. This may be related to greater immobilization of fertilizer nutrients with broadcastand-incorporate application as compared with band application (Malhi et al. 1989). There was no interaction between Table 2. Cumulative yield of barley straw (and red clover dry matter at disk-in z ) between and as affected by residue and fertilizer management Yearly mean Management Mg ha 1 (i) Removed (ii) Ploughed in (iii) Disked in (iv) Disked in + GM x 19.9(3.9) 20.2( y ) 4.0 Fertilizer w (i) ST,b 20.6(2.5) (ii) ST,bi 20.3(5.3) (iii) ST+,b 23.4(3.6) (iv) ST+,bi 24.4(4.3) z Red clover dry matter disked-in is shown in parenthesis. y Red clover plots were mistakenly seeded with barley, and fallowed after desiccation with glyphosate in late July; dry matter was not determined. x Red clover green manure every fifth year. w ST and ST+ denote N and P applied at, and at 25 and 10 kg ha 1 above recommended rates, respectively; b and bi denote band and broadcastincorporate residue and fertilizer management effects. The mean harvest index of the barley was The residue ploughed-in treatment also produced the lowest amount of straw per year (Table 2). The green-manured treatment did not increase the amount of crop residues returned to the soil. The average amount of red clover above-ground dry matter incorporated in the summer of 1990 was 3.93 (SE = 0.37) Mg ha 1. The amount of nitrogen incorporated with the above-ground portion of the green manure was 120 (SE = 17) kg ha 1. These are typical values for red clover green manure in the region (Rice 1980). In

4 392 CANADIAN JOURNAL OF SOIL SCIENCE Table 3. Nitrogen uptake by barley in 1991 to 1995 as affected by crop residue and fertilizer management 1991 z 1992 z 1993 z 1994 y 1995 y Mean Management kg N ha 1 (i) Removed (60) 89(49) 86 (ii) Ploughed in (45) 73(38) 75 (iii) Disked in (61) 100(61) 93 (iv) Disked in + GM x (42) 81 SE (6 df) * ND w 20(12) 14(8)* Fertilizer v (i) ST,b (49) 79(45) 82 (ii) ST,bi (41) 76(39) 69 (iii) ST+,b (59) 84(51) 90 (iv) ST+,bi (59) 111(62) 93 SE (6 df) 10 8* ND w 20(11) 13(9)* Year mean (52) 88(49) z Shoot samples at dough stage. y Maturity samples, grain N uptake in parentheses. x Red clover green manure every fifth year. w No standard error estimate made due to patchy growth. v ST and ST+ denote N and P applied at, and at 25 and 10 kg ha 1 above recommended rates, respectively; b and bi denote band and broadcast-incorporate *Denotes that treatment differences were significant at P = Table 4. Phosphorus uptake by barley in 1991 to 1995 as affected by crop residue and fertilizer management 1991 z 1992 z 1993 z 1994 y 1995 y Mean Management kg P ha 1 (i) Removed (9.6) 13.4(9.7) 10.6 (ii) Ploughed in (7.7) 11.1(7.5) 10.0 (iii) Disked in (10.2) 15.5(12.0) 11.3 (iv) Disked in + GM x (7.7) 9.7 SE (6 df) ND w 2.0(1.9) 2.4(1.7)* v Fertilizer v (i) ST,b (9.1) 13.8(10.1) 11.0 (ii) ST,bi (6.6) 10.3(7.0) 8.4 (iii) ST+,b (9.9) 14.0(10.5) 11.2 (iv) ST+,bi (9.5) 15.2(11.2) 11.5 SE (6 df) ND w 1.9(1.5)* 1.7(1.5)* Year mean (8.8) 13.3(9.7) z Shoot samples at dough stage. y Maturity samples, grain P uptake in parentheses. x Red clover green manure every fifth year. w No standard error estimate made due to patchy growth. v ST and ST+ denote N and P applied at, and at 25 and 10 kg ha 1 above recommended rates, respectively; b and bi denote band and broadcast-incorporate *Denotes that treatment differences were significant at P = , the red clover plots were seeded to barley in error: plant cover in those plots was chemically desiccated with glyphosate in July and the dried residues incorporated in October. Dry matter accumulation at that time was not measured. Higher application rates of N and P than recommended had a similar effect on straw production as grain yield (13% increase over 10 yr for both as compared with recommended rates). Assuming that 25% of the barley residues remains chaff and stubble, approximately 3.5 t ha 1 of straw would be available for baling each year. The straw contained 10, 1.07 and 18.3 g kg 1 of N, P and K, respectively. The results of this study on a Dark Grey Solod suggest that providing fertilization was adequate (i.e., at recommended levels), straw removal over a 10-yr period had no measurable impact on grain yield of barley. The results concur with those of Nuttall et al. (1986) in showing that grain yield was lowest with plough incorporation of crop residues. Nutrient Use and Uptake Nitrogen uptake tended to be lower with residues ploughedin compared to the disked-in treatment (Table 3). Straw removal did not affect N uptake significantly. The higher fertility treatments also tended to increase N uptake (by an average of 16 kg ha 1 in 1994 and 1995 as well as over the 5-yr period ). Nitrogen and P broadcast-applied and incorporated (at recommended rates) consistently

5 SOON STRAW AND FERTILIZER EFFECTS ON BARLEY PRODUCTION 393 Table 5. Average annual N and P fertilizer application rates for crop residue and fertilizer treatments during two cropping cycles Fertilizer treatment z Nitrogen applied (kg ha 1 yr 1 ) Phosphorus applied (kg ha 1 yr 1 ) Crop residue N N+ N N+ P P+ P P+ (i) Removed (ii) Ploughed in (iii) Disked in (iv) Disked in + GM y Mean z N and P are the means for the two ST (recommended rate) treatments, and N+ and P+ for the two ST+ (above recommended rate) treatments. The cropping cycles are and y Red clover green manure every fifth year. resulted in lower N and P uptake than the equivalent band application method (Tables 3 and 4). This may be due to greater immobilization of fertilizer nutrients with the broadcast-and-incorporate application method (Malhi et al. 1989). The observed differences in N and P uptake were only partly related to differences in grain and dry matter production induced by the fertility treatments; there was a concentration effect as well that was associated with higher fertilizer rates (nutrient concentration data not shown). Variations in P uptake due to residue management effects were relatively small (Table 4). The higher fertilizer application rate did not result in 25 kg more N and 10 kg more P applied per hectare per year over the study period than the recommended rate, because a gradual build up of soil fertility (i.e., higher soil-test values) resulted in lower application rates (Table 5). Fertilizer N and P use, especially the latter, was lower in the second cropping cycle than the first at both recommended and aboverecommended rates. The build-up in soil fertility was especially evident for phosphorus as shown by the increase in extractable soil P with time (Soon 1998), and by 1995 most plots were not requiring P fertilizer addition. During the second cropping cycle, soil nitrate to 90-cm depth in the autumn averaged 12 kg N ha 1 higher (range 3 to 20 kg ha 1 ) in the ST+ treatments compared with the ST treatments (Soon 1998). The residue ploughed-in treatment had the highest fertilizer N requirement as indicated by soil test results (Table 5), but resulted in the lowest N uptake (Table 3). This inefficient use of N may be associated with a larger loss from the soil plant system. The straw disked-in and straw-removed treatments had nearly similar N requirements. Koenig and Cochran (1994) showed that with a C:N ratio of almost 40:1, barley residues contributed very little N to soil N cycling, either in the winter or the following growing season. Mineralized N was thought to be immobilized rapidly. This would explain to some extent the similar N requirement and uptake between straw-removed and strawdisked-in treatments. The red clover green manure treatment substantially reduced fertilizer N application. Zero to 20 kg ha 1 of fertilizer N was applied to barley underseeded with red clover, and none was applied to the established red clover, or to the barley (ST treatments only) following red clover incorporation, i.e., little N was applied for 3-yr of each cropping cycle. At recommended rate for N (i.e. ST treatments), the green-manured treatment used 355 kg ha 1 less fertilizer N and produced 6.4 Mg ha 1 less grain that the straw disked-in treatment over the 10-yr study period. At a recent unit (kg 1 ) price of 9.1 cents for feed barley, and 61 cents and $2.02, respectively, for fertilizer N (as urea) and P, the extra yield (220 kg ha 1 yr 1 ) from banding in N and P at above recommended rates (ST+,b treatment in Table 1) is probably not enough to justify the additional risk incurred (extra income of $20.00 vs. extra cost of $18.06 per ha). GENERAL DISCUSSION AND CONCLUSION Producers contemplating selling straw have to deal with four issues. Two of these are contractual issues (Alberta Agriculture, Food and Rural Development 1996) and will not be addressed here. The first issue concerns whether partial or full removal of straw would impact soil quality and productivity. This report showed that provided fertilization was adequate productivity as measured by 10-yr barley yield was unaffected by straw removal as compared with incorporation of straw by disking. Incorporation of straw by ploughing tended to reduce barley yield and N and P utilization. A previous report of this study (Soon 1998) also showed that straw removal did not adversely affect soil quality attributes such as organic carbon and total nitrogen content, soil microbial biomass C and N, and soil carbohydrate content. Presumably, in spite of straw removal, sufficient residues were recycled in the study are as stubble, roots and rhizodeposits to meet the energy requirements of soil biota. Straw removal did not affect N and P requirement and utilization as compared to disking in the straw. It is concluded that the first issue is not an impediment. The second issue concerns the compensation the producer should receive for the straw. At the very minimum, the price of straw should include the replacement value of nutrients exported in straw plus the cost of baling and loading. The replacement cost of NPK nutrients contained in straw removed in the current study was $11.80 Mg 1 of straw. Obviously, the replacement value will vary to some extent depending on the nutrient content. Thus, using typical NPKS content, the nutrient replacement value ranged from $13 to $15 Mg 1 at 1996 prices (Alberta Agriculture, Food and Rural Development 1996). The cost of baling and load-

6 394 CANADIAN JOURNAL OF SOIL SCIENCE ing has been estimated at $14.29 Mg 1 (Stumborg et al. 1996) and $20 Mg 1 (Alberta Agriculture, Food and Rural Development 1996). Therefore, total compensation at farm gate would range from $26 to $35 Mg 1. According to Wong et al. (1993), cereal straw can be contracted for agripulp production at $40 Mg 1 FOB. Thus, as Stumborg et al. (1996) showed, there is economic opportunity for producers in the Grey and Black soil zones to export straw. ACKNOWLEDGEMENTS I thank Larry Kerr for taking care of the field work associated with this long term project and M. Qureshi for technical assistance. Alberta Agriculture Soil test recommendations for Alberta. Alberta Agriculture, Edmonton, AB. Alberta Agriculture, Food and Rural Development Alternative straw use industry. Agdex 110/ Alberta Agriculture, Food and Rural Development, Edmonton, AB. Campbell, C. A., Lafond, G. P., Zentner, R. P. and Biederbeck, V. O Influence of fertilizer and straw baling on soil organic matter in a thin Black Chernozem in western Canada. Soil Biol. Biochem. 23: Gomez, K. A. and Gomez, A. A Statistical procedures for agricultural research. 2nd ed. J. Wiley & Sons, New York, NY. Koenig, R. T. and Cochran, V. L Decomposition and nitrogen mineralization from legume and non-legume crop residues in a subarctic agricultural soil. Biol. Fertil. Soils 17: Little, T. M. and Hill, F. J Agricultural experimentation: design and analysis. J. Wiley & Sons, New York, NY. Malhi, S. S., Nyborg, M. and Solbert, E. D Recovery of 15 N-labelled urea as influenced by straw addition and method of placement. Can. J. Soil Sci. 69: McClintic, C Molding new markets for straw. The Furrow, Nov. 1997, pp Nuttall, W. F., Bowren, K. E. and Campbell, C. A Crop residue management practices, and N and P fertilizer effects on crop response and on some physical and chemical properties of a Black Chernozem over 25 years in a continuous wheat rotation. Can. J. Soil Sci. 66: Nyborg, M., Solberg, E. D., Malhi, S. S., Izaurralde, R. C. and Molina-Ayala, M Influence of long-term tillage, straw and N fertilizer on barley yield and on N uptake. Pages in H. E. Jensen, P. Schonning, S. A. Mikkelsen, and K. B. Madsen, eds. Soil tillage for crop production and protection of the environment. Proc. 13th Intern. Conf. Int. Soil Tillage Research Organization, Vol July 1994, Aalborg, Denmark. Øskov, B Cereals and the road to a rational agriculture. New Scientist, 12, Sept. 1985, pp Rice, W. A Seasonal patterns of nitrogen fixation and dry matter production by clovers grown in the Peace River region. Can. J. Plant Sci. 60: SAS Institute, Inc SAS/STAT user s guide. Version 6, 4th ed. SAS Institute, Inc., Cary, NC. Soon, Y. K Crop residue and fertilizer management effects on some biological and chemical properties of a Dark Grey Solod. Can. J. Soil Sci. 78: Soon, Y. K. and Kalra, Y. P A comparison of plant tissue digestion methods for nitrogen and phosphorus analysis. Can. J. Soil Sci. 75: Stumborg, M., Townley-Smith, L. and Coxworth, E Sustainability and economic issues for cereal crop residue export. Can. J. Plant Sci. 76: Unger, P. W. (Ed) Managing agricultural residues. Lewis Publ., Boca Raton, FL. Wong, A., Krzywanski, R. and Chui, C Agriculture-based pulp as secondary fibres. Tappi Pulping Conference, November 1993, Atlanta, GA.

7 This article has been cited by: 1. Neil C. Hansen, Brett L. Allen, Saseendran Anapalli, Robert E. Blackshaw, Drew J. Lyon, Stephen Machado. Dryland Agriculture in North America [Crossref] 2. S.S. Malhi, M. Nyborg, E.D. Solberg, M.F. Dyck, D. Puurveen Improving crop yield and N uptake with long-term straw retention in two contrasting soil types. Field Crops Research 124:3, [Crossref]