Unlike conventional cropping systems, which are characterised by targeted short-term fertility management, organic farming systems depend on long-term increase in soil fertility and promotion of soil biodiversity. This study sought to investigate long-term effects of organic matter inputs on various cropping systems in a 10-year-old experiment. Results show that in the long-term high C and N inputs enhance microbial activity. Microbial biomass N and the potential nitrification rate were higher in cropping systems based on green manure than in those reliant on inputs from animal manure and mineral fertilizer. Soil microbiological properties were affected by the individual crops in the rotation. The high microbial activity with increased organic matter inputs did not transform to enhanced crop productivity

Chirinda, Mr Ngonidzashe

Olesen, Professor Jørgen, E.

Porter, Professor John, R

English

Organic Eprints

16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008 Archived at http://orgprints.org/view/projects/conference.html Effects of organic matter input on soil microbial properties and crop yields in conventional and organic cropping systems Chirinda, N.1, Olesen, J.E.2 and Porter, J.R.3Key words: soil organic matter, crop yield, crop rotation, soil microbiology.  Abstract Unlike conventional cropping systems, which are characterised by targeted short-term fertility management, organic farming systems depend on long-term increase in soil fertility and promotion of soil biodiversity. This study sought to investigate long-term effects of organic matter inputs on various cropping systems in a 10-year-old experiment. Results show that in the long-term high C and N inputs enhance microbial activity. Microbial biomass N and the potential nitrification rate were higher in cropping systems based on green manure than in those reliant on inputs from animal manure and mineral fertilizer. Soil microbiological properties were affected by the individual crops in the rotation. The high microbial activity with increased organic matter inputs did not transform to enhanced crop productivity.  Introduction Crop production in organic farming systems relies to a large extent on soil fertility for nutrient supply. The soil fertility must be maintained via choice of crop rotation and (green) manuring practices. Fertility building by such means requires a long-term integrated approach, rather than the short-term and targeted solutions common in conventional agriculture (Watson et al., 2002). The fertility building in organic cropping systems has consequences for soil biological properties, which subsequently may influence N and C flows and emissions, including greenhouse gases (Robertson et al., 2000; Mäder et al., 2002). The changes in organic matter input may affect crop yields and soil properties differently in different systems depending on mineral nutrient supply to the crops. These effects can only be properly studied in long-term experiments, where the fertility effects of various cropping systems are reflected in changes in soil properties and in crop responses. In this paper we explore the effects of different organic matter inputs on crop yields and soil microbiological properties in a 10-year old cropping system experiment in Denmark. Materials and methods A crop rotation experiment was initiated in 1996/97 at three sites in Denmark (Olesen et al., 2000), but only data from the site at Foulum is used in this paper (Table 1). Foulum is located in Central Jutland on a loamy sand with an annual rainfall of 704                                                  1 University of Aarhus, Inst. of Agroecology and Environment, Box 50, 8830 Tjele, Denmark, E-Mail Ngonidzashe.Chirinda@agrsci.dk, Internet www.agrsci.dk2 University of Aarhus, Inst. of Agroecology and Environment, Box 50, 8830 Tjele, Denmark, E-Mail JorgenE.Olesen@agrsci.dk@agrsci.dk, Internet www.agrsci.dk3. University of Copenhagen, Faculty of Life Sciences,Hoejbakkegaard Alle 9, 2630 Taastrup Denmark.   Email: jrp@life.ku.dk    16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008 Archived at http://orgprints.org/view/projects/conference.html mm. During the period 1997 to 2004 the experimental factors were 1) proportion of N2-fixing crops in the crop rotation, 2) with (+CC) and without (-CC) catch crop, and 3) with (+M) and without (-M) animal manure. Two crop rotations (O2 and O4) with different proportions of cereals and nitrogen fixing crops in a four-year rotation were tested (Table 1). All crops in all rotations are represented every year in two replicates (blocks). The plots receiving manure were supplied with anaerobically stored slurry at rates where the NH4-N amount corresponded to 40% of the N demand of the specific rotation based on a Danish national standard (Plantedirektoratet, 1997). The grass-clover was used solely as a green manure crop, and the cuttings were left on the ground. All straw was left in the field. From 2005 the design was changed to include a conventional cropping system (C4) with a crop rotation similar to the O4 rotation (Table 1). Conventional treatments (C4) replaced the previous -CC/-M treatments in O2 and O4 such that O2/-CC/-M was converted to C4/+CC and O4/-CC/-M was converted to C4/-CC. The crops in C4 received mineral fertiliser at recommended rates. A mixture of legume and non-legumes were used for the catch crops in O2 and O4, whereas non-legumes were used in the C4 catch crop treatment. From 2001 the cuttings in grass-clover in O2/+M was no longer mulched, but removed from the field. Manure application is based on the principles of recirculation, where nutrients in the cuts from the grass-clover are processed by anaerobic digestion and redistributed to the row crop and cereals in the rotation. In O4/+M treatments the manure application is based on import from conventional farms. Weeds were controlled by mechanical means in O2 and O4, whereas pesticides were used at recommended rates in C4 to control weeds, pests and diseases. Table. 1: Structure of the crop rotations.   Crop rotation    O2     O4    C4 1st course 1997-2000 1 2 3 4   S. barley:ley  Grass-clover Winter wheatCC Pea/barleyCC Spring  oatCC Winter wheatCC Winter cerealCC,1 Pea/barleyCC  2nd course 2001-2004 1 2 3 4   S. barley:ley  Grass-clover Winter wheatCC Lupin/barleyCC Winter  wheatCC Spring oatCC S. barleyCC Lupin   3rd course 2005-2008 1 2 3 4   S. barley:ley  Grass-clover Potato Winter wheatCC,3 S.  barleyCC  Faba beanCC,2 Potato Winter wheatCC,3 S.  barleyCC  Faba beanCC,2 Potato Winter wheatCC,3CCCatch crop in the +CC-treatments, 1 Triticale in 1999 and 2000, 2 Pea/barley in 2005, 3 S. oats in 2005. Grain yields were measured at maturity using a combine harvester. Samples of total above-ground biomass in the grass-clover were taken in 1 m2 sample areas in each plot at each cut. To determine total crop production, samples of total above-ground biomass were taken in 1 m2 sample areas in each plot 1-2 weeks before maturity. Similar samples of total above-ground biomass were taken about 1 November to measure the above-ground biomass of catch crops and weeds. Total N in the grain and plant samples were determined on finely milled samples from each plot by the   16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008 Archived at http://orgprints.org/view/projects/conference.html Dumas method. Carbon content in plants was estimated under the assumption of 46% C content in plant DM biomass. Soil organic C and N were determined by dry combustion. Microbial biomass  was determined by the chloroform fumigation incubation technique (Joergensen and Brookes, 1990). Nitrification potential was assessed using the method described by Hart et al., (1994). Results There were higher C and N inputs from aboveground material in the organic compared to the conventional systems, in particular affected by the catch crop (CC) treatment (Table 2). The organic system O2/+CC received significant C and N inputs from grass-clover and O4/+CC from crop residues and catch crops. This was reflected in a higher soil organic C content in the organic compared to the conventional treatments (Table 3). Microbial biomass N and nitrifier activity was highest in the O2/+CC and lowest in the conventional system (Table 3). The microbial population and activity, which increased with organic inputs in plots that will have spring barley in 2008, but showed no clear trend in the winter wheat plots. Annual grain yields were consistently higher in conventional compared to organic systems (Table 4). Grain yields obtained in the O4/+CC were comparable with yields from the O2/+CC. The low yields obtained for spring oats in the conventional system in 2005 were due to crop lodging. Table 2. Annual C and N inputs in organic matter of manure and above-ground plant material (1997- 2006).  Source  C4/-CC  O4/-CC  O4/+CC  O2/+CC C  input  Manure  0.0    0.3   0.3   0.2   (Mg  DM/ha/yr)  Grass-clover  0.0    0.0   0.0   1.6     Crop  residues  2.1    2.4   2.9   2.4     Catch  crops  0.2    0.2   1.0   0.3     Total  2.3    2.9   4.2   4.5   N  inputs  Manure  0    18   18   15   (kg  N/ha/yr)  Grass-clover  0    0   0   95     Crop  residues  42    40   61   44     Catch  crops  10    9   58   16     Total  52    66   137   170    Table 3. Soil biological and chemical properties (+ S.E; n =2)  Soil Parameter  2008 crop                                       Treatment    C4  /-CC  O4/-CC  O4/+CC  O2/+CC Organic C (%)  S. barley  1.95  2.10  2.09  2.28   W.  wheat  1.91 2.29 2.00 2.39 Microbial biomass N (µg N / g soil) S.  barley 32.1(2.3) 36.3(2.3) 36.0(4.0) 47.2  (0.8)   W. wheat  27.2 (2.2)  32.7(1.3)  27.2*  29.2 (3.3) Potential Nitrification (nmol NO3 / g soil / h) S.  barley 10.6(0.3) 13.9(0.01)  15.5(1.6) 16.6(0.4)   W.  wheat 12.3(1.7) 16.3(1.9) 15.1(0.2) 17.9(0.2) Discussion   16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008 Archived at http://orgprints.org/view/projects/conference.html The results suggest that increased microbial activity follows increased annual C and N inputs in cropping systems. This finding agrees with Raupp (1995), who reported higher microbial biomass in organic compared to conventionally managed soils. Catch crops significantly increase soil organic matter levels (Olesen et al., 2007), thus microbial activity and grain yield were as expected lower in organic system without catch crops. In line with the observations made by Acosta-Martinez et al., (2004), microbiological parameters, unlike organic C, were effected by crop type. The lower microbial population after the potato crop that preceded winter wheat suggests that potatoes had a negative effect on soil rhizosphere microbial populations. The generally higher nitrifier activity could be due to high residual N as the 2007 potato crop was affected by disease. Increased organic matter inputs enhanced microbiological properties, but did not necessarily translate to improved crop productivity. This is inevitable in organic systems where plant nutrient demand is rarely in synchrony with nutrient availability (Watson et al., 2002). Table 4. Dry matter grain yields Mg DM ha-1 (+SE; n = 6) Crop  Year                                Treatment    C4/-CC  O4/-CC  O4/+CC  O2/+CC S.  oat  2005  4.12 5.11  5.42 5.27 W.  wheat  2006  7.05 5.19  6.08 6.16   2007  6.86 3.50  3.32 4.00 S.  barley  2005  6.25 4.92  5.19 4.86   2006  5.74 4.38  5.14 4.77   2007  4.64 3.13  4.53 4.51 Mean    5.78 (0.41)  4.37 (0.3)  4.95 (0.32  4.93 (0.25) References  Acosta-Martinez, V. Zobeck, T.M., Allen, V., 2004: Soil Microbial, chemical and Physical properties in continuous Cotton and Integrated Crop-livestock systems. Soil Sci. Soc. Am. J. 68:1875-1884. Hart, S. C., Stark, J.M., Davidson, E.A., Firestone, M.K. 1994. Nitrogen Mineralization, Immobilization and Nitrification. Methods of Soil Analysis, Part 2. Microbiological and Biochemical Properties-SSSA Book Series no. 5. Joergensen, R.G., Brookes, P.C. 1990. Ninhydrin-reactive N measurements of microbial biomass in 0.5 M K2SO4 soil extracts. Soil Biol. Biochem. 22:1167–1169.  Mäder, P., Fliessbach, A., Dubois, D., Gunst, L., Fried, P., Niggli, U. (2002): Soil fertility and biodiversity in organic farming. Science 296:1694-1697. Olesen, J.E., Askegaard, M., Rasmussen, I.A. (2000): Design of an Organic Farming Crop-Rotation Experiment. Acta Agric. Scand., Sect. B, Soil Plant Sci. 50:13-21. Olesen, J.E., Hansen, E.M., Askegaard, M., Rasmussen, I.A. (2007): The value of catch crops and organic manures for spring barley in organic arable farming. Field Crops Res. 100:168-178. Plantedirektoratet, (1997): Vejledning og skemaer, mark og gødningsplan, gødningsregnskab, grønne marker 1997/1998. Plantedirektoratet, Lyngby, Denmark. Raupp, J. (1995): Main effects of various organic and mineral fertilization on soil organic matter turnover and plant growth. Publications of the Institute for Biodynamic Research. Volume 5, Darmstadt. Robertson, G.P., Paul, E.A. and Harwood, R.R. (2000): Greenhouse gases in intensive agriculture: Contributions of individual gases to the radiative forcing of the atmosphere. Science 289:1922-1925. Watson, C.A., Atkinson, D., Gosling, P., Jackson, L.R. and Rayns, F.W. (2002): Managing soil fertility in organic farming systems. Soil Use Manage. 18:239-247.   

Effects of organic matter input on soil microbial properties and crop yields in conventional and organic cropping systems

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