The challenge Planetary boundaries

Transcription

1 Erik Steen Jensen and Henrik Hauggaard-Nielsen Intercropping: crop management for reduced inputs of reactive nitrogen and related GHG emissions? - prospects for a sustainable and climate smart agriculture The Second Climate Smart Agriculture Global Science Conference UC Davis and World Bank, March 20-22, 2013 The challenge Planetary boundaries Rockström, J. et al A safe operating space for humanity. Nature 461,

2 Global reactive N input from fertilizer and BNF (2008) Reactive N input (million t/yr) N-fertilizer 25% BNF 25% Galloway, J. N. et al Transformation of the N cycle. Recent trends, questions and potential solutions. Science 320, 889; Herridge, D.F, Peoples, M.B, and Boddey, R.M Global inputs of biological N2 fixation in agricultural systems. Plant and Soil, 311, 1-18.? 2

3 BNF = Reactive N with less climate impact? Reduced fossil energy use in legume-based systems compared to fertilizer based Enhanced carbon sequestration, due to legumes Lower N 2 O emission associated with N-supply during the growth season compared to N-fertilized crops Cropping system Variation (kg N2O- N/ha) Average (kg N2O-N/ha) [number of sites] N-fertilized crops [71] Legume crops [67] Bare soil [33] Jensen ES, Peoples MB, Boddey RM, Gresshoff PM, Hauggaard Nielsen H, Alves BJR and Morrison MJ Legumes for mitigation of climate change and the provision of feedstock for biofuels and biorefineries a review. Agronomy for Sustainable Development. 32, Optimal synchronization and 100% use efficiency, but yield variability 3

4 Soil N mineralization Has cheap N-fertilizer and BNF technology diverted us from focusing sufficiently on efficient use of the ecosystem service from soil N mineralization? Understanding the variability in time and space (patchiness) of the soil available N pool and its link to C dynamics and crop N supply is still a challenge.? Nodulated legumes need only a limited amount of soil N Is it waste of mineral soil N to grow a legume as a sole crop? Landscape controls of soil N availability and dinitrogen fixation Stevenson, F.C., Knight, J.D and van Kessel, C Dinitrogen fixation in pea Controls at the landscape and microscale. Soil Sci. Soc. Am J. 59,

5 Towards reducing reactive N inputs and associated GHG emissions Reduced reactive N inputs require greater and safe recycling of N from urban areas to agricultural land. Improved cycling on- and between farms e.g. between arable-livestock farms. Reactive N with less global warming impact Increased use efficiency of soil and fertilizer N sources: breeding for low inputs, synchronization of demand and availability and diversification of cropping systems in time and space. Eco-functional intensification Activating more knowledge. Intensifying the beneficial effects of ecosystem services, including biodiversity and soil fertility. Uses the self-regulating mechanisms of organisms and of biological or organizational systems. Closes materials cycles to minimize losses. It searches for the best match between environmental variation and the genetic variability of plants and crops. EU Technology Platform Organics

6 Intercropping (IC): an example of eco-functional intensification IC widespread globally in small scale farming systems Increased yield per unit area Reduced risk and improved stability, due to agrobiodiversity effects on weeds, diseases and pests Improved nutrient and water use A variety of systems adapted to local conditions Diversity in food supply Multiple Cropping ASA special publication (Eds. Papendick, Sanchez and Triplett) ASA, CSSA, SSSA. A role for intercropping of cereal and legumes in a global north context of climate smart agriculture? Enhanced use efficiency of soil mineral N sources via: competitive interactions and self-regulation? Complementarity of legume N 2 fixation 6

7 Sharing (competition for) of mineral N sources NO 3 NH 4 Sharing of soil N in intercrops Sole intercrops, Kg fertilizer N/ha 15N labeling NA- natural abundance Cereal SC Legume SC IC Reference Soil and Fertilizer Kg N/ha Soil and Fertilizer Kg N/ha N2 fixation Kg N/ha Soil and Fertilizer (Cereal/legume total) kg N/ha N2 fixation Kg N/ha Wheat-fababean, 50, 15N / Jensen 1986 Maize-cowpea, 25, 15N / Ofori et al 1987 Barley-pea, 10, 15N / Izaurralde et al 1992 Barley-pea, 50, 15N / Jensen 1996 Barley-pea, 50, 15N, M 98/ Jensen 1997 D 112/ Dp114/ Wheat-pea, 40, 15N / Ghaley et al 2005 Barley-pea, 40, 15N B / Andersen et al Rape-pea, 40, 15N R 75 61/ Oat-pea, 0, NA / Neumann et al 2006 Barley-pea A, 0, NA / Hauggaard- Barley-pea B, 0, NA / Nielsen et al Barley-faba, 0, NA / (sandy Barley-lupin, 0, NA / loam) Mean of experiments / Means of three years field experiments 7

8 The INTERCROP Project Soil N use in European pea-barley IC LER AB = N PB N PP + N BP N BB Pea100%Barley50% Pea50%Barley50% Hauggaard Nielsen, H. et al Pea barley intercropping for efficient symbiotic N 2 fixation, soil N acquisition and other nutrients in European organic cropping systems. Field Crops Research 113, Self-regulation in intercrop N acquisition 300 Crop N accumulation (kg N/ha) % barley 80% barley Pea N Barley N 50% barley 20% barley 100% pea N-fertilizer (kg N/ha) Jensen, E.S. (in prep). Means of three years experiments on a sandy loam soil. Replacement design 8

9 Soil and fertilizer accumulation of barley plants as influenced by N fertilizer and crop design 160 mg soil and fertilizer N/barley plant % barley 80% barley 50% barley 20% barley N-fertilizer (kg N/ha) Jensen, E.S. (In prep) Means of three years experiments on a sandy loam soil. Replacement design Facilitation of N 2 fixation? NO 3 NH 4 9

10 The INTERCROP Project %Ndfa and relative N 2 fixation in pea Hauggaard-Nielsen, H., et al Pea-barley intercropping for efficient symbiotic N 2 -fixation, soil N acquisition and other nutrients in European organic cropping systems. Field Crops Research 113, Grain yield (Mt/ha) Grain yield of SC and IC of pea an barley as influenced by N-fertilizer and IC design SC barley Pea Barley 80% barley 50% barley 20% barley SC pea LER N-fertilizer (kg N/ha) Jensen, E.S. (in prep). Means of three years experiments on a sandy loam soil. Replacement design 10

11 Additional services from cereallegume intercrops More balanced C/N ratio of residues than sole crop cereals for SOM building (Jensen et al., 2012) and for reduced N- leaching (Hauggaard-Nielsen et al. 2003; Nie et al. 2012). Reduced emission of N 2 O (Dyer et al. 2012) Improved use of P, K an S (Hauggaard-Nielsen et al, 2009). Reduced weed infestation compared to SC legumes (Corre-Hellou et al. 2011). Disease and pest control (Hauggaard-Nielsen et al. 2008; Altieri,1999) Higher protein concentration of intercropped cereal (Jensen, 1996) Conclusions Non-proportional sharing of soil N ensures sufficient N supply for IC cereal plants, A pea-barley IC may self-regulate to soil N availability at the landscape level, due to competitive interactions between species. The cereal facilitate BNF by competing for soil N, but competitive interactions for other factors may limit BNF. Facilitation by legume N transfer is modest in annual intercrops. Similar grain yields, but significantly greater protein yields may be obtained with pea-barley ICs without N-fertilizer as compared to N-fertilized barley SC. The IC yield stability is greater than of SC pea. Intercropping seems as a valuable methods for efficiency and complementarity in soil N use and BNF with reduced climate impact. Intercropping cereals and grain legumes may be a tool for reducing the input of new reactive N compared to sole crops at similar yield levels 11

12 Recommendations for future sustainable and climate smart agriculture Despite its many potential advantages and occurrence in agriculture (especially in subsistence farming) intercropping has received relative little attention by mainstream agronomic research (Francis, 1987). The complexity of intercrop/multispecies systems requires an agroecological approach with agronomy, ecology, social sciences, simulation modeling as some of the key competences, The importance of IC for small scale farmers and its potential for reducing reactive N inputs and mitigation of N-related GHG emission point to the requirement for giving the area the share of research attention that it warrants. Priority research questions: Integration of ICs in rotations Developing cultivars for intercropping Technology for crop management and harvest Barriers to IC in the food system. Andersen/Busse Nielsen Thank you 12

13 Climate-smart agriculture, an agriculture that sustainably increases productivity, resilience (adaptation), reduces/removes greenhouse gases (mitigation), while enhancing the achievement of national food security and development goals. FAO 2012 Climate-smart agriculture. Protein yield of SC and IC of pea an barley as influenced by N-fertilizer and IC design Pea Barley SC pea Protein yield (kg/ha) SC barley 80% barley 50% barley 20% barley N-fertilizer (kg N/ha) Jensen, E.S. (in prep). Means of three years experiments on a sandy loam soil. Replacement design 13

14 Coefficient of variation (%) Yield variability of sole and intercrops of pea and barley SC barley 80% barley 50% barley 20% barley SC pea N-fertilizer (kg N/ha) Jensen, E.S. (in prep). Means of three years experiments on a sandy loam soil. Replacement design Main messages Intercropping of a cereal and grain legume is an example of eco-functional intensification to obtain: enhanced efficiency in use of soil N compared to sole cropping complementary biological N 2 fixation with lower emission of GHGs, on the same piece of land, reduced input of reactive N with lower climate impact, compared to sole crops, similar grain yields of ICs without N-fertilizer as the sole crop cereal fertilized with N, but with greater protein yields of the ICs, and greater yield stability compared to the sole crop grain legume 14

15 Intercropping The simultaneous cultivation of several species within a field Net Transfer of N from pea to barley? Transfer of N assimilated by grain legumes to intercropped cereals occur in small amounts, but have only significance for barley at very low levels of soil N availability. Arbuscular mycorrhizano mediate 3 reverse N transfer, but enhances only the contribution NH 4 to associated plant N, if the root system is decaying. mycorrhiza Jensen, E.S Barley uptake of N deposited in the rhizosphere of associated field pea. Soil Biology and Biochemistry 28, Johansen, A. and Jensen, E.S Transfer of N and P from intact or decomposing roots of pea to barley interconnected by an arbuscular mycorrhizal fungus. Soil Biology and Biochemistry 28: