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Definitions (1)Soil:An ecological system consisting of inorganic minerals, decomposing organic matter, living organisms and growing plants.Soil is a complex living system: >> 10,000 different species in 1 g of soil >> 1.5 as many individual organisms in a teaspoon of soil as people on earth
Definitions (2)Soil health (synonym soil quality):Ability of a soil to * enhance productivity; * regulate water flow; * buffer environmental changes; * support environmental, animal and human health;in a sustainable way.
Definitions (3)Soil health according to SSSA:Capacity of specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, to maintain or enhance water and air quality, and to support human health and habitation.
Soil health: Physical fertility Chemical fertility Biological fertilityFocus on the biological fertility
Biological soil quality includes: Biomass and biological activity Biodiversity (no. of species and their abundance) Disease suppression (various mechanisms)
Potato diseases and pests Over 300 potato pests and diseases world-wide About 140 are serious Include viroids, viruses, phytoplasmas, bacteria, fungi, nematodes, insects and parasitic weeds Many are soil-borne
Crop rotationMore or less fixed pattern in the succession of cropson a certain field.Relevant aspects are: Which crops are part of the rotation Frequency of each crop Sequence of cropsAll aspects affect disease pressure.
Potato stems affected by Rhizoctonia (%)Rotation No nematicide With nematicide AverageP 48 62 54MP 22 41 32SP 23 32 28MSBBP 9 14 12Average 26 37
Potato stems affected by Verticillium (%)Rotation No nematicide With nematicide AverageP 49 34 42MP 39 20 30SP 50 38 44MSBBP 21 13 17Average 40 26
Potato stems affected by Colletotrichum (%)Rotation No nematicide With nematicide AverageP 35 32 34MP 29 30 30SP 33 36 35MSBBP 28 27 28Average 31 31
Average (6 years) early tuber dm yield (g/m2)Rotation No nematicide With nematicide AverageP 99 122 111MP 131 144 138SP 118 154 136MSBBP 152 167 160Average 125 147
Comments on these results: Synergistic and antagonistic effects occur It is possible to influence such effects by cultural practice Level of other inputs must be adapted
A new trap cropTwo greenhouse experiments (2003 and 2004) with containers cropped to susceptible potato cv. Bintje, S. sisymbriifolium (sticky nightshade) and fallow- Cysts in nylon bags buried in soil with different crops or fallow and dug up at different times- Assessment of root density around each bag
100Luring of nematodes from their 80 60 cysts (%) 40 20 Bintje Raketblad 0 0 1 2 3 4 5 6 7 -3 Root length density (cm cm )
Effects of oats on relative numbers (%) of mesofauna and Rhizoctonia index Rel. no. of Rel. no. of Disease index (0-100) collemboles nematodes Year 1 Year 2 Year 2 Year 1 Year 2Control 100 100 100 26 67Oats 127 123 1043* 10* 51*
Use your own seed tubers (farm-specific seed) Figure 1. Schematic representation of interactions that may play a role in potato Rhizoctonia-decline in seed potatoes disease Rhizoctonia- suppressing microorganisms population in the soil in the soil
Disease suppression:Trial field Wildekamp, The Netherlands, sandy soil Grassland (50 years) ⇒ ⇒ G permanent grassland G → AM monoculture maize G → AR crop rotation (oats, maize, barley, potato) Arable land (20 years) ⇒ ⇒ A→G grassland A→M monoculture maize A→R crop rotation (oats, maize, barley, potato) (Garbeva, 2004)
Disease suppression (Potato with Rhizoctonia) Diversity: Shannon Weaver index with PCR-DGGE rotation % bacteria fungi Bacillus actinomycetes healthy G → AM 100 3.51 3.26 2.85 2.75 G → AR 60 3.55 3.24 2.85 2.55 G 60 3.24 3.35 2.85 2.34 A→M 30 3.10 2.90 2.25 2.45 A→R 17 3.10 3.02 2.13 2.40 (Garbeva, 2004)
Changing biological diversity by importing beneficialmicro-organismsEffective and Beneficial Microorganisms (EM)include1. Photosynthetic bacteria2. Lactic acid bacteria3. YeastsThey provide useful substances to the soil faunaand stimulate breakdown of organic matter.They also contribute to suppressiveness?
An example of system experiment to test how farwe can go with non-chemical enhancement of soilhealth Aim: control a complex of soil-borne pathogens with ecologically sound techniques Method: Grow potato in a narrow rotation (1:2), infest with nematodes and fungi, and clean with several techniques Grow potato cultivars highly resistant, moderately resistant and susceptible to Globodera pallida.
Soil infestation: Nematodes: Meloidogyne hapla, M. chitwoodi, Pratylenchus penetrans, P. crenatus and Globodera pallida Fungi: Rhizoctonia solani, Verticillium dahliae
Non-chemical control techniques: Use of resistant cultivars (3 levels; HR, MR, S) Use of green manure crops (3 levels: fallow, African marigold, oats) Use of trap crop against PCN (2 levels: control (fallow), potato) Use of removal of potato haulm (2 levels: left on the field or removed)36 treatment combinations in three replicatesExperiment duplicated and each duplicate running for 5 years
Experiment stopped after 5 years because ofbudget cuts and early retirement of principleresearcherEffects of use of trap crop on all pathogensknownResults averaged over 3 green manure crops x2 haulm treatments x 3 cultivar combinations
Main results of system experiment for one duplicate Control Trap P cropNo. Meloidogyne spp. / 100 ml soil 0 36 <0.001No. Pratylenchus crenatus / 100 ml soil 184 190 nsStem infections with R. solani (index 0-100) 52 50 nsBlack scurf on tubers (index 0-100) 22 10 <0.001Stem infections by V. dahliae for cv. S (%) 42 22 <0.05No. cfu per g soil of V. dahliae 61 37 <0.01Fresh tuber yield for cv. S (g/m2) 4540 5210 <0.05Note trap crop is for PCNcv. S is PCN susceptible cultivar
Conclusions: Interactions between soil organisms are important for control of soil-borne pathogens (sbp); Soils can suppress certain sbp; Organic amendment approaches are most likely more successful in controlling sbp than introductions of single species; Root length density is important for trap crops; Biodiversity is important to make management strategies reliable.
AcknowledgementThis contribution was partly based on the heritage of Dr K. Scholte, former co-worker at the former Department of Agronomy, WUOther information came from the Crop and Weed Ecology group (WU), Soil Quality group (WU), Louis Bolk Institute, numerous websites and Science