DIAGNOSIS OF SOIL RELATED CROP PROBLEMS Second version Spring 2020 Gerard J.M. Oomen .............................................................................................................................. 6 Diagnosis of soil related crop problems ................................................................................ 1 Introduction ................................................................................................................. 7 How to use this document ............................................................................................... 7 Organic agriculture ........................................................................................................ 8 Diagnosis of individual plants ........................................................................................... 10 Finding causes of poor performance. ............................................................................... 10 During Germination and emergence ............................................................................ 10 Between emergence and flowering ............................................................................... 10 During Flowering and ripening ..................................................................................... 12 Causes of poor performance ............................................................................................ 12 Too low plant density and too weak seedlings ................................................................... 13 Causes not related to soil properties............................................................................. 13 Causes related to soil properties and what can be done ................................................... 14 1. Soil organisms may have eaten seeds and seedings before emergence ................ 14 2. Emerging plants may have been affected by soil or seed borne diseases. ............. 14 3. Seeds did not germinate simultaneously ......................................................... 15 4. A part of the seeds and emerging plants may have suffocated ........................... 15 5. A part of the seeds could not penetrate a crust ................................................ 15 6. The seed was sown too deep ........................................................................ 15 7. The seed was sown too late or too early under cold and wet conditions ................ 15 Availability of water ..................................................................................................... 17 Possible causes of water shortage and what can be done ................................................. 17 1. Top soil is too loose after tillage .................................................................... 17 2. The soil does not retain enough water ............................................................ 18 3. Cappilary rise is impeded. ............................................................................ 19 4. Too much water is lost by run off .................................................................. 19 5. Too much water is lost by unnecessary evapo-transpiration ............................... 20 6. Water uptake is impeded by an infection of the root system .............................. 21 Availability of oxygen in soil .......................................................................................... 21 Possible causes and what can be done ......................................................................... 22 1. Sealing/slaking of soil surface ....................................................................... 22 2. Compaction of top soil ................................................................................. 22 3. Low permeability of sub soil ......................................................................... 22 4. High water table. ........................................................................................ 23 Availability of nutrients ................................................................................................. 23 Soil tests ................................................................................................................. 23 By a soil test laboratory ......................................................................................... 23 Quick Field tests ................................................................................................... 24 Diagnostic field experiments/pot experiments ............................................................ 24 Visible symptoms of deficiency ................................................................................ 25 Availability of nitrogen .................................................................................................. 27 What can be done ..................................................................................................... 28 To increase nitrogen fixation ................................................................................... 28 To reduce leaching of nitrogen beyond root zone ........................................................ 29 1. Increase water and nitrate retention .............................................................. 29 2. Support preferential flow of water ................................................................. 30 3. Reduce nitrate content in soil low by growing catch crops .................................. 30 4. Avoid an over-fertilisation ............................................................................ 30 To reduce losses by volatilisation ............................................................................. 31 1. from solid manure ...................................................................................... 31 2. from liquid manure and slurry ...................................................................... 31 3. from crop residues...................................................................................... 31 To reduce losses by denitrification ............................................................................ 31 1. Improve drainage ....................................................................................... 32 2. Prevent sealing of soil surface....................................................................... 32 3. Improve soils structure................................................................................ 32 4. Avoid compaction ....................................................................................... 32 5. Avoid deep incorporation ............................................................................. 32 6. Avoid freezing of green manure crops ............................................................ 32 Availability of phosphorus ............................................................................................. 32 Possible measures to improve availability of phosphorus .............................................. 33 1. Improvement of soil structure ...................................................................... 33 2. Support mycorrhizae ................................................................................... 33 3. Increase of pH of acid soils .......................................................................... 34 4. Decrease of pH in alkaline soils .................................................................... 34 5. Application of inorganic phosphate fertilisers ................................................... 34 6. Import of organic phosphorus ....................................................................... 34 7. Creation of hot spots ................................................................................... 34 8. Increase of organic matter content to reduce fixation ....................................... 34 9. Increase of C/P ratio of organic matter ........................................................... 34 10. Redistribution of organic phosphorus ............................................................. 35 Availability of potassium. .............................................................................................. 35 Possible measures to reduce losses .......................................................................... 36 1. Reduction of leaching .................................................................................. 36 2. growing less potassium rich crops ................................................................. 36 Possible measures to improve availability of potassium ................................................ 36 1 Stimulation of weathering ............................................................................ 36 2 Import of feed, bedding material and manure................................................. 36 3 More precise fertilisation .............................................................................. 36 4 In case of potassium fixation: adapt crops to availability of potassium ................. 36 Availability of sulfur ..................................................................................................... 37 Possible measures to improve availability of sulphur ................................................... 38 1 reduction of Leaching by growing catch crops. ................................................. 38 2 Import in feed, bedding, manure and inorganic fertilisers ................................. 38 3 Use local sources .......................................................................................