- Proportion of rainfall lost as surface runoff; thus also soil erosion;
- Volume of plant-available water in the rooting zone; thus also with implications for resistance to effects of climatic drought;
- Volume of water percolating down to the water-table, with implications for irrigation possibilities.
Organic matter: Organic matter is not merely a source of plant nutrients (albeit at low concentrations). It is also the substrate for soil organisms’ activity, so a regular supply is needed, as the organisms’ metabolism results in its transformation. Tillage is a potent cause of oxidation of organic matter - to atmospheric CO2 - having caused soil organic matter to be lost from soil faster than it is returned from conventional cropping systems, with negative effects on soils’ cation exchange capacities and thus on capture and slow release of plant nutrients from applied fertilizers.
Tillage can thus have two negative effects:
- Physical damage to soil structure;
- Provoking excess oxidation of organic matter.
Floods, water shortage (for plants, for rivers), sub-optimal plant growth, soil erosion are inter-related to sub-optimal conditions of soil porosity, associated with tillage. Optimum conditions of soil porosity can only be restored through the biotic activities of soil-inhabiting organisms.
There seems to be a widespread assumption that tillage agriculture is the only way to produce crops, onto which ‘soil management’, ‘erosion control’, ‘water management’ are seen as ‘add-ons’ rather than integral parts of the land-management system(s)..
is mentioned briefly, apparently as an option, in the paper summarizing the Salzburg Seminar. Its three interlocking component features are:
- Minimal disturbance of soil once brought to good condition;
- Maintenance of a permanent cover of organic materials (e.g. crop residues) on the soil surface;
- Crop rotations/sequences including legumes.
The interactions of the physical, chemical, biologic and hydric components of soil productivity are key to Conservation Agriculture’s success when functioning in good conditions of climate and management. These aspects of optimum CA, and its outcomes, deserve close study. These are features which any/all production systems should have in common, though their expression will vary from one situation to another (environmental and/or human). All too commonly their optimum combined expression has been damaged, obscured or unbalanced by inadequate land management in the past. CA, when optimised for a particular situation, is a means of achieving and maintaining the integration of crop (and even pasture and/or silvicultural) production with effective water management, erosion minimisation/avoidance, drought-effect minimisation, biodiversity in the soil, carbon retention in the soil, improvement of people’s livelihoods, and consequent wider benefits to both society and to the environment.
If the soil is kept in good condition (physical characteristics = ‘soil quality’; biological characteristics = ‘soil health’), all other attempts to improve the lot of farm-families have a better chance of lasting success than if the soil itself continues to degrade.
In a given situation, we need to be able to characterise the condition of the soil as it is, the condition of the soil as we would like it to be, how to get from the first condition to the second, and how to maintain the latter when we have got there.
The follow-through of these ideas indicate significant implications for research, advisory work, policy, education and training at all levels, and the ways in which AGRA can have fullest effects.