Agriculture sustainability?

Question

With each crop, we diminish the soil content in various minerals and compounds. Some of these minerals never come back to the ground. Most of them go into the cities sewage systems. If nothing is done then the quality of food (taste included) will continue to decrease and some plants won't even grow. Artificial fertilizers are not (by far) a complete solution since they cannot contain all the missing substance. Organic residues from sewage are polluted by detergents , chloride and other chemicals so they can't be used / transformed into fertilizers.

What are the choices we have for a sustainable agriculture? Thanks!

Answer 1

For this reason the concept of organic farming getting momentum. Use of balanced doses of chemical fertilizer, bio fertilizer, green manures,animal manure, recycling of crop residue, earthworm manure etc will  increase agricultural sustainability.

Answer 2

Sustainable agriculture as you are aware involves many more complex issues than the one you bring up regarding soil fertility and nutrient removal from the soil, but Ill try to address this one in my answer.  The key to sustainable agriculture is in maintain a healthy soil enviorment and returning as much or more back to the soil than you take away from it.  Turning the soil over to the next generation in as good or preferably better condition than you received it.  You bring up a couple of interesting questions.  Many of the nutrients are returned to the soil as organic matter in the form of crop residue.  Some are removed in the in the form of produce, grain, etc.  These must be replaced.  There are several ways to replace these nutrients.  One is fertilizer, that you mentioned, this usually replaces the major nutrients removed by the crop.  Too much fertilizer has negative effects on the soil and water which is not in line with the goals of sustainable agriculture.  Much of these nutrients including the micro nutrients removed can be replaced with animal manures, organic composts, activity of earthworms, etc.  Most of the micro nutrients removed by the crop are in very small amounts and the soil  usually containes fairly large amounts of them, so they usually are not a big problem.  They do need to be returned to the soil, however, or the eventually will become a problem.  Your point about permanent removal of nutrients by sewage is a valid point.  Sewage can and is being converted into safe fertilizer in some cases.  I think in order to maintain sustainable agriculture over the ages that all human sewage will need to be returned to the soil.  It won't likely be in our life time, but only so much can be removed from the earth. For example only so a finite amount of phosphorus can be mined from the earth.  Recycling all nutrients will some day be the only source available of some nutrients.  For the present, work must be done to make all human waste safe to recycle to the soil.

Answer 3

Sustainable agriculture, as with the overall concept of sustainability in general, involves a whole range of complex issues. Nutrient removal and replenishment is just one among many. In tropical clay soils, even mechanized tillage poses future problems because of the "hardpanning" below the plough layer.

I would say that the key concept in sustainability is the attempt to achieve balance between current need, eg. productivityity and future productiv capacity. As with sustainability in general, this must also  be balanced with other environmental concerns, such as ozone depletion, greenhouse gas emissions (of which extensive grain production is a major contributor, especially wetland rice), maintaining soil structure, ensuring sustainable water for irrigation (and also ensuring limited runoff and chemical residues), etc.

And its all about making choices - what makes sense now, given the level of knowledge - and what the future requires. In so many cases, its hard to have all the answers, but we can keep on trying.