Organic Source of Nutrients: Some Simple Computations Please

One of the aspects in promoting more sustainable agriculture for smallholders in developing countries is to promote enhanced nutrient cycling by relying on organic sources of plant nutrients. Many host governments have highly endorsed the concept in the expectations of saving scarce foreign exchange required for importing mineral fertilizers. However, before getting overly committed to organic fertility with potential catastrophic consequences, there may be a need for a reality check on just how much organic material is available relative to that needed for the commercial crops essential for poverty alleviation, as well as the time and energy required to recover the organic nutrients relative to the energy derived from increased agronomic production obtained from their use. To consider anything less than a commercial crop would most likely inadvertently promote poverty entrapment.

Zero Sum Movement

Except for legumes or blue green algae in paddies that can fix nitrogen, organic sources of plant nutrients do not represent a new source of fertility. Instead they are primarily simply a movement of very bulky supply of mineral fertilizer within the confines of a production area in what can only be, at best, a zero sum effort. That is there will be a source that will be losing fertility in order to have a field gaining in fertility. Thus to be effective and sustainable it is necessary to determine the ratio of area from which the organic nutrients need to be collected to the area over which they will be distributed. Typically, if a commercial grain crop such as rice removes 2/3 rd of the mineral nutrients with the grain and this is sold outside the area or consumed and recoverable nutrients deposited in “night soil”, then if the fertility recovery process is 100% efficient it will require 3 ha of crop residues to provide sufficient organic nutrients to fertilize 1 ha of future rice fields. How often will smallholder communities have this much land available for every hectare of cropped land? Likewise, if this land is also being cultivated, how will it be fertilized? It is also unlikely the recovery will be 100% efficient thus additional source land will be required to accommodate the inefficiencies in the recovery process.

Similarly, it was estimated in an AIT MSc thesis based in Mindanao, Philippines that it would require 4 animal units to provide sufficient manure to fertilize one hectare of maize land. Each animal unit would require 1.25 ha of unimproved communal grazing lands. Thus, for animal manure to be effectively utilized as the primary source of fertility to produce a commercial crop, it would require 5 ha of grazing land for each ha of crop land. Is this really very practical in most smallholder communities?

Supply Of Organic Material

Similarly it is important not to over estimate the supply of organic material. For example, an organic farming project in a banana production area of Uganda recommended 1 wheelbarrow of organic material for every square meter of area. How much does this amount to? A wheelbarrow is not a very precise measurement, but a good wheel barrow load of organic material might weigh 30 kg. Thus, for a hectare of organic bananas it would take 10,000 wheelbarrow loads at 30 kg each for a total of some 300 tons of material. How realistic is this? What plants or ecosystems can generate this amount of organic material and what area would be required? Wouldn’t this be a challenge even of nepier grass, the world’s largest forage producer? Over what distance would this have to be transported? Would some simple evaluations of the material available and computations of distance over which it has to be transported, etc, avoid some unrealistically embarrassing recommendations and projections? Would this be another case of what can be concentrated and demonstrated on small areas quickly losing its validity when extended to a full hectare or farm? Something the smallholders will quickly realize, much to the discredit of the promoters.

It should also be noted that most organic farms in the USA are not usually fully independent in nutrient cycling, but dependent upon neighbors with animal operations to provide the manure that represents a net import of plant nutrients to the organic farm replacing what was removed with the marketed crop and allowing organic farms to be sustainable.

Time and Effort

Organic material tends to be very bulky to handle. Normally it will have a nutrient content of no more than 2 or 3% of the dry weight, and considerably less for fresh weight. Thus, it would require some 7 tons of material to be accumulated, transported, and distributed to obtain 200 kg of N, P, & K nutrients typically recommended for a commercial crop using mineral fertilizers. While this is substantially less then the 300 t suggested above, it still requires a substantial amount of physical effort and will require considerable amount of time and effort even if assisted with a bullock cart. Also, when will smallholder actually have the time to undertake this extensive operation? During the dry season when the soils are too hard to easily work?

The amount of time and effort required to utilize organic nutrient materials raised the question what is the caloric energy balance? That is, what is the physical effort and the calories exerted to utilize organic nutrients relative to the calories recovered through the increased yields that result from their use? In developed countries where organic cycling is done under a luxury consumption diet and people are not dependent on organic cycling in their home gardens for their primary substance, it is possible to exert more calories than are recovered and write it off to needed and healthy physical exercise. However, for smallholders in developing countries that are deriving virtually all there substance from the production of the land, there are no surplus calories to exert, and they have to recover more calories from the increased agronomic production than they exert in the organic nutrient recovery, or they could become more severely under nourished, and either lose weight or become more lethargic in the afternoons as discussed in the oversights of the basic premise, and options for undernourished farmers. An example might be that if a smallholder trying to recover organic nutrients is exerting some 280 calories each hour, then the increase in agronomic production will have to be 102 g of paddy rice, 77 g of maize, 175 g of cassava or 229 g of plantain per hour of effort just to balance the energy being exerted. Anything less would result in a negative energy balance and not be sustainable. It also has to be appreciated that this additional production, if actually obtained, will not be available until the next harvest, perhaps some 6 or more months in the future. Perhaps this is one reason why organic nutrient cycling in smallholder communities rarely goes beyond the homestead garden, and then more as a waste disposal problem than nutrient recovery effort.

Grazing Stubble

Perhaps the most effective means of promoting nutrient cycling in smallholder communities is to graze crop stubble. This is actually fairly common. In Egypt the nomadic Bedouins will contract with farmers in the main crop lands of the Nile Delta for their migrating herds of sheep and goats to graze on crop stubbles. Since this is not manufacturing nutrients, the best that might be said is that it is converting crop stubble from a form that is normally burned for lack of power to incorporate into the soil, to a form that is easily and normally incorporated into the soil. With the limited resources normally available to smallholders to manage their land and incorporate crop residues and the need to exert less energy than they derive from the land, this might be the best prospects for sustainable organic nutrient recovery.

Compost and Green Manure

While both compost making and green manure crops can be easily demonstrated in small plots or on a small scale near a homestead, they are most likely “non-starters” as a major source of fertility from the smallholders’ perspective. As discussed above, compost requires additional processing rather then simple using crop residues because it takes just too much time and effort to accumulate the material, compost it, and then redistribute it, and most likely the energy exerted will exceed the energy derived from the additional agronomic yields, to say nothing about the delay between energy exerted and energy recovered. The latter happening only after the next crops are harvested. Secondly there really is just not enough material available to effectively provide organic nutrients for an extended farm area.

Green manure is dependent on the surplus labor that as expressed elsewhere may be more myth then reality. It depends on farmers deliberately delaying basic crop establishment, when they are more likely hard at work on another parcel. Also, farmers working with anything short of 4-wheel tractors will have difficulty incorporating dry crop residue from the previous crop and, it will be even more challenging to incorporate a fresh green manure crop.

Summary

While there is little environmental harm in promoting enhanced organic nutrient recovery, smallholders will very quickly recognize the limited application. This could affect the overall creditability of the promoters. It might be more creditable to concentrate on other more realistic approaches to more sustainable agriculture, then continuing to promote ideas that are well outside the resource base for the farmers to seriously consider and can predictably be rejected with a little forethought and some quick calculations. In promoting organic fertilizer utilization for smallholders it is necessary to again recognize the limited supply of organic material as well as the limited resources farmers may have to implement the suggestions, and the limited prospects to recover the manual energy exerted.

Last Revised: 14 Aug. 2006.