Summary of Counter-Arguments:
| - Organic farms usually implement a range of practices that increase phosphorus inputs and phosphorus recycling and reduce phosphorus losses at the farm level. - Synthetic P fertilizers are made from rock phosphates that are chemically modified. Organic Agriculture allows the use rock phosphates (PRs) that are only physically (mechanically) modified. They are less energy intensive, more affordable, better for building the soil’s long term fertility and as easily transportable as the chemically modified phosphorus. |
Details of Counter-Arguments:
The question of replenishment of phosphorus levels in tropical organic agricultural systems is indeed seen by many agronomists as one of the main challenges for the long-term productivity of organic farms. The problem is assumed to be more serious in Sub-Saharan Africa because the soluble content of phosphorus on bedrock is quite low in many regions. However, many field observations suggest that the phosphorus “nutrient cycle problem” is not more difficult to solve in Organic Agriculture than in conventional agriculture.
When considering Organic Agriculture at the farm level, there are several possible inflows of phosphorus. Organic inputs can be brought from outside the farm (e.g., through grazing, collection of wild products, and organic amendments such as peat, guano, and seaweeds). Agro-forestry practices can also increase the nutrient take-up from the subsoil through the deep-penetrating roots of trees (and other perennial crops).
Organic standards permit the use of clay and rock phosphates (PR), both of which containing phosphorus. Although the use of rock phosphates is not currently common in tropical countries, and in Africa in particular, there is considerable potential for improvement in extraction methods and also regarding transport and distribution to farmers that would assist countries in Africa and tropical countries outside of Africa in the use of rock phosphates. There are substantial deposits in various countries across Africa and some of these countries, such as Togo, Senegal, Morocco, and Tunisia, even export to the world market. In addition, many rock phosphate deposits located in the tropics and subtropics are still un-tapped. [1] Countries like Mali and Burkina Faso have deposits that they want to develop for local markets, with the intention of increasing the use of rock phosphate and replacing imported fertilizers. Further anticipated developments, including improvements in economies of scale, and logistics, more and more farmers will have access to natural phosphates when needed. Technically, there is no reason why the transportation cost of natural phosphate (per unit of P) should be higher than the transportation cost of synthetic phosphate. Indeed, rock phosphate has a concentration between 32 and 35 percent p205, which is comparable to the concentration of synthetic phosphorus fertilizers (most traded superphosphates average 36 percent p205, while single superphosphate is sold in some markets with a p205 content of around 18 percent).
Except for some nitrogen-based fertilizers, almost all conventional, chemically processed ‘industrial’ fertilizers are chemically processed rocks. Synthetic P fertilizers are derived from rock phosphates that have been chemically modified. In contrast, agrominerals used in Organic Agriculture are commonly only physically modified, by crushing and grinding. [2] The production of rock phosphate relies on the same raw materials as production of chemically processed P fertilizers, but is less energy intensive. Superphosphates have high energy cost components and are already too expensive to be affordable in adequate amounts by low output farmers–unless continuous subsidies are provided by taxpayers or donors. The difference is that, in most conditions, phosphorus from rock phosphate is not as immediately available to plants as superphosphate (which is water soluble by treatment with acid); it is broken down into forms available to plants over a longer period (e.g., five years). It is nevertheless possible to use several biological means to increase the availability of P from rock phosphate in the first years (e.g., phospho-composting, inoculation with vesicular-arbuscular mycorrhizal fungi, use of phosphate solubilizing micro-organisms that enhance PR dissolution and P availability to plants). Many leguminous plants (which are commonly used in typical organic rotations) also facilitate the solubilization of rock phosphate. Moreover, by reducing Ca activity in the soil solution, the presence of organic matter (Ca-sink) in the soil helps to quicken the dissolution of PR. Hence, the impact of PR application will be realized more quickly in a well-managed organic field. However, organic is a long term project [3]. Organic practitioners understand that building healthy and truly fertile soil takes time, which is one of the reasons they employ techniques that work over longer periods of time than the growing season. Bringing readily soluble, synthetic fertilizers to the soil will only provide from one to three nutrients for the current growing season, but will undermine the broader fertility of the soil in the mid to long-term. On the contrary, rock phosphates and other natural mineral fertilizers commonly have long-term residual effects and contribute to recapitalization of nutrients in the soils.
The current loss of phosphorus observed in Africa, also has a lot to do with the fact that a large percentage of Africa’s food producing areas consists of farming characterized by very small family farms that have very little access to any kind of inputs (synthetic and natural P fertilizers alike). This means that alternative ways of improving the nutrient balance have to be developed and implemented, and that reducing nutrient losses on the farm will play a major role. Organic Agriculture can significantly reduce the outflow of phosphorus from the farm through recycling of crop residues and animal wastes and because it results in higher organic matter content in the soil, which helps reducing erosion and nutrient run off and increases the soil’s cation exchange capacity (CEC). Phosphorus consumed by both humans and animals is rejected through their waste. Too often, nutrients contained in these wastes end up getting flushed into waterways, disturbing their ecosystem and ultimately causing water pollution and insalubrity problems. Recycling animal wastes (including bonemeal, chicken manure and bat droppings) and human wastes through on-farm composting and, perhaps, ecological waste (water and solid) management systems could help significantly reduce the phosphorus losses.
While studies of soil fertility at the national level in Africa present negative nutrient balances (even under conventional agriculture), the picture is more varied at field and farm levels where households have developed a wide range of management strategies [4]. It is often hard to quantify the effect of organic management practices on nutrient cycles because of the fact that Organic Agriculture isn't about like-for-like input substitution, but rather the overall development of healthy soil. Unlike synthetic fertilizers, organic fertilizers often have a complex and variable nutrient composition, which makes the collection of data a much more complex enterprise. A related problem is the lack of research on organic and natural mineral fertilizers (e.g., less research tends to be done on rock phosphate than on synthetic P fertilizers since fertilizer manufacturers have an economic interest in selling superphosphates). Agricultural research institutes and extension services are also still convinced that chemically-processed fertilizers are indispensable.
Let’s also not forget that, although low soil fertility is one cause of Africa’s food insecurity, it is certainly not the only cause. Social and economic determinants are at least as important. There is increasing evidence that it is not only supply factors, such as productivity per hectare, but rather demand factors, such as market opportunities and access, that determine agricultural development outcomes in Africa. Organic agriculture, by offering new and rewarding market opportunities for African smallholders, can help rural families find a way out of poverty, and can provide them with the incentive to invest in enhancing the soil fertility of their land holdings. [1] Use of Phosphate Rocks for Sustainable Agriculture (FAO, 2004) http://www.fao.org/docrep/007/y5053e/y5053e00.htm
[2] The reader may want to check on the excellent book written by Peter van Straaten: Rocks for crops, available online at http://www.uoguelph.ca/~geology/rocks_for_crops/
[3] This is addressed in the IFOAM Basic Standards, which state that “Mineral fertilizers shall only be used in a program addressing long-term fertility needs..”.
[4] Nutrients on the Move: Soil fertility dynamics in African farming systems, Thea Hilhorst and Fred Muchena (2000).