When humans or animals are concentrated regionally, inadvertent environmental impacts are bound to occur. Let us take a look one of the agri-environmental impacts of livestock concentration:
Feed demand of large numbers of livestock exceed local feed supply --> Feed is imported --> Livestock excrete large amounts of manure --> Excess manure phosphorus creates a regional phosphorus imbalance for the agricultural soil.
What is "Phosphorus (Im)Balance"?
Phosphorus balance is essentially a simple mass balance equation that includes phosphorus input and output of the agricultural top soil:
Phosphorus balance = Input (e.g., manure, fertilizer) - Output (e.g., harvested crop)/ Agricultural Land
Input, output, and agricultural land data are typically obtained from regional or national organizations that keep statistical records.
Organization of Economical Cooperation and Development (OECD) uses phosphorus balance as an agri-environmental indicator and regularly publishes the national balances of its member countries which include USA and Turkey.
You can see the national phosphorus balances of OECD member countries for the periods of 1990-1992 and 2002-2004 from here.
So, what does "phosphorus imbalance" indicate?
If agricultural soil has positive imbalance,
- Phosphorus may become a limiting nutrient, crops may suffer fromphosphorus stress, and subsequently crop yields may decrease.
If agricultural soil has negative imbalance,
- Phosphorus may be applied in excess of crop needs, accumulate in soil, and cause eutrophication if transported to surface waters
Hence, positive and negative imbalance indicate risks that can threaten food security and aquatic ecosystem quality, respectively, if they are materialized.
Scale does matter: national versus regional balances
Spatial distribution of phosphorus imbalance can be resembled to wealth distribution. Some have a lot whereas some have little. Therefore, national phosphorus balances can mask regional phosphorus imbalances. Policymakers can look at the national balance values and can easily say:
"Phosphorus balance of our country looks not too bad..."
Such an assessment can easily translate into inaction and exacerbate the situation in regions with significant and persistent phosphorus imbalance problem.
Influence of poultry industry on regional phosphorus imbalance: a Turkish case
Turkey is the sixth leading poultry meat exporter in the world. Between 1990 and 2007, annual broiler meat production in Turkey increased almost seven-fold, exceeding one million metric tons (Güngör, 2013). The country is also an OECD member that has a moderate positive annual phosphorus imbalance hovering around 5 kg P/ha.
Out of curiosity, I applied the OECD phosphorus balance method on Bolu province which is a preferred region of the poultry industry. The province has experienced a tremendous growth in terms of broiler production in the past few decades. To my knowledge, this is the first study of its kind precipitated in Turkey.
I found that phosphorus imbalance of Bolu tripled the national imbalance (please see years 2003 & 2004 in the figure below) indicating a clear mismanagement of a valuable and non-renewable agricultural nutrient and associated environmental pollution risk. The percentages shown over each bar in the figure are the phosphorus use efficiency. The phosphorus use efficiency figures of Bolu indicates that the province only convert 1/3-1/4 of the available phosphorus into crops
I must also highlight the fact that Turkey is a country that (a) lacks significant phosphate rock reserves to be used in the fertilizer production like many other countries in the world, (b) its farmers almost constantly complain about the high fertilizer prices, (c) has eutrophic lakes.
Therefore, when you hear people talk about agricultural or environmental sustainability, please remember this point and be aware that we need to be good stewards of our non-renewable resources, including but not limited to, phosphorus.
Figure Reference: Güngör (2013)
