An analysis of farmers’ use of phosphorus fertiliser in industrial agriculture: a case study in the Bordeaux region (south-western France)

Abstract

Global phosphorus (P) reserves are rapidly being depleted and agriculture is a major contributor to P consumption worldwide. Moreover, agricultural P use may lead to local excess of P in soils, resulting in water eutrophication. To remedy this situation, it is necessary to understand the key factors underlying P use by farmers within such a context. The objective of this article is to understand how farmers use P fertilisers under agricultural conditions. Particular attention was paid to the use of conventional decision-making tools such as soil analysis by farmers. Industrial agriculture, characterised by high levels of specialisation, input use and production yields, was considered as a case study. Forty farmers involved in industrial agriculture in south-western France were interviewed in 2008 about their P use. Soil analyses were collected when available. Input/output P balances were computed at the plot scale. Moreover, records of farmers' fertilisation practices were analysed from a database developed by a technical advisory group. Results showed that 90% of farmers had a crop-specific and yearly P fertilisation strategy. This yielded very positive P balances for vegetable crops. Few farmers used recommendations based on soil analyses: in most cases, the amounts of P used by the farmers were lower than those recommended. When asked for their opinion about the role of P in agriculture, most farmers explained that P fertilisation helped boost the growth of spring crops in the event of adverse weather conditions. This revealed the emphasis placed on ''plant-based'' strategies for P management, as opposed to ''soil-based'' strategies, thus reinforcing annual fertilisation strategy. This study provides a foundation for understanding key factors underlying P consumption in agriculture.

Higher flexibility in input N:P ratios results in more balanced phosphorus budgets in two long-term experimental agroecosystems

“…Using low N:P poultry manure as the only external input to meet crop N demand resulted in 439 substantial P surpluses and low PUE compared to other systems, consistent with previous studies 440 ( Kleinman and Sharpley, 2003;Bergstrom et al, 2008). This illustrates the consequences of 441 considering P inputs as a secondary concern when applying manure in N-limited systems 442 (Nesme et al, 2011). We have shown previously that excessive P applications compared to crop 443 demand resulted in soil P accumulation and saturation of the P sorption capacity in these systems 444 (Maltais-Landry et al, 2015).…”

“…Systems receiving mineral fertilizers where N and P inputs can be decoupled had more 474 balanced P budgets than those fertilized with manure, consistent with findings of Oehl et al 475 (2002). However, P surpluses also occur with mineral fertilizers (Cao et al, 2012), especially in 476 vegetable production (Oelofse et al, 2010;Nesme et al, 2011;Yan et al, 2013). The systems 477 receiving only mineral fertilizers in our study were close to P balance, and given their N:P ratios, 478 they did not accumulate soil P substantially (Maltais -Landry et al, 2015).…”

“…This was likely due to the N limitation of corn yields in the organic and mixed systems that 505 resulted in lower P uptake, as corn and wheat often have similar P balances (Nesme et al, 2011). 506…”

Reducing soil phosphorus fertility brings potential long-term environmental gains: A UK analysis

“…Firstly, many farmers do not get their soils tested either at all, or routinely, and therefore do not regularly monitor soil P fertility to optimise their nutrient inputs for maximum efficiency. They instead rely on historic fertiliser management practices which may no longer be relevant or appropriate, and leave large P surpluses in the soil (Nesme et al 2011). Secondly, it is unclear whether maintaining an agronomic optimum STP still poses a eutrophication risk for some waterbodies.…”

Regional-scale phosphorus flows and budgets within France: The importance of agricultural production systems

“…However, this hypothesis was rejected in Aquitaine, probably for the reasons explained above. This poor substitution may be due to technical difficulties in replacing mineral fertiliser with animal manure, e.g., placement on the sowing row, low P concentration in manure or lack of P availability (Nesme et al 2011). It may also result from a small but significant share of stockless farms that would not use animal manure within the region considered.…”