Soil test phosphorus and cumulative phosphorus bud

Authors: Aimé Jean Messiga Noura Ziadi Claire Jouany Perttu Virkajärvi Raija Suomela Sokrat Sinaj Gilles Bélanger Ciprian Stroia Christian Morel

Publish Date: 2015/02/15

Volume: 44, Issue: 2, Pages: 252-262

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Abstract

We analyzed the linearity of relationships between soil test P STP and cumulative phosphorus P budget using data from six longterm fertilized grassland sites in four countries France Ercé and Gramond Switzerland Les Verrières Canada Lévis and Finland Maaninka and Siikajoki STP was determined according to existing national guidelines A linearplateau model was used to determine the presence of deflection points in the relationships Deflection points with x y coordinates were observed everywhere but Maaninka Above the deflection point a significant linear relationship was obtained 033  r 2  072 at four sites while below the deflection point the relationship was not significant with a negligible rate of STP decrease The relationship was not linear over the range of STP encountered at most sites suggesting a need for caution when using the P budget approach to predict STP changes in grasslands particularly in situations of very low P fertilization Our study provides insights and description of a tool to improve global P strategies aimed at maintaining STP at levels adequate for grassland production while reducing the risk of P pollution of waterThe difference between fertilizer phosphorus P inputs and crop P exports referred to as the P budget is often used to assess P management in agroecosystems Watson et al 2002 Serrano et al 2014 and to predict soil P changes over time Messiga et al 2012a Morel et al 2014 The annual P budget is the key component of global P strategies aimed at lowering the P content of Psaturated soils and monitoring the risks of P pollution of water Reijneveld et al 2010 In Finland negative P budgets are recommended to farmers to reduce the high soil P content of their soils Saarela et al 2004 Valkama et al 2009 In France the national P budget was reduced to 44 kg ha−1 year−1 in 2006 as a result of reducing P inputs to agricultural soils Senthilkumar et al 2012a while it decreased steadily in Switzerland during the period 1975–2008 to stabilize at 55 kg ha−1 year−1 Oehl et al 2002 Spiess 2011 In North America particularly eastern Canada less emphasis is placed on the P budget in P fertilizer recommendations instead the probability of an economic response of crop yield to P fertilizer applications is the central concept of P fertilization strategies CRAAQ 2010Results from longterm experiments with annual field crops Morel et al 2000 Tunney et al 2003 and perennial grass crops Messiga et al 2014a Morel et al 2014 have shown that soil test P STP is closely and positively related to cumulative P budget B cumP This relationship has been shown to vary with location Blake et al 2003 soil type Ciampitti et al 2011 crop rotation Oehl et al 2002 and tillage system Messiga et al 2012b However for a given site it is not affected by different rates of N fertilization applied to forage grasses Messiga et al 2014a Studies with annual field crops have shown that a single linear regression can describe changes in STP for both negative and positive P budgets Blake et al 2003 For instance Messiga et al 2010 grouped data from a maize Zea mays L monoculture in France following 7 12 and 17 years of cultivation and demonstrated that a single linear regression described changes in STP over the three periods This indicated no or little variation between the parameters of the linear regression in this maize monoculture for a wide range of STP and B cumPThe linearity of the STP–B cumP relationship over a wide range of STP values as a result of varying P fertilization rates has not yet been studied in longterm and semipermanent grasslands In zeroP plots Ma et al 2009 reported that STP decreases with time until no further additional decrease can be observed Under fertilized notill management systems Messiga et al 2012b observed a more than proportional change in STP for a unit of P budget due to the effect of residual P derived from fertilizer The P fertilizer applied to grassland is not mixed with the soil and crop residues Whitehead 2000In this study we hypothesized that in longterm grassland fertilized with varying P rates the relationship between STP and B cumP will not be linear over a wide range of STP values To investigate this we assembled a dataset of cumulative P budgets and STP values from six longterm grassland sites with different soil characteristics in four countries Canada Finland France and Switzerland The objective of the study was to analyze the linearity of the relationship between STP and B cumP in a number of grassland experiments covering a wide range of STP values obtained as a result of longterm applications of varying P fertilizer rates To set future national P budget targets that account for both grassland production and water protection improved and updated knowledge about longterm impacts of current global P management strategies on changes of STP levels is needed

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