Yield response models to phosphorus application: a research synthesis of Finnish field trials to optimize fertilizer P use of cereals

Abstract

Fertilizer applications should be based on relevant yield response models and be economically justified. In this study, we defined the yield response models of cereals to phosphorus (P) fertilization on the major Finnish soil types by the means of a research synthesis and meta-analysis. We also calculated economically optimum P rates under different price combinations of P fertilizer (1-3 € kg -1 ) and cereal yields (100-300 € tn -1 ), for 1-year decision interval of P applications. Our material consisted of data on P fertilizer experiments conducted in Finland during the last 60 years on clay, coarse-textured mineral and organic soils, with variable soil test P (STP) status at the start of the experiments. The cereals cultivated were spring barley, oats, spring and winter wheat, and winter rye. The applied P rates ranged between 6 and 100 kg ha -1 . For low STP classes, Mitscherlich-type exponential models were appropriate for all soil groups, predicting 17-27% higher maximum yields when compared to the controls without added P. In contrast, for medium and high STP classes, the yield responses to increasing P rates were scattered around zero in most soils.Phosphorus fertilization had also negligible effect on 1,000-seed and test weights. On Finnish cereal farms, when P fertilizer is purchased, the present P rates allowed by the Agri-Environmental Programme are uneconomically high. It appears that P fertilization can be substantially reduced on majority of Finnish fields, or even omitted for years, without economic loss under current (2 € kg -1 ) or higher P fertilizer prices.

Phosphorus and Nitrogen Yield Response Models for Dynamic Bio-Economic Optimization: An Empirical Approach

“…Consequently, yield responses to P fertilization are probable for STP classes ranging from poor to fair, whereas the responses become improbable for STP classes ranging from satisfactory to excessive [12,45,46]. The applied ranges for the STP classes on coarse soils are here as follows: poor, 0-3; rather poor, 3-6; fair, 6-12; satisfactory, 12-20; good, 20-33; high, 33-50; excessive, >50 mg l −1 a −1 .…”

“…The data applied for the estimation of the yield response models included six separate datasets collected by Valkama et al [9,12] that described the measurements from Finnish P and N fertilizer field experiments of cereals for clay and coarse-textured soils. The standardization of the separate datasets is shown in Appendix A.…”

“…The standardization of the separate datasets is shown in Appendix A. Additional datasets for specifying the impact of STP on crop yield without added P fertilization were obtained from Saarela et al [11], since the information regarding this relationship was limited in the data obtained from Valkama et al [12]. Consequently, we were able to model the linkage between P response and STP, and the linkage between yield without added P and STP.…”

“…Multiple empirical models have been developed to separately capture yield response to N inputs [7][8][9], and to P inputs [10][11][12], and as a response to plant-available soil P [13][14][15]. Both the response to P fertilizer and soil P dynamics have been incorporated into an economic analysis of nutrient inputs [16,17].…”

“…Yield response modeling is a data-intensive process, as empirical data is needed for both building and validating the model [28]. In Finland, a long tradition of N and P fertilizer field experiments exists, motivated by the challenging agro-climatic production conditions due to the Nordic location and natural scarcity of P in the soil [9,11,12,[29][30][31]. As a result of these experiments, extensive empirical data for main cereals and different soil textures have been accumulated over five decades.…”