1. Ketterings QM, Czymmek KJ, Klausner SD (2003) Phosphorus guidelines for field crops in New York. Second Release, Dept crop and soil sciences, Cornell Univ.
http://nmsp.cals.cornell.edu/guidelines/nutrientguide.html
. Verified 21 Jan 2018
2. Jokela B, Magdoff F, Bartlett R, Bosworth S, Ross D (2004) Nutrient recommendations for field crops in Vermont. Plant and Soil Science Dept., Univ. Vermont.
http://pss.uvm.edu/ag_testing/VTNutrientRecFieldCrops1390.pdf
. Verified 31 Jan 2018
3. McFarland M, Devlin D, Koenig R, Osmond D (2006) Comparison of land grant university soil test recommendations for nitrogen, phosphorus and potassium.
https://scisoc.confex.com/crops/2006am/techprogram/P23731.HTM
. Verified 31 Jan 2018
4. Sims JT (2009) Soil test phosphorus: Principles and methods. In: Kovar JL, Pierzynski GM (eds) Methods of phosphorus analysis for soils, sediments, residuals and waters, 2nd edn. Southern Cooperative Series bulletin No. 408. Virginia Tech University, Blacksburg, pp 9–19
5. Dodd RJ, Sharpley AN (2015) Recognizing the role of soil organic phosphorus in soil fertility and water quality. Resour Consev Recycl 105B:282–293