Comparing Extraction and Quantity/Intensity Based Recommendations for Nitrogen, Phosphorus and Potassium Recommendation

  •  Nqaba Nongqwenga    
  •  Albert Modi    


Conventional, extraction based fertilizer recommendations for phosphorus and potassium have been shown to lack mechanistic basis, thus unreliable. This has led to an urgent need for the development and evaluation of accurate and consistent phosphorus and potassium recommendations approaches with mechanistic basis. Also it has been shown that integrating nitrogen mineralization on nitrogen recommendations, has a potential of improving nitrogen recommendations. We established two parallel pot trial studies with the objective of comparing between extraction based fertilizer recommendations with alternative strategies. The first study was to compare the effect of integrating nitrogen mineralization on N recommendations. Second pot experiment in addition to N being recommended after integrating N mineralization; P and K were also recommended with an alternative strategy, which was derived from quantity/intensity relations. No negative impacts were observed on crop growth and nutrient uptake due to the integration of mineralizable nitrogen, despite nitrogen amounts being lower compared to treatments where N was applied without adjusting for mineralizable N. The same was true for the second pot trial, P and N recommended by conventional approach were higher, yet the crop response was not concurrently improved by higher rates. Potassium rates recommended by alternative strategy were higher and this was concurrent with potassium uptake. We therefore concluded, that this NPK recommendation experimental approach (NePeKe) is superior to its conventional counterpart (NcPcKc). Hence, more reliable recommendations can be developed using this approach and this might reduce environmental footprint of agro-ecosystems, and reduce input cost for farmers where warranted.

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