ChileanJAR

The response to three fertilizer formulations: N (ammonium nitrate), NP (N + triple superphosphate) and NPKS (NP + potassium sulfate) was determined in 70 soil samples of the Biobio province in a pot experiment. All the samples were superficial except four that were taken below 20 cm. It was confirmed that the main nutritive defienciencies were P, K and S, as had been estalished with the minus one element technique used in Part XX of the present series. ln general, this response can be predicted from the characteristic fertility Unes of each sample. The use of N alone does not raise the fertility of the soil to the level defined by the P fertility Une. With NP, yield is raised to the level defined by the K fertility line. Fertilizatión with NPKS will optimize the fertility of most soils in the Biobo province. Nevertheless there are some soils with severe deficiency of Mg or microelements, or of both at the same time, in which that fertilization is not adequate. Under such conditions it will be necessary to complement the NPKS fertilization with Mg or microelement, but itwill be necessary to determine the specific microelements missing. In some soils it is apparently possible to movilize non exchangeable K with the application of ammonium nitrate. This characteristic has an agronomic importance, because it establishes a limit to the use of ammoniacal fertilizers. The participation of the biomass in the fertility of the soil is admitted, and it would affect mainly N, P and S. A thermic activation of the mesophique and thermofique populations, acting on the organic fraction of the soil through mineralization and inmovilization processes, may be possible.