N-P-K experiments with potatoes in the lower St. Lawrence region of Quebec

Summary

The effects on potato yields and soil fertility of 27 different combinations of the main fertilizer elements (N, P, and K at 0, 40, and 80 pounds per acre) were compared in an eight-year 3³ factorial experiment on Saint-André gravelly loam soil in the Lower St. Lawrence valley.

The results indicate that applications of nitrogen should not exceed 60 or 70 pounds per acre, otherwise they will lead to loss of quality.

Additional amounts of phosphorus and potassium supplied in the form of fertilizer to potato fields which were already sufficiently rich in these elements were not completely utilized by the plants. Soil analyses revealed that, on the average, 27% of the phosphorus and 40% of the potassium accumulated in the soil and was available to other crops in the rotation.

Potatoes appear to derive a considerable part of the phosphorus and potassium they need from reserves in the soil, especially those resulting from the use of conventional fertilizer formulas such as 5-10-13 and 8-16-16 and on intensively farmed land.

Nevertheless, a superfluous supply of P and K seems necessary if high yields are desired. Therefore, in common with a number of authors (3, 5, 12, 13, 15) we would recommend application of these two elements even though such requirements are not clearly justified according to soil analysis. Ratios for N:P₂O₅:K₂O of 1:1 1/2: 1 or 1:2:1 are suggested. This balance would be satisfied by the formula 8-16-8, which seems to us to be quite suitable for fertilizing potatoes under conditions similar to those encountered in eastern Quebec. The rate of application might range from 800 to 1200 pounds per acre.

Resumen

Estas investigaciones demuestran que la dosis de nitrógeno no debe exceder de 60 a 70 libras por acre, pues de lo contrario, se provoca una pérdida de calidad en la patata.

Siendo el suelo suficientemente rico en fósforo y en potasio, las aportaciones artificiales de estos dos elementos no fueron enteramente utilizadas por las plantas. Se ha encontrado, gracias a los análisis del suelo, que 27% del fósforo y 40% del potasio se acumulaban permaneciendo disponibles.

Parece, sin embargo, que un aprovisionamiento superabundante de P y de K sea un mal necesario si se desean obtener rendimientos elevados. Por ello se ha recomendado, al igual que otros autores, (3, 5, 12, 13, 15) una determinada cantidad de P y de K, aunque las necesidades no estén plenamente justificadas. Se preconiza el equilibrio (N:P₂O₅:K₂O) 1-1 1/2-1 o bien 1-2-1 ; lo cual equivale a la utilización de la formula 8-16-8, que nos parece enteramente adecuada para la fertilización de las patatas en condiciones parecidas a las que se encuentran en el este de la provincia de Quebec. La dosis puede variar entre 800 y 1200 libras por acre.