Nutrient Omission Plot Technique

The nutrient omission plot technique is a tool for determining the amount of fertilizer N, P, and K required for attaining a yield target (see photo). In this technique, four 25m² plots with the following treatments are placed in a farmer’s field:

1.      Full fertilization: NPK applied

2.      N omission (–N): No N applied, PK applied

3.      P omission (–P): No P applied, NK applied

4.      K omission (–K): No K applied, NP applied

Fertilizer N, P, and K are applied at sufficiently high rates to ensure that yield is not limited by an insufficient supply of the added nutrients. Grain yield in the plot with full fertilization and relatively good crop management can be used to estimate an attainable yield target. Nutrient-limited yields are determined from plots in which the nutrient of interest is not added. For example, the N-limited yield is determined in an N omission plot receiving no N fertilizer but sufficient P and K to ensure that they do not limit yield. The K-limited yield is determined in a K omission plot receiving no K fertilizer but a sufficient supply of other nutrients.

The difference in grain yields between a fully fertilized plot and an N omission plot illustrates the deficit between the crop demand for N and indigenous supply of N, which must be met by fertilizers. Similarly, the difference in grain yields between a fully fertilized plot and a K omission plot illustrates the deficit between the crop demand for K and indigenous supply of K, which must be met by fertilizers.

A nutrient omission plot study conducted in a farmer’s field. (Photo by S. Abdulrachman)