A well-planned experiment design should be employed to impose different levels of N treatment for assessing plants responses in soil. Given my academic and field experience, for example in work with baby corn and Capsicum annuum under different doses of nitrogen, the first is to choose uniform plots or pots, and they have to be prepared with the same type of soil and minimum fertility level. Based on the available resources and space, I would take the experimental units and divide them into treatments, e.g., control (0 N), low, medium and high N levels in a RCBD or CRD laying appropriate replication to support meaningful statistical inferences. According to the crop nutrient requirement and soil test results, I would calculate the nitrogen needed, and then apply them via urea or other N sources at certain growth stages (basal & top dressing). Previous experience in varietal and multi-location trials of Wheat, Soybean, and work on economic analysis and the effect of nitrogen on crop yield makes me suitable candidate to monitor the growth, yield, and Ana application of physiology responses. Also, my proficiency of data management and analysis by using MS Excel, R and Python will help me to interpret the treatment effects to draw meaningful conclusions concerning the plant-soil-nitrogen interaction.

For a good investigation into the reaction of chosen plants to varying levels of nitrogen (N) in soils, an excellently designed test with regulated N treatments is fundamental.

Start with identifying the target plant species and having several levels of N treatments defined, e.g., a control (low N or no N) and diverse concentrations (e.g., 50, 100, and 150 kg N/ha) to provide dose-response measures.

The source of nitrogen should be selected according to the study's objectives—typical fertilizers used are ammonium nitrate (NH₄NO₃), urea, or organic materials such as compost.

For pot experiments, dissolve the N fertilizer in water for even application or incorporate it into the soil before planting to have the same soil characteristics among replicates.

In field experiments, granular N may be broadcast or band-applied close to the roots of the plants. Important growth parameters like plant height, biomass, chlorophyll content, and root growth should be measured over time, in addition to post-harvest tissue and soil N analysis to assess uptake and residual effects.

Accurate replication (3–5 replicates per treatment) and randomization are important to achieve statistical significance, and data must be analyzed with ANOVA or regression models to ascertain significant differences among treatments.

Aspects such as N leaching, changes in soil pH, and time of application should also be taken into account to ensure experimental precision. This methodical procedure enables an optimum evaluation of the impact of differences in N on plant growth and soil health.

You are asked to test the soil nitrogen content using standard procedures. The critical limit of Nitrogen content in the soil is 480kg/ha high level of Nitrogen content, so no need to apply. Apply based on the Nitrogen already available in the soil. Choose the right composition of manure and fertilizers. Note: the critical limit may vary depending upon the soil series; therefore, consider the soil series and its physico-chemical characteristics.