i grow pea plants in a field and harvests them, but leaves the roots. why do i not need fertilizers next year?

Question

year 11 science

Answer 1

Pea plants are legumes. They have nodules on their roots that are homes for nitrogen-fixing bacteria. These bacteria take nitrogen from the air and change the nitrogen gas into nitrogen compounds that the plants can use. In fact, the bacteria convert more nitrogen gas than the plants actually use. Leaving the roots in the soil lets the extra nitrogen compounds stay in the soil for next year's crop. Good idea.

Answer 2

Peas are legumes so are also in a symbiosis with nitrogen fixing rhizobia bacteria. These bacteria live in root nodules where oxygen is excluded so they can carry out nitrogen fixation.
These plants use phosphorus & other nutrients even though they provide nitrogen. For optimal growth and yield they may need some fertilizer and a pH test to ensure the soil is pH 6-6.7 for peas. Soil is most fertile for a plant when in the pH range that plant requires. There are twelve nutrients that plants acquire from the soil besides nitrogen. If even one of these nutrients is low then plant growth will be slower. All nutrients are effected by the soil pH.
pH effects on soil
http://www.extension.umn.edu/distribution/horticulture/components/1731-03.html
Plant Nutrients http://www.agr.state.nc.us/cyber/kidswrld/plant/nutrient.htm

Answer 3

The plants are high in nitrogen, so they break down and fertilize the soil.