There all kinds of ways and amounts to fertilize melons and each of you has their own “special mix” that works just right for you. Even though each of you does it different there is some interesting information about amounts based on growth that might be useful. Dr. Don Maynard, University of Florida edited the Watermelon Production Guide for Florida and in it he lists a fertigation schedule for a seeded mulched watermelon crop. I am asked occasionally how much nitrogen should I be applying and the answer is “it depends.” I use the number 120#’s as the total N that you will probably apply in the season minus what you’ve already put out, say 40#’s which leaves 80#’s to apply in 8 weeks or 10#’s per week. This is pretty simply but it doesn’t take into account that sometimes the plants need more nitrogen than at other times. Dr. Maynard includes this schedule which takes into account the plant needs.This chart assumes that you will apply 120#’s of total N and that 20% was already put down as a starter N before planting. Assuming it takes 15 weeks from planting a seed to final harvest then you just follow along with each week applying the amount of N recommended per day for seven days then go to the next week. They recommend applying N through the drip each day but not many producers do that so just use the chart to calculate how much N you need and when you need it. He also adds that if you are using transplants then start on week 3 just shortly after you set out the plants.
You can see that in weeks 9 and 10 the plants are really using the nitrogen and after that the plants begin to concentrate on making fruit instead of plant growth so nitrogen is used less. Those big plants also have stored nitrogen in the leaves which they can use for maintenance and fruit giving you a safety net. We see the same kind of response in most field crops like corn where we would put most of the nitrogen out before tasseling to insure it is available when the ears are made.