A certified organic grower plans to grow a crop that requires the application of

Question

A certified organic grower plans to grow a crop that requires the application of 120 kg of plant-available N/ha and 20 kg/ha of P. She has a source of compost that contains 1.5% total N (w/10% of this available in the first year) and 1.1% total P (w/80% of this available in the first year).

Assuming her soil has a low P soil test level, how much compost should she apply to provide the needed N and P?

If her soil is already optimal in P, how can she provide the needed amounts of both Na and P without causing further P buildup?

Explanation / Answer

Given:

120 kg N/ha

20 kg P/ha

Nitrogen increases plant height, panicle number, leaf size, spikelet number, and number of filled spikelets, which largely determine the yield capacity of a rice plant. Panicle number is largely influenced by the number of tillers that develop during the vegetative stage. Spikelet number and number of filled spikelets are largely determined in the reproductive stage.

The early N application (65 to 100 percent of the total N rate) should be applied as an ammonium N (NH4+) source onto dry soil, immediately prior to flooding at around the 4- to 5-leaf growth stage. There is not an exact time to apply early N, but actually a window of a couple of weeks that the early N can be applied. Once the early N is applied, flooding should be completed as quickly as possible, preferably within five days of the N application. The flood incorporates the N fertilizer into the soil where it is protected against losses via ammonia volatilization and/or nitrification/denitrification as long as a flood is maintained.

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