Nitrogen is one tricky element to study in fields due to soil variability and the fact that N is very mobile. Experienced folks have told me that using some models, they have not been able to get realistic findings, close to actual. How can one make better simualtions of N response in cereals say in a trial of 3 seasons?
studying N dynamics is not easy, as you say. However,if you can easily have N analyses of plant tissue, you can follow the growth and total N uptake (in kg ha-1) in some reference cereals (depending on where you are and what you cultivate, such as wheat, barley and oat or corn and milet or rice and so on).
Usuall, cereals have a high N demand, so the available N will correlate with the total N influx (in high density stands).
In addition, if you can use the isotopic 15N (as fertilizer, for scientific purposes), you can also separate the fertilizer from the soil N pool effect.
Finally, you can study N influx in plants or crops in different conditions (such as water availability, P availability, etc.) in order to achieve information about the effects of different agronomic/environmental condition on N dynamics.
did you think of using optical sensors such as a SPAD or greenseeker?
A spad (http://www.geneq.com/catalog/en/spad-502.html) is not really good for predicting but this is harldy possible in any case.
A greenseeker has more potential (see e.g http://www.plantstress.com/methods/Greenseeker.PDF)
If you want to use simulation models, it would be necessary to find out first why existing models fail at your site. Many crop models do work in the tropics, however, they have been mostly developed in temperate regions where soils are negatively charged. In positively charged soils some model functionalities may not apply. A simple N treatment trial over three seasons with simultaneous crop and soil observations (dry weight, tissue N%, grain N%, soil mineral N, soil moisture at several dates during the growing season) will give you a good data basis to evaluate several models. The critical N concentration of cereals seems quite universal across varieties, so you will learn from your data how the crop responds to N movement and availability in the soil. The crop models will then tell you how N availability interacts with other crop-growth influencing factors.
Sergio Saia, many thanks for the response. I am working on rice in upland soils.I will look at some models on N. I agree with you because isotopic N will surely track the applied N in the system
Class Nendel, thank you. The element of dates is what had not rang in my mind. I want to use for crop model for N simulations to explain scenarios on a wider scale after trial.
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