You can look up journals or subject areas using this web site: http://www.bioxbio.com/if/ or others like it.
Plant And Soil is 3.235
Biology And Fertility Of Soils is 3.396
Advances In Agronomy is 5.021
You will have to see if what you want to publish fits these journals. My experience is that agricultural journals have a relatively low impact factor. See: http://www.bioxbio.com/if/subject/agriculture-1.html
Although not having an impact factor, Frontiers is a growing (and serious) open access publisher that has a Plant nutrition section.
http://www.frontiersin.org/Plant_Nutrition
Note that their is growing criticism against judging the quality of a paper (or worse, a researcher) according to the IF. The meaning of the IF should be interpreted with care, and there are documented cases of IF hacking. Wikipedia has a good review of IF criticisms. https://en.wikipedia.org/wiki/Impact_factor#Criticisms
If the work is an innovative one and interesting results have been obtained, then why are you not targeting for 'Nature'? Of course, you will find very good other journals also viz. Journal of Plant Nutrition and Soil Science, Nutrient Cycling in Agroecosystem, Plant and Soil, Soil Science and Plant Nutrition, 'Agronomy Journal' as others suggested. If your work is related to biology and ecology, then you may opt for journals like Current Biology, Global Change Biology, Ecology, Acta Physiologia, Journal of Agricultural Sciences (Cambridge), Annals of Botany etc.
Anyway, it is not understood why this boundary of IF 5.00?