1. Urea — soon to be the principal dry source of fertilizer nitrogen in North America;Beaton;Agron. Abstr.,1976
2. Effect of nitrogen on the availability of soil and fertilizer phosphorus to plants;Grunes;Adv. Agron.,1959
3. A Model to Determine N, P and K Fertilization Recommendations under Field Conditions;Hadas;Agric. Res. Organ., Inst. Soil and Water, Pamphlet No. 217,1979
4. The water-culture method for growing plants without soil;Hoagland;Calif. Agric. Exp. Stn. Circ.,1950
5. Ionic balance in different tissues of the tomato plant in relation to nitrate, urea or ammonium nutrition;Kirkby;Plant Physiol.,1967