1. Abera K (2013) Growth, productivity and nitrogen use efficiency of maize (Zea mays L.) as influenced by rate and time of nitrogen fertilizer application in Haramaya District, Eastern Ethiopia
2. Amsal T, Tanner DG (2001) Effects of fertilizer application on N and P uptake, recovery and use efficiency of bread wheat grown on two soil types in central Ethiopia. Eth J Nat Res 3:219–244
3. Brady NC, Weil RR (2000) Elements of the nature and properties of soils, vol 12. Printice-Hall Inc, Upper Saddle River
4. Fageria NK (2007) Yield physiology of rice. J Plant Nutr 30:843–879
5. Fageria NK, Baligar VC, Jones CA (1997) Growth and mineral nutrition of field crops. Mercel Dekker Inc., New York