摘要
Environmentally smart nitrogen(ESN)is polymer coated urea that is designed to release N in synchrony with crop requirements.Research on ESN was initiated in field crops in Ontario,Canada in 2006,initially on timothy,spring wheat and winter wheat and later(till date)on bromegrass,grass mixtures(timothy,bromegrass,orchardgrass),other forages(barley,silage corn,oat,MasterGraze corn and sorghum Sudangrass)and canola.In winter wheat,in three out of six years ESN gave^0.6 MT/ha higher grain yield than urea.In spring wheat,in a relatively warm year with well-distributed rainfall,ESN produced 1 MT/ha higher grain yield than urea;averaged over three years,two-thirds N from urea and one-third N from ESN could be recommended.Two-thirds N from urea and one-third N from ESN gave^0.75 MT/ha extra seed yield as compared to urea alone at 180 kg N/ha in canola during 2016 to 2018.The entire N in winter/spring wheat could be applied in seed rows at seeding as ESN without any detrimental effect.The highest barley forage yields were recorded by urea at 50 kg N/ha+ESN at 20 kg N/ha which produced 1.2 MT/ha more forage yield than urea at 70 kg N/ha.Partial substitution of N from urea with ESN improved forage dry matter yield of timothy and MasterGraze corn.In MasterGraze corn 100 kg N/ha from urea+ESN(3:1 on N basis)equaled that with urea at 150 kg N/ha in dry matter yield,%protein and relative feed value(RFV),but not in silage corn and sorghum Sudangrass.At equal rates of N,single/fall application of ESN in timothy and bromegrass gave equal yield to urea applied in two splits in spring/summer.Spring wheat grain yields were the same with fall/spring application of ESN.ESN/urea+ESN(3:1 on N basis)increased the grain/forage protein content in almost all crops by 1%-2%points at an extra cost of only$6.0-10.5/ha(with urea+ESN in 3:1 ratio on N basis).The results indicate that ESN could improve both crop yields and quality,make better use of N/or increase N-use efficiency.The paper summarizes results from over 10 years and the results could be applicable globally under situations of high N losses from readily available N sources such as urea.
