|Abstract or Summary
- Ammonia (NH₃) volatilization can result in a substantial amount of surface applied nitrogen (N) being lost into the atmosphere, making it an environmental pollutant as well as reducing plant-available N. However, N can also be easily lost from the soil through leaching,
and nitrous oxide (NO₂). Enhanced efficiency N fertilizers and cultural practices can be used to reduce N pollution and keep N plant-available. The use of these fertilizers and practices has not
been examined in the Columbia Basin in Oregon. The objectives of this study were to: (i) examine the effective irrigation rate needed to reduce loss from volatilization from urea, (ii) examine the effectiveness of urease inhibitors in minimizing NH₃ loss, measure interactions between inhibitors and irrigation, and measure hydrolysis rates with inhibitors, and (iii) examine if enhanced efficiency N fertilizers could maintain or increase potato yields, whether petiole NO₃ accurately reflected plant N with these products, and if they release N according to plant uptake.
In the first study, irrigation rates of 0.0 to 22 mm were applied over surface applied urea using a center pivot irrigation system on a wheat field. Ammonia was collected from each plot using the modified passive flux method for 23 days after application (DAA). Cumulative loss of N as NH₃ ranged from 3 to 67 kg N acre⁻¹, with the application of 8 mm irrigation reducing loss to 19 kg N ha⁻¹. Peak NH₃ loss occurred between 2 and 8 DAA. The reduction of N loss by 90% was
obtained through the application of 15 mm irrigation. Increased wheat N concentration was associated with decreased NH₃ loss.
The second study consisted of recording NH₃ loss on a grass seed field from urea, ammonium sulfate, and Agrotain-treated urea. This study also involved recording NH₃ loss on a wheat field from urea, Agrotain, and an organo acid complex containing co-polymers (OAC) treated urea at irrigation rates of 0.0, 1.25, and 7.6-mm. Volatilization loss was measured using the modified passive flux method. Urea, Agrotain, and OAC were incubated with soil at three temperatures to measure hydrolysis rates. In the grass seed study Agrotain reduced N loss from
NH₃ by 71.8% compared to urea, while ammonium sulfate reduced loss by 60.4% compared to urea. In the wheat study, Agrotain lost 5.72 to 6.24% N applied at the 0.00 and 1.25-mm irrigation rate, compared to 53.44% to 60.05% N applied for urea and OAC. With the application
of 7.6-mm irrigation, all loss declined with rates of 17.31, 8.11, and 3.17 N applied for urea, OAC, and Agrotain, respectively. Agrotain also decreased urease activity in the wheat field compared
to urea and OAC. In incubation, Agrotain delayed complete hydrolysis by 7 days at 26.7°C, 15 days at 16.6°C, and 49 days at 4.4°C compared to urea and OAC. Urea and OAC had similar hydrolysis rates at all temperatures. The use of an effective urease inhibitor, such as Agrotain, can be used to delay hydrolysis and reduce NH₃ loss if urea cannot be incorporated.
In the final study, enhanced efficiency N fertilizers were applied to Russet Norkota and Russet Burbank potatoes to compare yield and quality with grower standard practices (GSP). Plant N samples were taken from the third year to examine whether petiole nitrate accurately reflected plant N with these products. An incubation of all products for 104 DAA was performed at 4.4°C, 16.6°C, and 26.7°C to measure ammonium (NH₄) and nitrate (NO₃) formation. Similar
yields were measured for both years with Russet Norkota. All N treatments were similar, even the 80% GSP, suggesting that N rates were in excess of crop need, thereby reducing sensitivity of
N-inhibitor measurements. Reduced yields were measured in two years for Russet Burbank when enhanced efficiency fertilizers were applied compared to 100% GSP. Enhanced efficiency fertilizers maintained yields for one year compared to 100% GSP. Yields with N treatments were usually similar to the 80% GSP, suggesting that N release was not matched with N uptake. In the incubation study, all products except Nutrisphere-N (NSN) were able to delay N release compared to urea. Each product was influenced by temperature, with decreased temperature resulting in a longer delay in conversion of urea to NH₄ and conversion of NH₄ to NO₃ N. Nitamin and N-fusion had only 100% N available at 26.7°C after 104 day. Enhanced efficiency N fertilizers cannot sustain or increase yields on a yearly basis, making their incorporation into Columbia Basin potato production impracticable based on economics. Enhanced efficiency N fertilizers and cultural practices can reduce N loss. However, a reduction in N loss does not always lead to sustained or increased yields. The use of cultural
practices can be implemented with minimal expense; however, the fertilizers must present an economical benefit, either as increased yield or a N reduction to be viable in most cropping systems.