The environmental impact of fertilizer use is lessened by all those measures that improve nutrient use efficiency (NUE), specifically that of nitrogen, i.e. increasing the uptake of nutrients by plants and thus leaving less in the soil at risk to loss to the environment. The environmental aspects of controlled-release fertilizers have been investigated by Shaviv and Mikkelsen (1993b). Comparing several types of polymer-coated urea, Shaviv (1995) found that increasing N-use efficiency and lowering their impact on the environment can be critically affected by the release characteristics of the amended urea in relation to the pattern of demand for N by the crop.
With slow- and controlled-release fertilizers, the best agronomic and environmental results are obtained with products that do not have the so-called ‘burst effect’ and
‘tailing effect’ (Shaviv, 1995, 2005). Large yields and, at the same time, minimal adverse effects on the environment can be expected when the release pattern of nutrients from slow- and controlled-release fertilizers are synchronized to the crop’s nutrient uptake pattern. Consequently, for good N fertilizer management, much detailed information is required about the release pattern in water and in the soil. In addition to the adverse
‘burst effect’ on excess nutrient release, any ‘tailing effect’ after harvest of the fertilized crop must be studied to assess the positive effects of controlled-release fertilizers on the environment.
According to Shaviv (2005) an effective assessment must include:
nutrient release characteristics and mechanisms,
the effects of environmental factors (temperature, moisture, aeration, bio-activity, root exudates, soil type, etc.) on the release and the nutrient use efficiency, and
the plant’s demand for nutrients under a range of agricultural conditions.
This information is important, because encapsulated controlled-release fertilizers are products designed to solve a number of specific technical and environmental problems in agriculture and horticulture, landscape management and gardening. Users who prefer coated fertilizers because of the savings in labour, should also be aware of the environmental benefits through their nutrient release properties.
Dou and Alva (1998) studied the effect of several controlled-release fertilizers compared to urea on citrus rootstock seedlings in a sandy soil. They demonstrated that, for a given N application rate, the total N uptake by the seedlings was greater for controlled-release fertilizers than for urea and they concluded that N losses would
therefore be less when using controlled-release fertilizers as an N source compared to a soluble N fertilizer.
With intensive agriculture in Japan, N fertilizer commonly makes the greatest contribution to crop production while it has the highest potential for environmental degradation (Shoji and Kanno (1993) and Shoji (1999, 2005). Shoji and Mae (1984) considered that to minimize nitrate pollution but optimise yield in a given farming system, it is necessary to maximize N-use efficiency as shown in Table 21. Maximizing NUE requires programmed fertilization using controlled-release fertilizers (e.g. such as Meister®), best fertilizer placement, and soil conditions favourable to plant growth.
Innovative farming systems as well as using controlled-release fertilizers contribute to the improvement of the agro-environment (Shoji, 1995, 2005). For example, appropriate controlled-release fertilizers in no-till rice culture can effectively improve the water, atmospheric and biological environments of rice fields.
Table 21. Minimizing nutrient pollution by maximizing nitrogen use efficiency: Case study in a rice field in North-east Japan on NUE (Shoji, 2005).
Case NUE N rate N rate
reduction N uptake
by rice Max. potential fert. pollution
% kg N/ha % kg N/ha kg N/ha
1 30 100 0 30 70
2 80 40 60 32 8
Notes:
30% NUE: average data of conventional fertilizer basal application 80% NUE: highest data of Meister application
Masuda et al. (2003) studied the decrease in nitrate leaching when polymer-coated N fertilizers were applied to sugarcane and showed that N fertilizer use could be decreased by about 40% without causing a reduction in sugar yield. Nitrogen absorption was estimated at 57.7% and 90.9% with conventional and controlled-release fertilizers, respectively.
Zhang (2007) reported the results from experiments, demonstrations and advisory work on more than twenty crops over several years at the Shandong Agricultural University. Crop yields were larger when using a controlled-release fertilizer, than when using conventional fertilizers although the amount of nutrient applied was a third or a half less with the controlled-release fertilizer. The quality of the crops and food products was also improved. In addition to the increase in N-use efficiency, N volatilization and leaching losses were considerably reduced through the application of controlled-release fertilizers. Zhang (2007) concluded that, in regions where there was excess application of conventional fertilizers, the increase in severe non-point pollution could be reduced considerably by using controlled-release fertilizers. Ma et al. (2007) found in experiments on the main soil types in Shandong Province, that ammonia volatilization is influenced by soil type and that N losses from conventional fertilizers
are greater than those from controlled-release fertilizers. Zhang et al. (2001) found in N leaching experiments with various fertilizers in soil columns that, in addition to other positive aspects, controlled-release fertilizers had less influence on changes of the soil pH than conventional fertilizers. Figure 20. is the result of investigations with ESN showing the reduction in nitrate leaching losses.
The following graph (Figure 21) shows how the polymer-coated urea ESN reduces ammonia volatilization.
The reduction of nitrate leaching and ammonia volatilization through the use of ESN is also reported by Blaylock (2010). Halvorson and Del Grosso (2010) have found that using ESN also results in reduced N2O fluxes. However, significant results have only been obtained in no-till crop rotations with maize (reduction of 49%); whereas results with conventional tillage maize have been negligible.
Various agricultural research centers in Japan have demonstrated that for rice, maize, sugarcane, potatoes, tea and numerous vegetables nutrient application rates could significantly be reduced (by 20 to 60%) when slow- or controlled-release fertilizers are applied, without sacrificing yield. In addition, only one single basal application is necessary (Tachibana, 2007). Shoji et al. (2001) compared a polyolefin-coated urea with nitrification inhibitor and unamended urea on flood irrigated barley, center-
Figure 20. Measurement of ESN effect on N leaching losses in Piketon (Ohio) in 2003 (Adapted from Agrium, 2005).
Inorganic N in leachate from 100- x 30-foot lysimeters. Calculated from total water volume and N concentration (Islam, Ohio State University).
February March May June July August
Total cumulative N loss (lb N/ac)Total monthly precipiation (in inches) 0 2 4 6
0 4 8 8 10
April
ESN 30 Urea 45 UAN 45
Control ESN 45
N applied April 4 at 30 or 45 lbs N/a on winter wheat
pivot irrigated potato and maize grown in a large-scale lysimeter, all on different soils.
Nitrous oxide emissions from the controlled-release fertilizer plots were almost one third of those with urea, and N recovery was almost twice that achieved with urea. The authors concluded that the contribution of controlled-release fertilizers and nitrification inhibitors to air and water quality conservation is basically due to greater NUE and reduced N fertilization rates.
Alva and Tucker (1993) and Alva et al. (1993) concluded from experiments in a citrus orchard in Florida that there is no adverse affect on the growth of young citrus trees when the frequency and rate of N application is reduced by using polyolefin-coated controlled-release fertilizers and that nitrate leaching can be minimized also.