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FG Adriaanse

Sep 21

Leaching of different N Sources

By Nitrogen, Nitrogen Products, PLANT & SOIL NUTRITION No Comments

AFRIKAANS: Verskille in loging tussen Stikstofbronne Inorganic nitrogen (N) dissolved in groundwater could be lost for crop production through downward and sideway movements of groundwater, resulting in lower yields and profit margins above costs. Differences in leaching between N sources can effectively be utilized to reduce the risk of N leaching. N management practices such as application methods and timing could also contribute significantly to reductions in leaching losses. Basic scientific principles and case studies associated with severe losses in revenue were used to develop guidelines for combatting N leaching losses. The application of different N-sources results in one or a combination of nitrate-N, ammonium-N and urea-N dissolved in groundwater. The vertical movement of these forms of inorganic N in groundwater are displayed for a Sandy Loam soil in Figures 1 and for a Clay Soil in Figure 2. Ammonium-N resulted in very little leaching but large portions of the applied Nitrate-N en Urea-N moved with the groundwater to the level of water penetration. A little bit more Ammonium-N moved into the Sandy Loam soil compared to the Clay Soil but these amounts were insignificant for both soils. Larger portions of the applied Urea-N and Nitrate-N moved with the groundwater to the level of water penetration in the Sandy Loam soil compared to the Clay soil. Half of the LAN will show a similar response to Ammonium Sulphate and the other half similar to Calcium Nitrate since LAN consists of 50% Ammonium-N and 50% Nitrate-N. According to Figures 1 and 2 the immediate leaching potential of LAN is about 50% less than that of Urea. Ammonium-N could however over time be converted to leachable nitrate-N through the process of nitrification. The effect of LAN which was applied shortly before planting and at planting, followed by heavy downpours, resulting in severe leaching are presented in Figure 3. Severe N deficiencies in leaves and in the soil up to a depth of 60 cm have been confirmed with this case study. Yield loss as a result of N leaching was estimated between 7 and 8 ton/ha. Although risks of N-leaching are much less with LAN compared to Urea it is recommended that neither LAN nor urea be applied before planting on well drained soils. The effect of vertical as well as lateral movement of applied N due to excess rain is visible in Figure 4. N analysis in a strip over the rows to a depth of 750 mm was 39 kg/ha for A where the maize was yellow and stunted but 179 kg/ha where the maize was much more prolific and also greener. N analysis between the rows where N was not applied was 32 kg N/ha in the top 60 cm soil for both A and B. Variation in crop growth was therefore directly related to variation in soil N analysis over rows. This effect is often observed under high rainfall conditions on sandy soils, irrespective of time of N application. These symptoms are often incorrectly ascribed to poor fertilizer quality…

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Sep 14

Volatilization differences between N sources

By FERTILIZER PRODUCTS, Nitrogen, Nitrogen Products, PLANT & SOIL NUTRITION No Comments

Afrikaans Version: Verskille in vervlugtiging tussen Stikstofbronne Volatilization of applied nitrogen (N) is primarily in the form of ammonia (NH3), although losses in the form of atmospheric N (N2 and N2O) may also occur when soils are waterlogged. Ammonia is released from ammonium (NH4+) containing and forming fertilisers when there is insufficient soil water present in which the ammonia can dissolve. This will also occur when fertilisers are applied and left remaining on or close to the soil surface. Atmospheric nitrogen is formed from nitrate nitrogen (NO3–) when the topsoil is waterlogged and deprived of oxygen for long periods. Water scarcity rather than long periods of water logging are far more common in South Africa. This article therefore focusses on ammonia losses from applied fertilisers combined with factors affecting this process such as soil pH and temperature. The efficacies of urease inhibitors which delay the conversion of urea to ammonia together with other possible solutions for the problem of ammonia volatilization are also discussed. Soil pH significantly affects Ammonia volatilization losses. Ammonia losses from urea were increased by 18% over five soils when the pH was increased from 6.5 to 9.1 (Figure 1). Most losses occurred from urea, followed by DAP, Ammonium sulphate, MAP and LAN (Figure 1). The difference in ammonia volatilization between urea and LAN was 15% at a pH of 9.1 (Figure 1). The conversion of urea to ammonium and also DAP to ammonium are alkaline reactions. This explains why these products will lose more N in the form of ammonia than other products, forming or releasing similar quantities of ammonium with no increase in pH. High application rates of urea or DAP which would result in high concentrations on the soil surface will increase soil pH more and consequently more ammonia will be formed and lost. Nitrogen loss in the form of ammonia could be much higher than indicated in Figure 1. Du Preez & Burger (1986) showed ammonia losses of 55% which resulted from urea applications at a rate of 240 kg N/ha, on a soil containing 50% clay and which had an original pH (H2O) of 7.5. Botha & Pretorius (1988) showed ammonia losses of as much as 61% following urea applications at a rate of 83 kg N/ha on a soil with a clay content of 9.5% and a pH (H2O) of 7.9 after urea applications. Fenn & Miyamoto (1981) showed ammonia losses of 66% following urea surface applications on a soil with a pH (H2O) of 7.8. Ammonia losses are significantly affected by temperature. As temperatures increased from spring to mid-summer ammonia losses increased tremendously when using urea but also significantly with UAN (Figure 2). Ammonia losses from LAN however remained very low with increasing temperatures (Figure 2). Hoeft, et.al. (2000) stated that the potential for urease inhibitors to be effective would be best above 10° C. Urease inhibitors such as Agrotain, SKW Piesteritz and Hanfeng Evergreen delay the conversion of urea to ammonia and therefore also the release of ammonia. The…

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Sep 07

Differences in toxicity effects between LAN and urea

By FERTILIZER PRODUCTS, Nitrogen, Nitrogen Products, PLANT & SOIL NUTRITION No Comments

AFRIKAANS: Die verskil in toksisiteit tussen KAN en ureum Plant mixtures differ to a large extent in nitrogen (N) composition. Nitrate-N: ammonium-N ratios vary according to raw material contents. The optimum nitrate: ammonium-ratio is close to 3:1 while 100% ammonium-N could impair plant growth and yield (Adriaanse 1990). Some companies use urea-N as the primary N source in plant mixtures. Urea in close proximity to developing seedlings could impair or terminate growth. The band placement of certain N sources away from the plant mixture could also reduce yield. (Adriaanse 2012). Furthermore yield could be reduced by an overall excess of N in the soil. (Adriaanse and Schmidt, 2003). This article focuses on potential negative effects of band placed LAN and urea on germination, emergence, and production of maize and wheat. Plant Population Reductions The application of urea and ammonium nitrate at the same relatively high N rate may result in high seedling mortalities for urea compared to no mortalities for ammonium nitrate (Figure 1). These symptoms are often mistaken for genetically associated poor germination or poor seedling vigour. In addition these symptoms are often wrongly ascribed to damage caused by soil insects or meerkats. The band placement of 100 kg N/ha, 50 to 100 mm directly below maize seed at row widths of 1.5 m, resulted in a plant population loss of 4800 plants/ha with LAN compared to a loss of 13300 plants/ha when urea was used (Figure 2). Reductions in plant population were significantly more with urea compared to LAN at both 75 and 100 kg N/ha (Figure 2). This research illustrates relative differences in toxicity between urea and LAN under very specific conditions but does not imply that band placement of either of these N sources directly below the seed at low N rates is an acceptable practice under all conditions. Yield Loss Reductions in plant population due to the application of high N rates, is an indication of very severe N toxicity effects. Impairment of plant growth and yield loss could occur at much lower N concentrations. In another study where urea and LAN were band placed at planting, at a distance of 10 to 15 cm from the row, at a depth of 10 cm, the yield loss for urea compared to LAN was 20% at 100 kg/ha and 44% at 175 kg/ha (Adriaanse, 2012). Row widths were 1.5 m. Most farmers would probably not have been aware of the fact that urea toxicity had occurred.  The yield at 100 kg N/ha in the form of urea was 5 ton/ha which is in line with the yield potential of the area. No toxicity symptoms were observed on the plants, however a yield improvement of 20% at 100 kg N/ha could have been achieved had LAN been used under the same circumstances. Toxicity Symptoms Toxicity symptoms associated with high rates of both urea and LAN applications would probably result in yield loss due to high N concentrations in the soil. In contrast, scorching of leaves associated with spreading of N sources over leaf…

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Aug 31

El Nino or La Nina – manage nitrogen (N) in the soil to ensure maximum maize yield, maximum profit and minimum risk.

By Nitrogen, Nitrogen Products No Comments

AFRIKAANS: El Nino of La Nina – bestuur stikstof (N) in die grond om maksimum mielieopbrengs, maksimum wins en minimum risiko te verseker The quantity of measurable inorganic N that should be in the soil throughout the growing period for maximum yield does not differ between El Nino (dry) or La Nina (wet) or average rainfall seasons but the actual yield, profitability and risk will differ to a large extent between these conditions. The quantity of N that is taken up and utilized by the crop will also differ largely between dry and wet seasons. For this reason it can be expected that more N will be applied during a wet season to maintain the quantity of N in the soil. It can also be expected that more N will be left over in the soil after a dry season which can effectively be utilized during the next season. The management of a threshold value for N in the soil for every season will effectively result in fertilization according to obtained yield and N removal from the soil over seasons. N-losses and N-toxicity effects will however very strongly be affected by an under or over supply of rain. Apart from soil N-measurements, choice of N-source and N-management practices can effectively be used to reduce these negative effects. El Nino conditions also coincide with high temperatures resulting in volatilization losses from ammonia forming products such as urea. Ammonia losses can result from surface applications as well as soil incorporated applications when the topsoil dries out. Ammonia released in close proximity of plant roots will be toxic under dry conditions. Urease inhibitors such as NBPT will effectively reduce or delay volatilization and toxicity from urea but will not eliminate these effects. Almost no N will volatilize from LAN even at high temperatures. LAN will only be moderately toxic at high concentrations. The band placement of high concentrations ammonia forming N-sources at planting but even before plating should therefore be avoided. La Nina conditions also coincides with heavy downpours over short periods resulting in N-leaching in well drain soils or water logging in poorly drained soils. Urea-N and nitrate-N are equally leachable but due to the fact that nitrate uptake is much quicker it will effectively leach much less than urea. Ammonium-N does not leach significantly and is also taken up much quicker than urea-N. LAN will therefore also leach much less than urea. Due to the possible risk of leaching pre-plant applications should rather be avoided and multiple post-plant topdressings considered. N is not taken up effectively in soils that are waterlogged for prolonged periods. Oxygen is required for N-uptake but also for the nitrification process. Consequently high levels of ammonium-N and nitrite-N, which are toxic, will accumulate. Nitrate-N dissolved in soil water near the soil surface will be converted to atmospheric N through the denitrification process and lost. Vertical or lateral drainage of soils should improve this condition.  

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