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PLANT & SOIL NUTRITION

Plant nutrients

Nov 19

USE OF FERTILIZER NITROGEN ON INTENSIVE PASTURES

By Nitrogen, Nitrogen Products No Comments

Afrikaans: Stikstofbemesting vir Intensiewe Weidingproduksie Nitrogen (N) is the nutrient taken up in largest quantities by pasture plants from the soil.  Its availability, together with temperature and moisture supply, are usually the major factors determining the productivity of pastures. Responses of grasses to applied N The responses of pastures to fertilizer N have been studied in scores of research trials both locally and overseas.  In South African research, the major focus has been on the N requirements of ryegrasses, kikuyu and Eragrostis curvula (weeping lovegrass), with limited work being carried out on other species such as cocksfoot, fescue and Digitaria eriantha (Smuts fingergrass).  For the relation between grass DM (dry matter) yield and fertilizer N applied, a characteristic response curve is obtained, an example of which is presented in Figure 1. When N is applied there is usually an initial near-linear response (A in Fig. 1), a phase of sharply diminishing response (B) and a point (C) beyond which N has little or no effect on yield.  The amount of DM produced for each kilogram of N applied within zone A depends largely on the species under consideration, the frequency of defoliation and growth conditions.  Tropical grasses generally produce more DM per unit of N than do temperate grasses.  In field trials, Eragrostis curvula, for example, has produced up to 60 kg DM per kg N applied, but irrigated Italian ryegrass only between 25 and 34 kg DM per kg N applied.  In the United Kingdom, perennial ryegrass produced an average of 23 kg DM/kg N over an N application range of 0 – 300 kg N/ha.  It must be emphasised that data such as these are averages over the season and conceal wide variations in response efficiency within the season.  For example, in perennial ryegrass the spring response is two to three times greater than at other times of the year. Milk production response On intensive dairy pastures, the additional feed produced in response to N fertilization is ideally converted into milk production.  A typical conversion ratio is about 15 kg pasture dry matter per kg milk-solids, or roughly one kg pasture dry matter per liter of milk. In South Africa currently, the value of pasture dry matter in dairy farm operations is estimated to be approximately R2000/ton.  In overseas studies, it has been estimated that the response in terms of milk production ranges from 9 to about 16 kg milk per kg fertilizer N applied.  This arises not because of any significant increase in yield per cow, but from an increase in stocking rate, i.e. cows per hectare. Type of fertilizer Urea and LAN (limestone ammonium nitrate) are the two most important forms of fertilizer N used on pastures, with other products such as ammonium sulphate being used in lesser amounts.  Grasses take up N in both the ammonium and nitrate forms; however, since ammonium (including the N in urea) is converted to nitrate within a few weeks in well-aerated non-acidic soils at temperatures above about 5˚C, most of…

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Feb 08

Eragrostis for Soil Health and Dry Matter Production

By CONSERVATION AGRICULTURE, Nitrogen, Soil Health No Comments

In recent years late spring rains and prevailing drought conditions have put many livestock farmers under severe pressure, especially those who have relied on post-harvest crop residues in combination with natural grassland (veld) to carry their stock. Reductions in maize planting and additional losses in dry matter from veld due to drought conditions have resulted significant deficits in fodder flows. In the light of the above, consideration should be given to the establishment of permanent pastures on marginal lands.  This would serve several purposes, including the conservation of the top soil by ensuring permanent ground cover, and also provide a source of early grazing in spring with the additional potential to harvest several cuts of hay during the summer months to ensure a fodder bank for winter. Eragrostis curvula( E. curvula) also known as “Weeping Love Grass” and “Oulandsgras” was one of four grass species that was selected as a result of the international recognition of the importance of grassland productivity and soil conservation, and is one of the most important pasture grasses in South Africa. E. curvula is easy to establish and generally persists longer than many other species. It has been used with great success for grazing, hay production, a lay pasture after pototo and tobacco production and has played an important role in the prevention of soil erosion by stabilisation of road verges and disturbed soil. There are numerous cultivars available in the market some of which include Ermelo, Agpal, Umgeni, PUK E3, PUK E436 and American Leafy. E. curvula is a tufted subtopical grass with an extensive root system which helps build soil structure. It will survive in areas receiving 400 -1000 mm of rainfall per year and can tolerate soil acid saturations in excess of 70%. It typically grows from September through to March as seen in Graph 1: A well managed pasture may yield four cuts per season if the prevailing conditions are condusive to growth while in drier areas one or two cuts may be achieved. E. curvula yield is a function of rainfall, temperature and nitrogen application and may vary due to geographic location ranging from an excess of 12 tons /ha in the northern areas of the Eastern Cape, Midlands and Northern Kwa Zulu Natal and the cooler areas in eastern Mpumalanga, 6-8 tons/ha in the Free State, 8-10 tons/ha in Gauteng and tapering to 4-6 tons/ha in the western regions of the country. Dry matter yields in excess of 14 tons per ha are attainable with a good fertilization program; even with erratic rainfall, reasonable dry matter and protein yields are attainable, as shown in Graphs 2 – 4 below: Application of N determines dry matter production and improves palatability; additionally, adequate potassium (K) is essential to ensure high yields are maintained. E. curvula is an efficient forager of K, it is important to carry out regular soil tests to ensure that soil K-levels are not ‘mined’ in high production pastures which will result in significant losses in production.  Furthermore, when planning N applications take into…

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Oct 09

Include Ammonium Sulphate in your fertilizer program

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

AFRIKAANS: Maak Ammoniumsulfaat deel van jou bemestingsprogram Specific applications of Ammonium Sulphate may serve as an important source of Nitrogen (21% N) and Sulphur (24%S), for crop production. Ammonium Sulphate can generally be regarded as a suitable supplemental source of nitrogen (N), which can address all Sulphur(S) requirements. Under specific conditions the use of Ammonium Sulphate can result in higher grain yields compared to other N-sources when used as the primary N-source. Before planting Large quantities of Ammonium Sulphate can be broadcast before planting under Centre Pivot Irrigation, especially when soil pH is high and where considerable quantities of plant residues are incorporated in the soil. The volatilization of Ammonium Sulphate is relatively low compared to other N sources, however volatilization can be significant under alkaline conditions and therefore Ammonium Sulphate should rather be incorporated. The application of Ammonium Sulphate as the main source of N before planting could result in higher grain yields compared to other N-sources under specific conditions (Figure 1). Possible reasons for higher yields obtained with Ammonium Sulphate compared to other N-Sources as in Figure 1: Wheat response to S due to S-deficiency in the soil. Less leaching compared to other N-Sources. Under strong alkaline conditions the greater acidifying effect of Ammonium Sulphate can enhance the uptake of other plant nutrients. In Plant Mixtures All N in Ammonium Sulphate is in the ammonium (NH4+) form while most crops prefer a combination of both nitrate (NO3–) and ammonium. Furthermore the conversion of ammonium-N to nitrate-N is usually very slow when band placed. Relatively small amounts of Ammonium Sulphate are incorporated in some granular and liquid plant mixtures to increase the sulphur and ammonium content. Extra ammonium in the plant mixture will accordingly reduce leaching of N in the plant mixture. The application of Ammonium Sulphate as the only source of N in plant mixtures is not recommended. After planting Large quantities of Ammonium Sulphate can be broadcast after planting as the main N-source, either through spreading or Centre Pivot applications. As previously indicated soil incorporation is preferred. The practice of applying up to 100kg Ammonium Sulphate/ha over maize plant rows directly after planting serves as an insurance against possible leaching losses of N in plant mixtures and an effective way of meeting all crop S requirements. The band placement of large quantities of Ammonium Sulphate as the main source of N after planting is not recommended. Mixtures of LAN and Ammonium Sulphate in a ratio of 75% LAN : 25% Ammonium Sulphate (marketed as KANAS by some local fertilizer suppliers)  combines the optimal benefits of both products and contains 26.25% N and 6% S. This ratio of N : S closely resembles the requirement of many crops, with the added benefit that the N is applied in both the ammonium and nitrate forms. Similarly AS is mixed with Ammonium Nitrate Solution to provide a liquid product called Ammonium Sulphate Nitrate (ASN) containing 18% N and 2.4% S. Relatively large quantities of either KANAS or ASN may be…

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Oct 01

Efficacy of LAN compared to urea under dry conditions for maize

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

  AFRIKAANS: Effektiwiteit van KAN teenoor ureum, by verskillende tye van toediening, onder droë omstandighede vir mielies Introduction Nitrogen (N) is normally more efficiently utilized when applied 4 to 8 weeks after planting under high rainfall conditions compared to pre-plant applications (Grove et. al., 1980). In contrast, most N applied 2 weeks after planting showed higher yields than later applications at 5 and 9 weeks after planting under relatively dry conditions (Adriaanse and Human 1993). For applications, 2 weeks after planting a nitrate-N: ammonium-N ratio of 1:1 resulted in higher yield than a 1:0 or 0:1 ratio (Adriaanse and Human, 1993). Similarly it was demonstrated that combinations of nitrate and ammonium were better than either ammonium or nitrate on their own under field conditions (Adriaanse, 1990 and Adriaanse and Human, 1991). When LAN dissolves in soil water it is already in a 1:1 nitrate-N: ammonium-N ratio and readily available for uptake. In contrast urea is not readily available for uptake to the same extent when dissolved in soil water. The rate of direct urea uptake is slower than for either ammonium-N or nitrate-N. Ammonium-N will also inhibit direct urea uptake. Even if nitrate-N concentration is 25% less than urea-N it will still be taken up quicker than urea-N. After hydrolysis, urea will firstly result in a 0:1 nitrate-N: ammonium-N ratio and only after nitrification will more ammonium be converted to nitrate. The time period for these processes to take place may vary from a few days to several weeks. Low temperatures, wet conditions and low soil pH will delay these processes. In addition urea is more toxic, leaches more and is more volatile compared to LAN (Adriaanse 2012a). Many studies have shown better yield responses to LAN compared to urea in long term trials over years as well as over different localities (Adriaanse, 2012a, Adriaanse 2012b, Mangle and Hawkins, 1995, Levington Agriculture, 2009, ITGC, 2004, Avails, 1998). The objectives of this study under a particular dry season were to determine: The optimum timing of N-applications. The efficacy of LAN compared to urea applied 3 weeks before planting, at planting and 3 weeks after planting over different N-rates as knifed in side dressings. To determine the efficacy of LAN compared to urea at different N-rates over time treatments. Materials and Methods Research done by the ARC-GCI in the Viljoenskroon district was carried out over a three year period from 1998 to 2000 on the same plots. The long term annual rainfall average for this area was 592 mm. The soil was from the Avalon form (RSA) or Luvisol (international) containing a soft plinthic layer, varying in depth from 1.2 m to 1.7 m. The soil clay content for different depth increments was 9.1 % from 0 to 15 cm, 10.4 % from 15 to 30 cm and 16.0 % from 30 to 60 cm. Under these specific conditions nitrogen will leach to reach the water in the water table, but it will also move upwards with the water table. Leaching of nitrogen…

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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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Jun 01

SOIL ACIDITY AND ITS MANAGEMENT IN CROP AND PASTURE PRODUCTION

By LIME & LIMING PRODUCTS, PLANT & SOIL NUTRITION, Soil Acidity No Comments

To read article 1/2 click: http://agrispex.co.za/soil-acidity-and-its-management-in-crop-production/ ARTICLE 2/2 THE USE OF LIME AND GYPSUM IN MANAGING SOIL ACIDITY In the first article in this series, we discussed the nature of soil acidity. Particular attention was drawn to the harmful effects of soluble aluminium on root growth and function, and how crop species differ in their ability to tolerate aluminium toxicity. In this second article, we focus on practical aspects of soil acidity management. LIME AND GYPSUM — HOW DO THEY DIFFER? Lime and gypsum are chemically very different products, and consequently their effects on the soil are quite dissimilar. In the agricultural context, ‘lime’ refers to any product in which the calcium and magnesium compounds are able to neutralize soil acidity. Carbonates of calcium and magnesium are the most widely used for this purpose. Dolomitic lime contains a minimum of 15% magnesium carbonate, while calcitic limes have less magnesium carbonate than this. In addition to natural carbonates, various by-products of industrial processes are frequently used as liming materials; these include calcium oxide (burnt lime), calcium hydroxide (slaked lime) and calcium silicate (slag). Gypsum, on the other hand, is calcium sulphate, a neutral salt. It is a valuable calcium and sulphur fertilizer and is much more soluble than lime. In addition, it leaches readily into the subsoil and, in highly weathered (naturally acidic) soils, the sulphate component displaces OH- ions from the clay surfaces. These, in turn, convert soluble aluminium to unavailable aluminium hydroxide. The effectiveness of various liming materials varies widely, with the following factors being particularly important in this regard: Chemical purity ─ the presence or otherwise of non-reactive materials such as sand and clay greatly affects the neutralizing value of the lime (importantly, the colour of the liming material is not a reliable indicator of its quality!). Chemical composition ─ the nature of the calcium and magnesium compounds present. Fineness ─ the finer the lime particles, the faster will be their reaction in the soil. Lime particles larger than 0.84 mm in diameter (about the size of a match head) are of little value. Very coarse liming materials are completely ineffective. Hardness ─ the solubility, and hence neutralizing value, of lime depends on whether it is derived from hard crystalline material or from softer relatively unconsolidated material. Where uncertainty exists as to the quality of a particular liming material, a sample should be submitted for analysis. ACTION OF LIME AND GYPSUM IN SOILS The major effects of lime on soil properties are: an increase in soil pH; a decrease in soluble aluminium and acid saturation levels; an increase in calcium and magnesium levels. The value of dolomitic lime as a magnesium fertilizer is often overlooked. Although several magnesium fertilizers are commercially available, they tend to be prohibitively expensive, and dolomitic lime remains the most cost-effective way of increasing soil magnesium levels. The neutralizing effect of lime on soil aluminium and hydrogen is illustrated in Figure 1. Importantly, the soil must be moist for lime to react. The solid aluminium…

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