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…
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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Dr Neil Miles consulting soil scientist
Neil Miles is a consulting soil scientist based in Mount Edgecombe. Prior to entering into consultancy, he spent 28 years with the KZN Department of Agriculture, as a research scientist and research manager, followed by 10 years in research and advisory work with the South African Sugarcane Research Institute (SASRI).
Neil played a leading role in the development of both the Cedara Fertilizer Advisory Service and SASRI’s Fertiliser Advisory Service (FAS). His PhD, through the University of Natal, focused on the nutrition of intensive pastures. Neil’s particular interests are soil health and the nutrition of crops and pastures.
Contact Neil: email@example.com