Efficacy of LAN compared to urea under dry conditions for maize

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  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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Welcome to Agrispex; I’m delighted to officially launch Agrispex today as I begin my 30th year of service to the fertilizer industry. There is no doubt that climate change is a reality as is the fact that the world population will increase by 400 million people within the next five years, placing greater demands on agriculture to produce staple foods while at the same competing with urban populations and industry for limited water resources and arable land. Exciting advances in agricultural production including the integrated use of bio-fertilizers, bio-stimulants and bio-pesticides in fertilizer programs combined with new technologies continue to  enable commercial agriculture to successfully face the challenges of increasing  production costs and fluctuating returns determined by the supply and demand for safe food. South African soil erosion losses are estimated to be 300 million tons per year which combined with the losses of soil nutrients, soil organic matter, reduced soil water holding capacity  and increased soil acidification collectively threaten sustainability. The adoption of conservation agriculture practices are essential for long term maintenance of our soils, biodiversity and natural systems; especially our rivers, estuaries and marine ecosystems. The long term aim of Agrispex is to promote  soil productivity and the conservation of agri-ecosystems through the publication of scientifically based short articles that are easy to read, can be understood by the layman and serve as an on-line technical manual for students, farmers, agricultural advisors and marketers in the future. I trust that you find the current and future articles published useful and interesting and wish you successful visits to Agrispex in the future.  

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