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…
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…
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…
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…
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…
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.
ARTICLE 1/2 THE NATURE OF SOIL ACIDITY AND IT’S DIAGNOSIS Acid soil conditions restricting crop growth occur widely in the eastern parts of South Africa. In the higher rainfall areas, soils are often naturally acidic; however, human intervention may accelerate acidification. It is worth noting that soil acidity problems are by no means unique to this country: worldwide, approximately 30% of the land available for cultivation is acidic. Farmers frequently have difficulty in getting to grips with the various soil acidity parameters listed in soil test reports, and furthermore, may be presented with conflicting advice regarding the use of products such as lime and gypsum. The purpose of these articles is to provide scientifically sound and practically useful answers to questions such as: “What exactly is soil acidity?”, “How does it impact crops?”, and “How is it best managed?” SOIL ACIDITY – WHAT IS IT, AND WHAT CAUSES IT? In order to gain a working understanding of soil acidity, there is a need to touch on some basic soil chemistry. Clays and organic matter in the soil carry a negative charge. In a soil that is not acidic, this negative charge is balanced by the positive charge on certain plant nutrients, in particular, calcium (Ca++) magnesium (Mg++) and potassium (K+). As soils acidify, concentrations of other non-nutrient elements, in particular hydrogen (H+) and aluminium (Al+++), as well as manganese (Mn++), increase, and they take the place of nutrients such as calcium and magnesium on the clays and organic matter (Figure 1). Under non-acidic conditions, the aluminium and manganese are contained in the clay and other soil mineral particles, but as acidity increases, clay edges start dissolving, releasing soluble aluminium and manganese into the soil. Importantly, from the perspective of managing soil acidity, it is the soluble aluminium, and sometimes manganese, which are the most important growth-limiting factors in acid soils. Furthermore, it must be borne in mind that pH measures only the concentration of hydrogen in the soil, and not that of aluminium and manganese. These considerations are of cardinal importance in terms of the development of economically sound recommendations for the correction of acidity problems. What causes soils to acidify? Although, as noted earlier, acid soils occur widely in nature, the following human activities may markedly accelerate acidification: Acid rain, resulting from atmospheric pollution by industry. This has been shown to be a major contributory factor in some Highveld areas. The use of nitrogenous fertilizers, particularly when applied in excess of immediate crop requirements. The removal of basic nutrients (calcium, magnesium and potassium) in harvested crops and animal products. Accelerated decomposition of soil organic matter as a result of tillage. SOIL ACIDITY – EFFECTS ON CROP GROWTH The effects of soil acidity on crop growth tend to be insidious, in that it is in the root zone where the major impact occurs. Damage caused to the root system and the unfavourable soil chemistry associated with excessive acidity are translated into poor crop growth, with there frequently being no classical…
Ruth Rhodes previously worked for The South African Sugar Research Institute (SASRI) as a soil scientist and is now a private consultant, delivered a well balanced and objective presentation on the definition of soil health, highlighting some prevalent factors affecting soil health and methods of quantifying soil health. Rhodes initiated the concept of soil health by highlighting “how every soil tells a story” as illustrated below where two soils that started out identically thirty years ago ended up so different due to land use and management: The “term soil health” today is used interchangeably with the terms “soil quality” and “soil condition” and there are various definitions that are used to describe soil health: A state of a soil meeting its range of ecosystem functions as appropriate to its environment. Soil health / quality describes soils that are not only fertile but also posses adequate physical and biological properties to “sustain productivity, maintain environment quality and promote plant and animal health”- Doron 1994. “how well soil does what we want it to do” – USDA Rhodes pointed out that there are many other definitions however we should want our soils to support and grow optimally yielding crops, “forever” without harming the environment. The soil food web may be used as the starting point in assessing soil health, however there are over forty different factors that determine soil health which can be grouped into biological factors, physical factors, chemical factors and nutritional factors. Rhodes aptly likened these groups of factors to being the pieces of a puzzle and that if on piece was missing then the puzzle is incomplete: Soil health shouldn’t be viewed in terms of biology only as it is comprised by a whole range of different factors, of the these there are only two inherent qualities that we can’t really control and aren’t affected by management easily; soil depth and texture. They are determined by the factors of soil formation such as climate, topography, vegetation, parent material and time which give soils some kind of inherent health or quality for example comparing a loamy soil to a sandy soil. A loamy soil may seen to be more healthy because it has a higher water holding capacity; or referred to as having a higher “soil capability’. Dynamic qualities affect soil quality or condition that we can manage, Rhodes proceeded to briefly highlight some of these factors and how the changing nature of soil properties determining soil health may be affected by management. Chemical and Nutritional factors Soil Acidity is a significant yield limiting factor in dryland agriculture in South Africa especially in KZN and the Eastern Cape and is starting to become a problem in irrigation areas which until recently have not been a familiar with this problem. Soil acidity initially starts off in small patches that expand if not rectified, they can often be identified as areas displaying poor growth (in severe cases not even weeds will grow); “seed vigour” and germination problems resulting from soil acidity have…
Stephanie Roberts, Agronomic R&D Manager for Omnia gave a very informative presentation on the significance and market potential of biostimulants, biofertilizers and biopesticides including a detailed explanation of the definitions, differences and challenges surrounding the use of these products; especially in relation to Group 3 fertilizer registration in South Africa. There is tremendous interest in this market commercially as worldwide growth of the global stimulants market is expected to reach US$ 3.2 billion within the next five years while the humanitarian challenge increases as agriculture will be expected to feed an extra 400 million mouths in the next five years. Bioproducts can help to sustainably improve crop yields by reducing crop stress and improving nutrient use efficiency. However this segment of the industry faces challenges of perception as many of these products have been described with dubious claims and a mysterious technical story leading to them being labelled as “muck and magic” in the United Kingdom and “snake oils” in the USA. Some reasons that these perceptions have arisen: Many products such as kelps and amino acids derived from fish emulsions originated from the organic farming industry which has been associated with not always using the best science available. Many of these products were developed from industry driven R&D and not from Universities, even in Universities there is mistrust relating to these products. Problems of fake products; for example where people are selling caramel colourants and labelling them as “humic”. Unfortunately the genuine products don’t always work and cannot be guaranteed to always give a proper response. A lesson from the “American Snake Oil” industry The original snake oils were used by Chinese immigrants who built the transcontinental railroad in the USA in the 1880’s to ease muscle pain. The Americans realized the potential and used extracts from rattlesnakes when the original snake oil ran out as an alternative, soon unscrupulous businessmen were selling mineral oil as snake oil; which led to snake oil gaining the reputation as something not to be trusted. A hundred years later it was found that Chinese water snakes did indeed carry Omega 3 fatty acids which have anti-inflammatory properties. The lesson from the snake oil industry is that the problem was not related to product but rather to the fake product. As Roberts explained that the purpose of Group 3 registration is to ensure that biostimulants and biofertilizers aren’t registered as Remedies but as fertilizers and that biopesticides remain registered as Remedies. It is most important to ensure that only proven biostimulants and biofertilizers are marketed to farmers and for the industry to validate the products being sold so that the market is not destroyed by non-regulated non proven products. The definition of Biostimulants according to the current Group 3 regulations of Act 36: “A fertilizer containing natural or synthetic substance(s) or organism(s) or maintain(s) the growth or yield of plants or the physical, chemical or biological condition (fertility) of the soil; and “soil improver” shall have the same meaning“. The major challenge facing…
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