J. A. J. van Vuuren

Potential Use of Near Infrared Reflectance Monitoring in Precision Agriculture

Abstract The concept of Precision farming is not new, and interest in the potential benefits gained momentum in the late eighties. The high cost of soil sampling and chemical and physical analysis by conventional laboratories has restricted the full implementation of this technique at the field level. Near infrared reflectance (NIR) could be a cost‐effective solution. Soil properties that have been calibrated include gravimetric soil water, clay content, buffer capacity, pH, electrical conductivity, titratable acidity, organic matter, mineralizable nitrogen, potential ammonia volatilization from urea, potential nitrification rate, and urease activity. A whole paradigm shift in philosophy is needed in soil testing to move away from the traditional approach of taking a perceived‐representative sample, in which all the spatial variation is lost, to using a combination of grid soil sampling at a sample intensity of 4 to 10 cores per ha and analysed separately using rapid but less accurate methods such as NIR.

Inter‐laboratory study with regard to the variability of three aglime analysis methods, including a resin suspension method

Abstract An inter‐laboratory study was conducted to determine the variability of three aglime analysis methods. The methods evaluated were; total Ca and Mg analysis, neutralization of 0,5 mol dm‐3 HCl and a resin suspension method. It was found that the resin suspension method not only significantly gave the best reproducibility between laboratories, but it proved to be the most discriminatory between samples, as it is sensitive to all aspects involved, such as fineness, chemical purity and other physical properties.

Alasa: Agricultural laboratory association of southern Africa ‐ ensuring reliable analyses

Abstract Although there have been various quality assurance schemes operative in South Africa for several years, efforts were largely fragmented and informal. Initially the Fertilizer Society of South Africa, together with representatives of Government departments, cooperatives, private laboratories, research councils, and universities met informally to discuss the analysis of materials of agricultural importance: soils, plant material, fertilizers, liming materials, animal feeds, and waters. The need for a more formal structure was long felt and it came to fruition with the formation of Agricultural Laboratory Association of Southern Africa (ALASA) in September 1993. Apart from a constitution, there is a central council comprising representatives of subcommittees representing the different disciplines. Although lots has yet to be put in place, it is confidently expected that this will go a long way to ensuring reliable analyses of materials of agricultural importance in Southern Africa.

Realistic evaluation of liming materials

Soil acidification under tropical and sub-tropical conditions is a well known phenomenon. Because of cost implications in practice it is important that the best available liming materials be used. Various methods have been employed to distinguish between the effectiveness of such materials, most based on the principle of calcium carbonate equivalent. Many of these use relatively strong acids for dissolution of lime, at concentrations far greater than ever actually occur in even the most acid soils. Because contact exchange between the acidified sites and the liming material is considered to be vital, a method in which a slightly acidified cation exchange resin is used was developed (the resin exchange method). This method has been used by several laboratories in South Africa that take part in the quality control scheme run by ALASA. Several problems were experienced in achieving reproducibility between laboratories, that were diagnosed as being due to variations in applications of the method and especially lack of discipline in using a standardized resin. This resulted in a number of independent investigations into reasons for this apparent lack of reproducibility. Reasons for this included inherent particle size distribution in the sub-samples of liming material, resin properties, water quality and electrode maintenance and calibration. Under standardized and controlled conditions the method proved to be eminently satisfactory. An alternative possibility that is being investigated is the use of an unbuffered acid topsoil to replace the resin. A bulk sample could be homogenized and subdivided to provide an adequate supply.Abstract Soil acidification under tropical and sub‐tropical conditions is a well known phenomenon. Because of cost implications in practice it is important that the best available liming materials be used. Various methods have been employed to distinguish between the effectiveness of such materials, most based on the principle of calcium carbonate equivalent. Many of these use relatively strong acids for dissolution of lime, at concentrations far greater than ever actually occur in even the most acid soils. Because contact exchange between the acidified sites and the liming material is considered to be vital, a method in which a slightly acidified cation exchange resin is used was developed (the resin exchange method). This method has been used by several laboratories in South Africa that take part in the quality control scheme run by ALASA. Several problems were experienced in achieving reproducibility between laboratories, that were diagnosed as being due to variations in applications of the method and especially lack of discipline in using a standardized resin. This resulted in a number of independent investigations into reasons for this apparent lack of reproducibility. Reasons for this included inherent particle size distribution in the sub‐samples of liming material, resin properties, water quality and electrode maintenance and calibration. Under standardized and controlled conditions the method proved to be eminently satisfactory. An alternative possibility that is being investigated is the use of an unbuffered acid topsoil to replace the resin. A bulk sample could be homogenized and subdivided to provide an adequate supply.

Soil sampling under fixed cultivation practices.

Abstract Soil sampling by conventional methods as applied in the Republic of South Africa, provides average values. These are valuable for mapping to give an indication of general fertility. The time of sampling generally after the crop has been removed from the field is also not ideal. Values obtained vary markedly from values obtained during planting. In systems where fixed cultivation practices are followed (band placement of fertilisers and row crops) zones of concentration are created in the rootzone that have no resemblance to averages. Acid zones with general lower fertility that are created in this manner are permanent and where crops are subsequently planted in the same position, the intensity of the acidification is enhanced. In time this can cause plant growth in this zone to become impossible. Soil sampling as an aid in fertilisation programme planning requires that the spatial variation must be known. More regular sampling (annually) and possibly throughout the season, on a smaller area, that is representative and part of the system, will give the pattern of variation in the particular field. It must be stressed that acid soils require normal liming if the pH (H2O) is below 6. Acid zones in these soils formed by bandplacement of reduced nitrogen require much higher applications. The mixing of coarse amorphic lime with the fertilisers that are bandplaced can alleviate this. Possible advantages, for example, could be: effectiveness of fertilisers applied on low pH soils, is increased; chemical environment in the root zone is improved; stimulation of beneficial microflora; effectiveness of band applied herbicides may be improved; a strong tendency towards higher yields. No harmful effects were encountered in a study of these aspects. Unavailability of P due to the formation of less soluble Ca‐phosphate as well as Zn‐interactions are some of the theoretical possibilities, although none of these were encountered. Addition of coarse lime to fertilisers that are bandplaced, is a safe and affordable procedure.Soil sampling by conventional methods as applied in the Republic of South Africa, provides average values. These are valuable for mapping to give an indication of general fertility. The time of sampling generally after the crop has been removed from the field is also not ideal. Values obtained vary markedly from values obtained during planting. In systems where fixed cultivation practices are followed (band placement of fertilisers and row crops) zones of concentration are created in the rootzone that have no resemblance to averages. Acid zones with general lower fertility that are created in this manner are permanent and where crops are subsequently planted in the same position, the intensity of the acidification is enhanced. In time this can cause plant growth in this zone to become impossible. Soil sampling as an aid in fertilisation programme planning requires that the spatial variation must be known. More regular sampling (annually) and possibly throughout the season, on a smaller area, that is representative and part of the system, will give the pattern of variation in the particular field. It must be stressed that acid soils require normal liming if the pH (H 2 O) is below 6. Acid zones in these soils formed by bandplacement of reduced nitrogen require much higher applications. The mixing of coarse amorphic lime with the fertilisers that are bandplaced can alleviate this. Possible advantages, for example, could be: effectiveness of fertilisers applied on low pH soils, is increased; chemical environment in the root zone is improved; stimulation of beneficial microflora; effectiveness of band applied herbicides may be improved; a strong tendency towards higher yields. No harmful effects were encountered in a study of these aspects. Unavailability of P due to the formation of less soluble Ca-phosphate as well as Zn-interactions are some of the theoretical possibilities, although none of these were encountered. Addition of coarse lime to fertilisers that are bandplaced, is a safe and affordable procedure.

Functioning of Alasa (Agri Laboratory Association of Southern Africa).

Abstract ALASA is a non‐profitable umbrella body for laboratories with agricultural relevance and was founded in 1993. Its mission is to promote the interests of member laboratories and to gain recognition for their services and to ensure the acceptable quality thereof. The main aims of ALASA are to establish and maintain standard analytical methods, promote the use of the standardized methods, rationalize methods, support and institute analytical quality assurance schemes and inter‐calibration exercises and the promotion of accreditation of member laboratories. The main functions of ALASA are to liaison with interested parties, member laboratories and other organizations, to promote standardization and quality assurance, organization of suitable workshops, congresses and courses. ALASA is governed by its council consisting of a President, chairperson of the executive committee, secretary and treasurer. The elected chairperson and secretary of each sub‐committee plus two additional members serve on the council. Currently the following sub disciplines are active: plants, soil and growth media, lime, fertilizer, feed, pesticide, water and wine. Sub‐committees meet regularly to discuss and co‐ordinate matters that concern the specific discipline and report back to the council. Problems which ALASA has encountered and which cause variation in analytical results are the incorrect application of methods, the use of different instrumentation and the use of non‐standardized methods. Some of the main achievements of ALASA includes the compilation of standard analytical handbooks for soil (presently under revision), fertilizers and a combined book for plant and feed. Other achievements include the presentation of workshops where the correct methodologies for different methods, which cause reduced variation in the analytical results in the different control schemes, are discussed and explained.ALASA is a non-profitable umbrella body for laboratories with agricultural relevance and was founded in 1993. Its mission is to promote the interests of member laboratories and to gain recognition for their services and to ensure the acceptable quality thereof. The main aims of ALASA are to establish and maintain standard analytical methods, promote the use of the standardized methods, rationalize methods, support and institute analytical quality assurance schemes and inter-calibration exercises and the promotion of accreditation of member laboratories. The main functions of ALASA are to liaison with interested parties, member laboratories and other organizations, to promote standardization and quality assurance, organization of suitable workshops, congresses and courses. ALASA is governed by its council consisting of a President, chairperson of the executive committee, secretary and treasurer. The elected chairperson and secretary of each sub-committee plus two additional members serve on the council. Currently the following sub disciplines are active: plants, soil and growth media, lime, fertilizer, feed, pesticide, water and wine. Sub-committees meet regularly to discuss and co-ordinate matters that concern the specific discipline and report back to the council. Problems which ALASA has encountered and which cause variation in analytical results are the incorrect application of methods, the use of different instrumentation and the use of non-standardized methods. Some of the main achievements of ALASA includes the compilation of standard analytical handbooks for soil (presently under revision), fertilizers and a combined book for plant and feed. Other achievements include the presentation of workshops where the correct methodologies for different methods, which cause reduced variation in the analytical results in the different control schemes, are discussed and explained.

Data presentation, interpretation, and communication

Abstract Soil sampling by conventional methods as applied in the Republic of South Africa, provides average values. These are valuable for mapping to give an indication of general fertility. The time of sampling generally after the crop has been removed from the field is also not ideal. Values obtained vary markedly from values obtained during planting. In systems where fixed cultivation practices are followed (band placement of fertilisers and row crops) zones of concentration are created in the rootzone that have no resemblance to averages. Acid zones with general lower fertility that are created in this manner are permanent and where crops are subsequently planted in the same position, the intensity of the acidification is enhanced. In time this can cause plant growth in this zone to become impossible. Soil sampling as an aid in fertilisation programme planning requires that the spatial variation must be known. More regular sampling (annually) and possibly throughout the season, on a smaller area, that is representative and part of the system, will give the pattern of variation in the particular field. It must be stressed that acid soils require normal liming if the pH (H2O) is below 6. Acid zones in these soils formed by bandplacement of reduced nitrogen require much higher applications. The mixing of coarse amorphic lime with the fertilisers that are bandplaced can alleviate this. Possible advantages, for example, could be: effectiveness of fertilisers applied on low pH soils, is increased; chemical environment in the root zone is improved; stimulation of beneficial microflora; effectiveness of band applied herbicides may be improved; a strong tendency towards higher yields. No harmful effects were encountered in a study of these aspects. Unavailability of P due to the formation of less soluble Ca‐phosphate as well as Zn‐interactions are some of the theoretical possibilities, although none of these were encountered. Addition of coarse lime to fertilisers that are bandplaced, is a safe and affordable procedure.Soil sampling by conventional methods as applied in the Republic of South Africa, provides average values. These are valuable for mapping to give an indication of general fertility. The time of sampling generally after the crop has been removed from the field is also not ideal. Values obtained vary markedly from values obtained during planting. In systems where fixed cultivation practices are followed (band placement of fertilisers and row crops) zones of concentration are created in the rootzone that have no resemblance to averages. Acid zones with general lower fertility that are created in this manner are permanent and where crops are subsequently planted in the same position, the intensity of the acidification is enhanced. In time this can cause plant growth in this zone to become impossible. Soil sampling as an aid in fertilisation programme planning requires that the spatial variation must be known. More regular sampling (annually) and possibly throughout the season, on a smaller area, that is representative and part of the system, will give the pattern of variation in the particular field. It must be stressed that acid soils require normal liming if the pH (H 2 O) is below 6. Acid zones in these soils formed by bandplacement of reduced nitrogen require much higher applications. The mixing of coarse amorphic lime with the fertilisers that are bandplaced can alleviate this. Possible advantages, for example, could be: effectiveness of fertilisers applied on low pH soils, is increased; chemical environment in the root zone is improved; stimulation of beneficial microflora; effectiveness of band applied herbicides may be improved; a strong tendency towards higher yields. No harmful effects were encountered in a study of these aspects. Unavailability of P due to the formation of less soluble Ca-phosphate as well as Zn-interactions are some of the theoretical possibilities, although none of these were encountered. Addition of coarse lime to fertilisers that are bandplaced, is a safe and affordable procedure.

Analytical methods and quality assurance

A gn LASA (Agri Laboratory Association of Southern Africa) has 75 member laboratories participating in quality audits that service different sectors in Agriculture, Horticulture and Environmental needs. Most laboratories are fairly small and only render a limited service. In 1968 Government and the private sector agreed to rationalise and centralise laboratory services in SA. As frequently happens the ideal did not prevail and soon afterwards everyone reverted to doing their own thing. In 1996 the major role players in the private sector re-evaluated their positions and as the trend to convert from Co-operatives to Companies gathered momentum, pressure on laboratories to become self-reliant increased. A complicating factor had always been that Government, to a large extent, subsidised analytical services in Agriculture. The first major amalgamation occurred with the combining of the laboratories of Northwest Co-operative, Outspan International (Previous Citrus Exchange) and the in-house feed laboratories of Meadow Feeds (Northern Region) to form a new company, Central Agricultural Laboratories situated at Pelindaba. CAL is the largest agricultural laboratory in Southern Africa rendering an extensive analytical and advisory service. The major private companies as well as Co-operatives make use of CALs services. CAL is also contracted by Government to do all regulatory samples for Fertiliser, Lime, Growth Media and Animal Feeds. Advisory services related to soil, leaf, fruit, water and fertiliser analyses are available to clients. The establishments of satellite laboratories in other parts of Southern Africa are presently being investigated. Economy of scale obviously prevails and CAL, due to the large number of samples handled, has been economically viable within the first year of operation. The first major overseas contract, from a British company involved in Africa, has been completed.Abstract AgriLASA (Agri Laboratory Association of Southern Africa) has 75 member laboratories participating in quality audits that service different sectors in Agriculture, Horticulture and Environmental needs. Most laboratories are fairly small and only render a limited service. In 1968 Government and the private sector agreed to rationalise and centralise laboratory services in SA. As frequently happens the ideal did not prevail and soon afterwards everyone reverted to doing their own thing. In 1996 the major role players in the private sector re‐evaluated their positions and as the trend to convert from Co‐operatives to Companies gathered momentum, pressure on laboratories to become self‐reliant increased. A complicating factor had always been that Government, to a large extent, subsidised analytical services in Agriculture. The first major amalgamation occurred with the combining of the laboratories of Northwest Co‐operative, Outspan International (Previous Citrus Exchange) and the in‐house feed laboratories of Meadow Feeds (Northern Region) to form a new company, Central Agricultural Laboratories situated at Pelindaba. CAL is the largest agricultural laboratory in Southern Africa rendering an extensive analytical and advisory service. The major private companies as well as Co‐operatives make use of CALs services. CAL is also contracted by Government to do all regulatory samples for Fertiliser, Lime, Growth Media and Animal Feeds. Advisory services related to soil, leaf, fruit, water and fertiliser analyses are available to clients. The establishments of satellite laboratories in other parts of Southern Africa are presently being investigated. Economy of scale obviously prevails and CAL, due to the large number of samples handled, has been economically viable within the first year of operation. The first major overseas contract, from a British company involved in Africa, has been completed.

Developments in agricultural analytical services in Southern Africa.

A gn LASA (Agri Laboratory Association of Southern Africa) has 75 member laboratories participating in quality audits that service different sectors in Agriculture, Horticulture and Environmental needs. Most laboratories are fairly small and only render a limited service. In 1968 Government and the private sector agreed to rationalise and centralise laboratory services in SA. As frequently happens the ideal did not prevail and soon afterwards everyone reverted to doing their own thing. In 1996 the major role players in the private sector re-evaluated their positions and as the trend to convert from Co-operatives to Companies gathered momentum, pressure on laboratories to become self-reliant increased. A complicating factor had always been that Government, to a large extent, subsidised analytical services in Agriculture. The first major amalgamation occurred with the combining of the laboratories of Northwest Co-operative, Outspan International (Previous Citrus Exchange) and the in-house feed laboratories of Meadow Feeds (Northern Region) to form a new company, Central Agricultural Laboratories situated at Pelindaba. CAL is the largest agricultural laboratory in Southern Africa rendering an extensive analytical and advisory service. The major private companies as well as Co-operatives make use of CALs services. CAL is also contracted by Government to do all regulatory samples for Fertiliser, Lime, Growth Media and Animal Feeds. Advisory services related to soil, leaf, fruit, water and fertiliser analyses are available to clients. The establishments of satellite laboratories in other parts of Southern Africa are presently being investigated. Economy of scale obviously prevails and CAL, due to the large number of samples handled, has been economically viable within the first year of operation. The first major overseas contract, from a British company involved in Africa, has been completed.Abstract AgriLASA (Agri Laboratory Association of Southern Africa) has 75 member laboratories participating in quality audits that service different sectors in Agriculture, Horticulture and Environmental needs. Most laboratories are fairly small and only render a limited service. In 1968 Government and the private sector agreed to rationalise and centralise laboratory services in SA. As frequently happens the ideal did not prevail and soon afterwards everyone reverted to doing their own thing. In 1996 the major role players in the private sector re‐evaluated their positions and as the trend to convert from Co‐operatives to Companies gathered momentum, pressure on laboratories to become self‐reliant increased. A complicating factor had always been that Government, to a large extent, subsidised analytical services in Agriculture. The first major amalgamation occurred with the combining of the laboratories of Northwest Co‐operative, Outspan International (Previous Citrus Exchange) and the in‐house feed laboratories of Meadow Feeds (Northern Region) to form a new company, Central Agricultural Laboratories situated at Pelindaba. CAL is the largest agricultural laboratory in Southern Africa rendering an extensive analytical and advisory service. The major private companies as well as Co‐operatives make use of CALs services. CAL is also contracted by Government to do all regulatory samples for Fertiliser, Lime, Growth Media and Animal Feeds. Advisory services related to soil, leaf, fruit, water and fertiliser analyses are available to clients. The establishments of satellite laboratories in other parts of Southern Africa are presently being investigated. Economy of scale obviously prevails and CAL, due to the large number of samples handled, has been economically viable within the first year of operation. The first major overseas contract, from a British company involved in Africa, has been completed.

Analytical methods and quality assurance: Developments in agricultural analytical services in Southern Africa

A gn LASA (Agri Laboratory Association of Southern Africa) has 75 member laboratories participating in quality audits that service different sectors in Agriculture, Horticulture and Environmental needs. Most laboratories are fairly small and only render a limited service. In 1968 Government and the private sector agreed to rationalise and centralise laboratory services in SA. As frequently happens the ideal did not prevail and soon afterwards everyone reverted to doing their own thing. In 1996 the major role players in the private sector re-evaluated their positions and as the trend to convert from Co-operatives to Companies gathered momentum, pressure on laboratories to become self-reliant increased. A complicating factor had always been that Government, to a large extent, subsidised analytical services in Agriculture. The first major amalgamation occurred with the combining of the laboratories of Northwest Co-operative, Outspan International (Previous Citrus Exchange) and the in-house feed laboratories of Meadow Feeds (Northern Region) to form a new company, Central Agricultural Laboratories situated at Pelindaba. CAL is the largest agricultural laboratory in Southern Africa rendering an extensive analytical and advisory service. The major private companies as well as Co-operatives make use of CALs services. CAL is also contracted by Government to do all regulatory samples for Fertiliser, Lime, Growth Media and Animal Feeds. Advisory services related to soil, leaf, fruit, water and fertiliser analyses are available to clients. The establishments of satellite laboratories in other parts of Southern Africa are presently being investigated. Economy of scale obviously prevails and CAL, due to the large number of samples handled, has been economically viable within the first year of operation. The first major overseas contract, from a British company involved in Africa, has been completed.Abstract AgriLASA (Agri Laboratory Association of Southern Africa) has 75 member laboratories participating in quality audits that service different sectors in Agriculture, Horticulture and Environmental needs. Most laboratories are fairly small and only render a limited service. In 1968 Government and the private sector agreed to rationalise and centralise laboratory services in SA. As frequently happens the ideal did not prevail and soon afterwards everyone reverted to doing their own thing. In 1996 the major role players in the private sector re‐evaluated their positions and as the trend to convert from Co‐operatives to Companies gathered momentum, pressure on laboratories to become self‐reliant increased. A complicating factor had always been that Government, to a large extent, subsidised analytical services in Agriculture. The first major amalgamation occurred with the combining of the laboratories of Northwest Co‐operative, Outspan International (Previous Citrus Exchange) and the in‐house feed laboratories of Meadow Feeds (Northern Region) to form a new company, Central Agricultural Laboratories situated at Pelindaba. CAL is the largest agricultural laboratory in Southern Africa rendering an extensive analytical and advisory service. The major private companies as well as Co‐operatives make use of CALs services. CAL is also contracted by Government to do all regulatory samples for Fertiliser, Lime, Growth Media and Animal Feeds. Advisory services related to soil, leaf, fruit, water and fertiliser analyses are available to clients. The establishments of satellite laboratories in other parts of Southern Africa are presently being investigated. Economy of scale obviously prevails and CAL, due to the large number of samples handled, has been economically viable within the first year of operation. The first major overseas contract, from a British company involved in Africa, has been completed.