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.