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Crop Science

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Browsing Crop Science by Author "Cairns, Andrew Lawrence Patrick."

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    Intercropping of maize and dry beans for the Vulindlela district of KwaZulu-Natal.
    (1997) Liebenberg, Benjamin Christiaan.; Cairns, Andrew Lawrence Patrick.
    The use of a maize/bean intercropping system to improve land productivity was investigated after limited land availability had been identified (Liebenberg, 1993) as a major constraint to crop production in the Vulindlela area of the KwaZulu-Natal province of South Africa. The objective of this study was to develop an intercropping system that would: a) Give an intercrop bean yield approximately equal to that of the sole crop yield, b) Give a maize yield acceptable to the farmer (needed mainly for green maize). c) Produce a land equivalent ratio (LER) greater than one. In order to ensure high bean yields, maize dominance was reduced by lowering the normal maize population of the intercrop by 50% and by using a tramline row arrangement instead of evenly spaced rows. Two bean cultivars namely Mkuzi (carioca) and Umlazi (speckled sugar) and two maize cultivars namely Kalahari Early Pearl (KEP) (an open pollinated cultivar) and SR 52 (a hybrid) were used. Single trials were planted at four localities spread over three seasons i.e. Vulindlela and Ukulinga (1992/93), Cedara (1995/96) and Makhathini (1996). The treatments included varying bean densities, bean planting times and maize harvesting stages. These treatments were compared to maize and bean sole crop controls. High maize yields led to low bean intercrop yields. However, there was little or no difference between sole bean yield and intercrop bean yields associated with lower maize yields. Intercrop maize yields were 50% of the sole maize yields at all the sites. The mean LER's for the Vulindlela and Ukulinga trials were 1.04 and 0.96 respectively while the mean LER's for the Cedara and Makhathini trials were 1.34 and 1.31 respectively. Only the latter two trials displayed significant improvements in land productivity. Mkuzi was more affected by intercropping than Umlazi while KEP competed less with the beans than SR 52 and gave higher yields under less favourable growing conditions. Yield component studies indicated that stress during the vegetative, pod formation, and pod filling stages led to yield reduction in the dry bean crops. Light and leaf nutrient level studies suggested that the yield reduction resulted from competition for nitrogen and light. There was no competition for phosphate and potassium. The study indicates that the intercropping system did meet the desired requirements under conditions that are less than ideal for maize production, such as low soil fertility, water stress and cool temperatures.
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    Nutrient studies in potatoes (Solanum tuberosum)
    (1997) Ahmadi, Ramtin.; Cairns, Andrew Lawrence Patrick.; Greenfield, Peter L.
    One of the biggest problems facing potato (Solanum tuberosum) production in Kwazulu-Natal is acidic soils with high a aluminium content. Traditionally, such soils were ameliorated using lime, thus increasing soil pH, Ca and Mg availability, and reducing Al availability. This study aims to determine the extent to which lime could be replaced by Calmag+B (a Ca source with little ameliorative capacity). The Calmag+B fertiliser increases the soil's Ca content appreciably, but does not alter soil pH and Al availability to the same extent as lime. Pot trials were carried out to determine the effects of liming a highly acid soil, resulting in four levels of amelioration. At each level of amelioration, three levels of Calmag+B were applied to determine whether an optimised yield response would be attained through these applications. Plant emergence and subsequent development was shown to be poor, and in extreme cases absent, under highly acidic soil conditions. Soil amelioration using lime greatly improved plant emergence, development and tuber yield, whereas Calmag+B applications were unable to improve plant emergence, development or tuber yield. The effect of both applications of substantial quantities of Calmag+B to a highly acid soil, and of the dipping of mother tubers in a nutrient solution prior to planting was investigated. The Calmag+B soil applications were unable to improve plant emergence and development. The dipping of the mother tubers in nutrient solution, however, resulted in greatly increased seedling emergence and plant development. This was due to increased nutrient uptake from the mother tuber, and not through increased root development and subsequent nutrient uptake. There were unsubstantiated claims by the manufacturers of Calmag+B that the Mg, NO(3) and B components of the fertiliser would give rise to increased uptake of the Ca component, thus enhancing the efficacy of the fertiliser. Pot trials using a sand medium were employed to test this claim. The trial consisted of interactions of different levels of Ca(2+), Mg(2+), NO(3-), and BO3(2-) applied to the sand medium in the form of a nutrient solution. None of the treatments (barring Ca itself) led to increased Ca uptake by the potato tubers. This would indicate that the claim that the Mg, NO(3) and B components of Calmag+B fertiliser would enhance the uptake of the Ca component are unfounded. It has been suggested that one of the main factors limiting potato production in Kwazulu-Natal has been inadequate mineral nutrition. Certain fertiliser distributors claim that fertiliser application over and above the levels recommended by the Kwazulu-Natal Department of Agriculture Fertiliser Advisory (KDAFA) is the solution to the problem of below potential yield and tuber quality in the province. A field trial was carried out in New Hanover (Kwazulu-Natal), using different levels of Calmag+B and Agrifos, as well as one level of application of KNO(3). All treatments were applied after KDAFA fertiliser recommendations had been fulfilled. At the 95% level of significance, the treatments did not give rise to increased yield and tuber quality. At the 80% level of significance, however, the results indicated that applications of 100kg ha -1 of Calmag+B and KNO(3) would give rise to increased tuber yield.