Radiation interception and use in a maize and bean intercropping system
English: Food shortage is known to have been caused by overpopulation, natural disasters and poor food distribution. In areas facing food insecurity, such as Africa, peasants or smalIscale farmers have practised traditional cropping techniques since old times. One of the techniques is intercropping, and many intereropping studies have been reported since the 1960s. According to those studies, intereropping has higher productivity and also higher resource use than sole cropping, however, the contribution of crop radiation utilisation to that higher productivity is unclear. From this background, a quest as to whether intereropping was suitable to small-scale farming in a semi-arid region (Free State, South Africa) has started. The main aim of this study was to analyse and model radiation interception and employment in a maize-bean intereropping system with alternate (northsouth and east-west) row directions (Chapters 3 and 4). Also, the intererop yield advantage was assessed in terms of intensity of land use, accumulation of energy and return of cash increment (Chapter 2); and photosynthetically active radiation (PAR) above plant canopies was investigated (Chapter 5). In Chapter 2 it was shown that the maize-bean intereropping had a yield advantage, compared with the sole cropping, under the set conditions used for both maize and beans planting. In other words, maize-bean intereropping was equivalent in yield to sole maize, and gave a higher yield than sole beans. This was explained by crop radiation interception and use in Chapter 3. The intereropping was analogous to maize sole cropping in the overall efficiency of radiation interception and use, and had greater radiation interception and use than bean sole cropping. In addition, no difference in crop productivity and efficiency was found between row direction treatments. In the modelling study (Chapter 4), the intercropped maize had the same growth efficiency as the sole cropped maize, but beans had greater radiation utilisation in intereropping than in sole cropping. This resulted in an intereropping yield advantage. In Chapter 5, an empirical equation for estimating PAR from solar radiation has been introduced because PAR is not routinely measured at weather stations. The equation may be accurate enough to compute PAR from the large data sets available across southern Africa. This study has shown that planting maize in association with beans is advantageous compared with separate planting, in both crop productivity and efficiency. Normally, small-scale farmers cultivate not one crop but a staple crop and supplement crops. From this point of view, the conclusion is drawn that intereropping is suitable for use in the small-scale farming sector.
Afrikaans: Dit is bekend dat oorbevolking, natuurrampe en gebrekkige voedselverspreiding grotendeels die oorsaak van voedseltekorte is. In gebiede soos Afrika, waar voedselonsekerheid die arm bevolking of kleinskaalboere dikwels in die gesig staar, is boere goed vertroud met die tradisionele verbouingstegnieke van toeka se dae. Een van die tegnieke is tussen- of kruisverbouing wat die studieveld al in die 1960s betree het. Volgens bewese resultate lewer tussenverbouing hoër opbrengste en veral hoër gewashulpbronverbruik as enkelverbouing. Na aanleiding van hierdie agtergrond is daar gepoog om die gepastheid van kruisverbouing op kleinskaalboerdery in die semi-ariede area (Bloemfontein, Vrystaat, Suid Afrika) na te vors en is 'n studie uitgevoer om gewasstralingsonderskepping en verbruik van gewasstraling te ondersoek. Die hoofdoel van die studie is die analise en modellering van stralingsonderskepping en verbruik in die mielie/bone tussenverbouing met twee verskillende (noord-suid en oos-wes) ryrigtings (Hoofstukke 3 en 4). Verder is die kruisverbouingsopbrengsvoordeel bereken in terme van intensitiet van landsverbruik, akkumerlering van energie en geldverdienste (Hoofstuk 2) en is ondersoek ingestel na fotosintetiese aktiewe sraling (FAS), wat die primêre faktor' is in plantegroei bokant plantgewasdakke (Hoofstuk 5). In Hoofstuk 2 is bewys dat tussenverbouing 'n opbrengsvoordeel teenoor monoverbouing toon, met die veronderstelling dat beide mielies en bone geplant word. Met ander woorde, mielie-bone tussenverbouing is ekwivalent in opbrengs aan slegs mielies en toon 'n hoër opbrengs as slegs bone. Hierdie verskynsel word deur gewasstralingsonderskepping en - verbruik in Hoofstuk 3 behandel. Die tussenverbouing het ooreengekom met slegs mielieverbouing in die algehele doeltreffendheid van stralingsonderskepping en verbruik en wys hoër stralingsonderskepping en verbruik as die geval by slegs boneverbouing. Verder, geen verskil is tussen ryrigting behandelings op opbrengste en doeltreffendheid gevind nie. In Hoofstuk 4 (modelleringstudie) is gevind dat die tussenverboude mielies dieselfde groeidoeltreffendheid as slegs verboude mielies het, maar dat bone groter stralingsverbruik by tussenverbouing as by monoverbouing toon. Dit kan lei tot die tussenverboude opbrengsvoordeel. In Hoofstuk 5 word 'n empiriese vergelyking vir berekening van FAS vanaf straling voorgestel, omdat FAS nie normaalweg gemeet word deur weerstasies nie. Die vergelyking mag akkuraat genoeg wees om FAS by groot datastelle te bereken. Hierdie studie het bewys dat die gesamentlike aanplanting van mielies en bone voordelig is vir gewasproduktiwiteit en doeltreffendheid, in vergelyking met afsonderlike aanplanting. Gewoonlik sal kleinboere nie 'n enkele gewas nie, maar 'n hoofvoedselgewas plus supplementêre gewasse kweek. Die gevolgtrekking is dus gemaak dat tussenverbouing gepas is vir kleinskaalboerdery.