Utilisation of cover crops : implications for conservation agriculture systems

Smit, Ernst Hendrik (2019-04)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Cover crops have the potential to address some limitations in conservation agriculture systems with a Mediterranean climate. These limitations include, but are not limited to, a lack in crop diversity, herbicide resistant weeds, insufficient soil cover, and degraded soil. Mediterranean climates restrict cover crop production to the winter growing season when crops are normally planted. This increase the financial cost of cover crops as the implementation of cover crops replace one season’s production. In order to salvage some of the costs of cover crop production, the cover crops can be utilised. It is, however, not clear how utilisation of cover crops will influence the functional role of cover crops. This study aims to investigate how cover crops and the utilisation of cover crops affect the productivity of a system. A trial was conducted in 2016 in the Swartland region of South Africa, characterised by a Mediterranean-type climate. In the first year of the trial, two cover crop mixtures (a mixture containing mainly cereal crops and another containing mainly leguminous crops) were planted. Each of the mixtures were utilised in three ways: i) mowed and removed as hay, ii) grazed by sheep and iii) rolled and left unutilised. In the succeeding year (2017), wheat was planted on all the plots and a control was included (wheat on plots where wheat was cultivated for the previous two years). Cover crop utilisation reduced (p < 0.05) the quantity of soil cover, but not necessarily (p > 0.05) the amount of minerals in the soil cover. In addition to this, grazing of cover crops improved (p < 0.05) soil N. In a dry year cover crop cultivation did not increase (p < 0.05) the succeeding wheat grain production, irrespective of cover crop utilisation in the previous year. A mainly leguminous cover crop mixture, however, can increase (p < 0.05) the wheat grain protein content. The results indicate that utilisation of cover crops improve nutrient cycling. Cover crops do not always improve succeeding cash crop yield, which in turn could increase the risk on investment for producers. The implementation of cover crops improved (p < 0.05) cash crop quality, but not (p < 0.05) the grain yield of the cash crop. This indicates that the positive effect of cover crops on succeeding cash crops will not always compensate for the financial cost involved in cultivating cover crops. The only negative effect of grazing the mainly leguminous mixture was a reduction (p < 0.05) in the quantity soil cover, but the same treatment increased (p < 0.05) soil N. Despite the reduction in soil cover following utilisation, soil was still sufficiently covered according to conservation agriculture norms. This indicates that the utilisation of cover crops can generate an additional income and improve the economic viability of cover crop production.

AFRIKAANSE OPSOMMING: Dekgewasse het die potensiaal om sekere beperkings in bewaringslandboustelsels binne ’n meditereënse klimaat aan te spreek. Hierdie beperkings sluit in, maar is nie beperk tot ’n gebrek aan gewasdiversiteit, onkruiddoderweerstandigheid van onkruide, onvoldoende grondbedekking en degradeerde grond nie. Mediterreënse klimaat beperk dekgewasproduksie tot die winterseisoen wanneer kontantgewasse gewoonlik geplant word. Dit verhoog die finansiële koste van dekgewasse, aangesien die implementering van dekgewasse die een seisoen se produksie vervang. ’n Gedeelte van die koste verbonde aan dekgewasproduksie kan deur die benuting van dekgewasse verhaal word. Dit is egter nie duidelik hoe die benutting van dekgewasse die funksionele rol van dekgewasse sal beïnvloed nie. Die doel van hierdie studie is om te ondersoek hoe dekgewasse en die benutting van dekgewasse produktiwiteit van 'n stelsel sal beïnvloed. In die Swartland (met ’n mediterreense klimaat), Suid-Afrika is ’n proef in 2016 uitgevoer. In die eerste jaar van die proef is twee dekgewasmengsels (’n mengsel wat hoofsaaklik graangewasse bevat en 'n ander wat hoofsaaklik peulgewasse bevat) geplant. Elk van die mengsels is op drie maniere benut: i) gesny en verwyder as hooi, ii) bewei deur skape en iii) gerol en onbenut gelaat. In die daaropvolgende jaar (2017) is koring op al die persele geplant en 'n kontrole is ingesluit (koring op persele waar koring vir die voorafgaande twee jaar verbou was). Dekgewasbenutting verminder (p < 0.05) die hoeveelheid grondbedekking, maar nie noodwendig (p > 0.05) die hoeveelheid minerale in die grondbedekking nie. Daarbenewens het weiding van dekgewasse grond N verbeter (p < 0.05). In 'n droë jaar het die verbouing van dekgewasse nie die opvolgende koring-graanproduksie verhoog nie (p < 0.05), ongeag die benutting van degewasse in die voorafgande jaar. 'n Hoofsaaklik peuldekgewas mengsel kan egter (p < 0.05) die koring-graanproteïeninhoud verhoog. Hierdie resultate dui daarop dat die gebruik van dekgewasse die voedingstofsiklus verbeter. Dekgewasse verbeter nie altyd die produksie van opvolgende kontantgewasse nie, wat die risiko op belegging vir produsente kan verhoog. Die implementering van dekgewasse het kontantgewasgehalte verbeter (p < 0.05), maar nie die graanopbrengs (p < 0.05) van die kontantgewas nie. Dit dui daarop dat die positiewe effek van dekgewasse op die daaropvolgende kontantgewasse nie altyd sal kan kompenseer vir die finansiële koste verbonde aan dekgewasse verbouing nie. Die enigste negatiewe effek van die weiding van die hoofsaaklik peuldekgewas-mengsel was 'n vermindering (p < 0.05) in die hoeveelheid grondbedekking, maar dieselfde behandeling het gelei tot ‘n toename (p < 0.05) in grondstikstof. Ten spyte van die vermindering in grondbedekking na benutting, was grond nog voldoende bedek volgens die standaarde van bewaringslandbou. Dit dui daarop dat die gebruik van dekgewasse 'n bykomende inkomste kan genereer en die ekonomiese lewensvatbaarheid van dekgewasproduksie kan verbeter.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106135
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