Developing management strategies to support sustainable production of lucerne in long-rotation cropping systems

Van der Westhuizen, Christoff George (2020-04)

Agronomy

Thesis

ENGLISH ABSTRACT: Lucerne (Medicago sativa L.) forms part of long-rotation cropping systems integrated with livestock in the southern Cape of South Africa. The lucerne phase is five to seven years long, followed by five to seven years of cash crops. Lucerne swards allow for the integration of livestock into cropping systems, improved resource utilisation, is a high-quality animal forage, biologically fix N, break disease cycles and may improve subsequent cash crops yields. However, some farmers consider excluding lucerne from crop production cycles. The main reasons for the exclusion of lucerne swards are low summer and winter herbage production due to moisture stress and lucerne’s natural winter dormancy. Low herbage production during these periods create considerable fodder flow deficits and make the management of fodder flow programmes challenging for farmers. The oversowing of dryland lucerne swards with annual winter growing forage crops, to create lucerne-based multiple species pastures, was investigated to determine if fluctuations in fodder flow programmes could be reduced through increased winter herbage production. Field experiments were conducted at Tygerhoek Research Farm (Riversonderend) during the 2018 and 2019 growing seasons. Both single species treatments and mixes were oversown into an existing lucerne base. Single species treatments included black oats, forage barley, stooling rye, Westerwolds ryegrass, forage radish and canola. Mixes consisted of various combinations of hybrid ryegrass, Italian ryegrass, forage barley, black oats, various annual Medicago and clover species, vetch and forage radish. The effect of oversown species and mixes on herbage production, pasture and soil quality was monitored for the duration of this study. Drought conditions after oversowing restricted the performance of the oversown species and mixes and had a knock-on effect that persisted for the duration of this trial. No treatment had a higher herbage yield to that of the control at any stage in the growing season (p>0.05). Small grains and mixes that contain small grains did however show the most potential to improve herbage production, especially in late winter. Due to poor performance of oversown treatments, herbage samples mainly consisted of the lucerne base and ryegrass, both as an oversown species and weed. The relatively similar species composition from different treatments yielded no clear and or obvious treatment that improved pasture quality, however, grazing management ensured that all treatments were of a high quality at the time of sampling. Similar returns of organic matter, both quantatively and qualitatively resulted in soil quality that was similar between all treatments. Different results may be obtained if oversown species establish well and this study should be replicated in years of normal rainfall distribution to fully comprehend how changes in pasture composition will affect herbage production and pasture quality. Soil physical, chemical and biological parameters should also be monitored over an extended period of time as changes in soil quality may take several years in Mediterranean climates.

AFRIKAANSE OPSOMMING: In die suid Kaap van Suid-Afrika word lusern (Medicago sativa L.) in langrotasie-wisselboustelsels ingesluit en laat vir boere toe om hul boerdery te diversifiseer met ’n veekomponent. Die lusern-fase is vyf tot sewe jaar lank en word opgevolg deur vyf tot sewe jaar van kontantgewasse. Lusern hou ’n verskeidenheid voordele in vir boere. Buitendien dat dit toelaat vir ’n veekomponent, laat lusern boere ook toe om hul hulpbronne meer effektief te gebruik. Dit verseker ’n hoë gehalte weiding vir diere, stikstoffiksering, verhoed die oordrag van siektes en kan lei tot hoër opbrengste van die daaropvolgende kontant gewasse. Ten spyte van die voordele, oorweeg boere steeds om lusern uit hul wisselboustelsels weg te laat. Dit is hoofsaaklik as gevolg van lusern se lae produksie in somer en winter. In die somer word produksie beperk deur droë toestande. In die winter sal koel en koue toestande produksie beperk weens lusern se natuurlike winterdormansie. Groot produksie woord fluktuasies maak dit moeilik vir boere om voervloeiprogramme effektief te bestuur. Die oorsaai van bestaande droëland lusernstande met eenjarige wintergewasse, om lusern-gebaseerde mengsels te vorm, is ondersoek om te bepaal of voervloeifluktuasies in die wintermaande verminder kan word. Veldproewe is uitgevoer op Tygerhoek proefplaas tydens die 2018 en 2019 groei seisoene. Enkelspesies as ook mengsels is in die bestaande lusern stand ingesaai. Enkelspesies het in gesluit swart hawer, voergars, stoelrog, Westerwolds raaigras, voerradys en canola. Mengsels het bestaan uit verskeie kombinasies van hibriede raaigras, Italiaanse raaigras, voergars, swart hawer, verskeie Medicago en klawerspesies, wieke en voerradys. Die invloed van die lusern-gebaseerde mengsels op produksie, weidingskwaliteit en grondkwaliteit is gemeet tydens hierdie studie. Buitengewone droë toestande na die oorsaai van die eenjarige wintergewasse het ’n deurlopende effek op die proef gehad. Geen behandeling het ’n hoër produksie as die kontrole gehad tydens enige tydperk in die groeiseisoen nie (p>0.05). Kleingrane en mengsels wat kleingrane bevat het, het egter die meeste potensiaal gewys, veral in laat winter. Die swak vestiging van die die oorgesaaide gewasse het daartoe gelei dat die spesiesamstelling soortgelyk was as gevolg van die groot lusern en raaigraskomponente. Die soortgelyke spesiesamestellings het verhoed dat daar onderskei kon word tussen behandelinge op ’n weidingskwaliteit vlak. Alle behandelings was egter van ’n hoë gehalte weidingskwaliteit toe monsters geneem is. Soortgelyke insette van organiese materiaal, beide in hoeveelheid en kwaliteit, het daartoe gelei dat daar geen verskille vir grondkwaliteit tussen enige behandferlings was nie. Indien eenjarige gewasse goed vestig mag resulte verskil van die wat in hierdie studie verkry is. Hierdie studie moet herhaal word in jare waar reënval meer normaal is om die ten einde verstaan hoe produksie, weidingskwaliteit en grondkwaliteit beïnvloed kan word. Grondfisiese, -chemiese en -biologiese parameters moet ook oor ’n langer tydperk gemeet word aangesien grondkwaliteit stadig verander in ’n Mediterreense klimaat.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108294
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