Mulching and tillage with compost to improve poor performing grapevines

Thesis (MScAgric)--Stellenbosch University, 2017.ENGLISH SUMMARY: The study explored two strategies for improvement of grapevine performance. The first aim was to assess varying levels of compost mulch thickness and the effects thereof on soil water content and grapevine performance as well as to determine whether mulching can be recommended as a watersaving practice under the given conditions. The second aim was to investigate the effect of incorporating organic matter during the root pruning action and with a furrow plough, on the soil environment and grapevine performance. Where spatial variability in sloped or terraced vineyards is a concern, application of compost as a mulch to the grapevine row is impractical. A clear understanding of whether or not incorporating compost proves to have substantial benefits to soil water infiltration and retention, as well as grapevine performance, would be of value to the wine industry. Two methods of organic matter incorporation were compared, namely the furrow plough and deep tillage or root pruning. In the first experiment, compost mulch was applied on the grapevine row at varying thicknesses in a Shiraz/101-14 Mgt vineyard near Stellenbosch. Results showed that the application of compost mulch to a thickness of 16 cm had no effect on soil water content to a depth of 90 cm compared to the bare soil. While greater fluctuations in soil water content occurred in the 0-30 cm layer, the treatments did not differ with respect to soil water content over the two seasons. However, water infiltration rate increased with mulch thickness, i.e. the highest infiltration rate was observed in the soils under the thicker mulches. Nevertheless, the thicker mulches, i.e. 8 cm and 16 cm, appeared to intercept rainfall when relatively small events occurred. Under the prevailing conditions, the mulch was not effective in maintaining a higher soil water content on the grapevine row compared to bare soil. Grapevine water constraints were also not affected by compost mulch, regardless of the thickness. However, vegetative growth and yield responded positively to mulch thickness over the two seasons. Since water constraints did not differ in response to mulch thickness, improved water uptake was not considered to have contributed to the improved growth and yield. Fine root development observed in the shallow soil layers under the mulches could have contributed to the growth response by allowing for improved nutrient absorption. The mulch had weathered substantially after two years, which was attributed to the maturity of the compost and the quantity of fine material. In the second experiment, compost was incorporated using a furrow plough during the root pruning action, and compared to a no-till and no compost control, as well as root pruning without compost. The treatments were applied in every, and in alternate rows in a terraced Pinotage/R110 vineyard near Stellenbosch. Compost incorporation by means of the furrow plough and root pruning, increased water infiltration rate compared to the control. Root pruning without compost also tended to increase infiltration rate. Higher infiltration rates are expected to reduce water loss by runoff and increase in the amount of water entering the soil. However, the tillage and compost treatments had no effect on the soil water content on the grapevine row. It would seem that there was limited lateral flow of water from the work row to the grapevine row. After two years, the furrow plough with compost and root pruning with and without compost reduced penetration resistance up to 15 cm and 45 cm, respectively. The lower penetration resistance in the soil where compost was incorporated using the furrow plough could be attributed to a slightly higher soil water content in that layer where the compost was concentrated. The penetration resistance in the soil of the control exceeded the 2000 kPa threshold for inhibited root growth at a depth of 12 cm. The soil loosening action of the root pruning with compost is expected to allow for improved root development to a greater depth than the furrow plough treatment. However, the furrow plough treatment may have encouraged root development between the tractor wheel tacks to a depth of 15 to 20 cm. Root pruning per se had no effect on the soil chemical status, but decreased compaction. Where compost was added, the soil pH increased, probably due to the high amount of calcium in the compost and the dissolution of organic acids present in the organic material. The compost also tended to increase magnesium, potassium and sodium as well as organic carbon and phosphorus in the soil, particularly in the shallow layers. The potassium and phosphorus could be a source of nutrients to the grapevines, while the organic carbon influences the accumulation of soil organic matter. Although the amount of sodium in the soil increased, the extractable sodium percentage was in fact reduced in the 0-15 cm soil layer, due to the high amount of calcium. The extractable sodium percentage was also well below the threshold where sodicity problems would be expected. Under the prevailing conditions, root pruning did not seem to have a positive effect on grapevine vegetative growth and yield. Rainfall during the study was appreciably lower than the long term mean, particularly in 2015. As a result of dry soil conditions the degree of root regeneration in the loosened soil and the subsequent grapevine responses may have been affected. In contrast, where compost was incorporated during the root pruning action, growth and yield increased over two consecutive seasons. Likewise, where compost was incorporated in furrows, it also had a positive effect on growth and yield. It appeared that root pruning in every row with compost did not provide significant additional benefits to growth and yield compared to the root pruning in alternate rows with compost. Apart from the slightly higher pH and lower colour in the wines of the compost treatments in the first year, juice and wine quality characteristics were not affected by any of the tillage or compost treatments. The higher potassium content in the soils measured two years after the compost was applied appeared to have had no effect on juice and wine quality. Cover crop growth also responded positively to the addition of compost. It is interesting to note that the enhanced cover crop performance did not appear to compete with the grapevines. Decomposition and mineralisation of the cover crop residue in the vineyard would be expected to further improve organic matter and nutrient accumulation in the soils where cover crop dry matter production was high.AFRIKAANS OPSOMMING: Die studie het twee strategieë ondersoek vir die verbetering van wingerdstokprestasie. Die eerste doelwit was om wisselende diktes komposdeklaag en die effekte daarvan op grondwaterinhoud te meet en wingerdprestasie, sowel as te bepaal of deklae aanbeveel kan word as 'n waterbesparingspraktyk in die heersende omstandighede. Die tweede doel was om die effek van organiese materiaal wat tydens ‘n wortelsnoei aksie of met 'n vlekploeg ingewerk is, op die grondomgewing en wingerdstokprestasie te ondersoek. Waar ruimtelike variasie in skuins of geterrasseerde wingerde groot is, is die toediening van ʼn komposdeklaag op die wingerdstokry onprakties. 'n Beter verstaan van die inkorporering van kompos aansienlike voordele inhou vir grondwater infiltrasie en -behoud, asook wingerdprestasie, sou waarde inhou vir die wynbedryf. Twee metodes van organiese materiaal inkorporering is vergelyk, naamlik die vlekploeg en diepbewerking of wortelsnoei. In die eerste eksperiment is ʼn komposdeklaag toegedien op die wingerdstokry teen verskillende diktes, in 'n Shiraz/101-14 Mgt wingerd naby Stellenbosch. Resultate het gewys dat die toediening daarvan op die wingerdstokry tot 'n dikte van 16 cm geen effek op grondwaterinhoud gehad het tot 'n diepte van 90 cm, in vergelyking met kaal grond. Groter skommelinge in grondwaterinhoud het in die 0-30 cm laag voorgekom, maar die behandelings het nie verskil met betrekking tot grondwaterinhoud oor die twee seisoene nie. Water infiltrasietempo het egter toegeneem met deklaagdikte, d.w.s. die hoogste infiltrasietempo was in die gronde met dikker deklae waargeneem. Nietemin, die dikker deklae, d.w.s. 8 cm en 16 cm, het oënskynlik reënval onderskep wanneer dit min gereën het. Onder die heersende omstandighede was die deklaag nie effektief in die handhawing van 'n hoër grondwaterinhoud op die wingerdstokry, in vergelyking met kaal grond nie. Wingerdstok watertekorte was ook nie beïnvloed deur die kompos deklaag nie, ongeag die dikte. Vegetatiewe groei en opbrengs het egter positief reageer op deklaag dikte oor die twee seisoene. Aangesien watertekorte nie reageer het op deklaagdikte nie, is dit onwaarskynlik dat beter wateropname bygedra het tot die beter groei en opbrengs. Fynwortelontwikkeling wat in die vlak grondlae onder die deklae waargeneem is, kon bygedra het tot die groeireaksie deur beter voedingstofopname te fasiliteer. Die deklaag het kwaai verweer na twee jaar, wat aan die volwassenheid van die kompos en die hoeveelheid fyn materiaal toegeskryf kan word. In die tweede eksperiment, is kompos ingewerk met behulp van 'n vlekploeg tydens ʼn wortelsnoeiaksie, wat vergelyk is met geen bewerking en geen kompos byvoeging, asook wortelsnoei sonder kompos. Die behandelings is in elke, asook in alternatiewe rye in 'n geterrasseerde Pinotage/R110 wingerd naby Stellenbosch toegepas. Kompos inkorporering met ʼn vlekploeg en tydens wortelsnoei, het waterinfiltrasietempo verhoog in vergelyking met die kontrole. Wortelsnoei sonder kompos het ook geneig om infiltrasietempo te verhoog. Hoër infiltrasietempos kan moontlik waterverlies deur afloop verminder en grondwaterinhoud verhoog. Die bewerking en komposbehandelings het egter geen effek op die grondwaterinhoud gehad op die wingerd ry. Dit lyk asof daar beperkte laterale vloei van water vanaf die werkry na die stokry was. Na twee jaar het die vlekploeg met kompos en wortelsnoei met en sonder kompos die grondpenetrasieweerstand tot op dieptes van 15 cm en 45 cm onderskeidelik verminder. Die laer penetrasieweerstand in die grond waar kompos geïnkorporeer is met behulp van die vlekploeg kan moontlik toegeskryf word aan 'n effens hoër grondwaterinhoud in die laag waar die kompos gekonsentreer was. Die penetrasieweerstand in die grond van die kontrole het die 2000 kPa drempelwaarde vir optimale wortelgroei op 'n diepte van 12 cm oorskry. Dit was verwag dat die grondlosmaakaksie van die wortelsnoei met kompos beter wortelontwikkeling tot 'n groter diepte sou toelaat as die vlekploeg behandeling. Die vlekploeg behandeling het egter wortelontwikkeling tussen die trekker wiel spore aangemoedig tot 'n diepte van 15 tot 20 cm. Wortelsnoei het geen effek op die grond chemiese status gehad nie, maar grondkompaksie het afgeneem. Waar kompos ingerwerk is, het die grond pH toegeneem, waarskynlik as gevolg van die hoë inhoud van kalsium in die kompos en die ontbinding van organiese sure in die organiese materiaal. Die kompos was ook geneig om magnesium, kalium en natrium asook organiese koolstof en fosfor in die grond te vermeerder, veral in die vlak grondlae. Die kalium en fosfor kan 'n bron van voedingstowwe vir die wingerdstokke wees, terwyl die organiese koolstof die aansameling van organiese materiaal beïnvloed. Hoewel die hoeveelheid natrium in die grond verhoog het, het die ekstraheerbare natriumverhouding verminder in die 0 15 cm grondlaag as gevolg van die hoë vlakke van kalsium. Die ekstraheerbare natriumverhouding ontledings was ook goed onder die drempel waar natriumbrak probleme verwag sou word. In die proef kondisies het wortelsnoei nie 'n positiewe uitwerking op wingerd vegetatiewe groei en opbrengs gehad nie. Reënval tydens die studie was merkbaar laer as die langtermyn gemiddelde, veral in 2015. As gevolg van droë grondtoestande, kon die graad van wortelgroei in die los grond en die daaropvolgende wingerd reaksies beïnvloed gewees het. In teenstelling, waar kompos geïnkorporeer was gedurende die wortelsnoei aksie, het groei en opbrengs oor twee opeenvolgende seisoene verhoog. Net so, waar kompos geïnkorporeer is in vlekvore, was daar ook 'n positiewe effek op groei en wingerd opbrengs. Dit lyk nie asof wortelsnoei in elke ry met kompos aansienlike bykomende voordele tot groei en opbrengs gehad het nie, in vergelyking met wortelsnoei in alternatiewe rye met kompos. Afgesien van die effens hoër pH en laer kleur in die wyne van die komposbehandelings in die eerste jaar, was sap en wyngehalte eienskappe nie geraak deur enige van die bewerking of komposbehandelings nie. Die hoër kaliuminhoud in die grond twee jaar nadat die kompos toegedien was het ook geen merkbare effek op sap en wyngehalte gehad nie. Dekgewas groei het ook positief reageer tot die byvoeging van kompos. Dit is merkwaardig dat die verbeterde dekgewasprestasie waarskynlik nie met die wingerdstokke kompeteer het nie. Waar degewas groei goed was, sou afbraak en mineralisasie van die dekgewasreste in die wingerd waarskynlik organiese materiaalinhoud en voedingstofaansameling verder verbeter