Does zinc influence germination, vegetative growth or yield of wheat (triticum aestivum)?

Thesis (MScAgric)--Stellenbosch University, 2018.ENGLISH ABSTRACT: Nutrients are essential to all life on earth. Nutrients are divided into macro and micro-nutrients. Macro nutrients such as proteins and carbohydrates for example are needed by organisms in large quantities to remain healthy while micro nutrients such as vitamins and minerals for example are needed in very small quantities. A lack in sufficient uptake of either macro or micro nutrients by organisms can lead to serious health problems, due to the occurrence of nutrient deficiencies. Emphasis has been laid on the importance of zinc (Zn; a micro nutrient) as more than 50% of soils on which staple foods (e.g., wheat) are produced globally are considered as being Zn deficient. Various secondary advantages such as decreased emergence rate, increased disease resistance, better stand density and yield have been linked to an improvement in wheat vigour due to an increase in the Zn concentration [Zn], either in wheat seeds, in the soil or due to foliar applications of Zn. The main aim of the study was to determine what the causal effects of increased [Zn] are on these various parameters. The influence of seed [Zn], priming and foliar applications of Zn fertilisers were either studied in uncontrolled or controlled environmental conditions. Various stress aspects, including water stress, increased planting depth and weed competition were also incorporated into some of the controlled environmental experiments. It is noteworthy that no Zn deficient (< 22 mg kg-1) seeds were used during these experiments as none could be found. An increase in wheat seed [Zn] did have a significant positive influence (p < 0.05) on the germination percentage of wheat seeds during the germination experiment. Soil moisture and planting depth had a significant influence on seedling growth (p < 0.05). Seemingly, insufficient amounts of soil moisture led to decreased seedling growth while an increase in planting depth led to a decrease in seedling emergence. Wheat seed emergence was also significantly (p < 0.05) improved due to an increase in wheat seed [Zn]. Wheat seed germination and seedling growth was not influenced by the presence of ryegrass, but the presence of only one wheat plant had a significant influence on the dry mass (DM) production of ryegrass (p < 0.05). Wheat stem length and DM actually increased in one of the experiments as the number of wheat plants decreased and the number of ryegrass plants increased. This finding was corroborated by other similar studies and also by two of the controlled environmental condition experiments in this study. Seed [Zn] and different fertilizer treatments had an indifferent influence on plant growth and nutrient composition at all three localities where field trails were conducted. Results were inconclusive as to whether seed [Zn] did have a positive influence on growth and vigour of wheat, which may have been attributed to the absence of truly Zn deficient wheat seeds in this instance.AFRIKAANSE OPSOMMING: Nutriënte is noodsaaklik vir die bestaan van alle lewende organismes op aarde. Nutriënte word verdeel in makro- of mikronutriënte. Makro nutriënte soos bv proteine en koolhidrate word in groot hoeveelhede benodig deur organismes om gesond te bly terwyl mikro nutriënte soos bv vitamienes en minerale slegs in klein hoeveelhede benodig word. 'n Gebrek aan voldoende opnames van makro- of mikronutriënte deur organismes kan ernstige gesondheidsprobleme veroorsaak weens voedingstekorte. Klem word tans gelê op die belangrikheid van sink (Zn; 'n mikronutriënt) aangesien meer as 50% van grond, waarop stapelvoedsels (byvoorbeeld koring) wêreldwyd geproduseer word, beskou word as gronde met ‘n tekort aan Zn. Verskeie sekondêre voordele soos vinniger saailing opkoms, verhoogde siekteweerstand, beter plantdigtheid en opbrengs is gekoppel aan 'n verhoging in koring se lewenskragtigheid as gevolg van 'n toename in die Zn konsentrasie [Zn]. Hierdie verhoogde [Zn] kan deur verskeie metodes bereik word insluitend, om gebruik te maak van koringsaad met hoë [Zn], om te plant op gronde met hoë [Zn] of deur gebruik te maak van blaar voedingsstowwe wat Zn bevat. Die hoofdoel van die studie was dus om te bepaal wat die werklike effek van verhoogde [Zn] op hierdie verskillende parameters is. Die invloed van saad [Zn], “priming” en blaar toedienings van Zn bevattende kunsmis was onder beheerde of onbeheerde omgewingstoestande ondersoek. Die invloed van verskeie stremmingsaspekte soos waterstremming, verhoogde saad plantdiepte en onkruidkompetisie is ook in sommige van die beheerde omgewings eksperimente ondersoek. Dit moet genoem word dat geen ware Zn gebrek ([Zn] < 22 mg kg-1) saad tydens hierdie eksperimente gebruik is nie bloot as gevolg van die feit dat geen sulke saad opgespoor kon word nie. 'n Toename in koringsaad [Zn] het gedurende die ontkiemingseksperiment 'n beduidende positiewe invloed (p < 0.05) op die ontkiemingspersentasie van die koringsaad gehad. Grondvog en plantdiepte het 'n beduidende invloed op saailinggroei gehad (p < 0.05). Dit is vanselfsprekend dat onvoldoende hoeveelhede grondvog tot verlaagde saailinggroei gelei het, terwyl 'n toename in plantdiepte gelei het tot 'n afname in saailing opkoms. Koringsaad opkoms is ook aansienlik (p < 0.05) verbeter as gevolg van 'n toename in koringsaad [Zn]. Koringsaad ontkieming en saailing groei is nie beïnvloed deur die teenwoordigheid van raaigras nie, maar die teenwoordigheid van slegs een koringplant het 'n beduidende invloed gehad op die droëmassa-produksie van raaigras (p < 0.05). Koring stamlengte en droëmassa het eintlik in een van die eksperimente toegeneem namate die aantal koringplante afgeneem het en die aantal raaigras plante toegeneem het. Hierdie bevinding word nie net deur verskeie ander wetenskaplikes ondersteun nie, maar is bevestig in twee van ons beheerde omgewingseksperimente. Koringsaad se [Zn] en die gebruik van verskillende kunsmisbehandelings het selde 'n beduidende invloed op plantegroei en die samestelling van voedingstowwe in die saad gehad by al drie lokaliteite waar veldproewe plaasgevind het. Ons neem aan dat 'n toename in saad [Zn] 'n positiewe invloed op die groeikragtigheid van koring het, maar dit was nie duidelik tydens hierdie proewe nie as gevolg van die afwesigheid van koringsaad wat werklik ‘n Zn tekort het