Phosphorus fertiliser source and its effect on potato (Solanum tuberosum L.) production

Ndou, Vhuthu (2017-12)

Thesis(MScAgric)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Potatoes are an essential component in the diet of millions of consumers in developing countries such as South Africa. Potatoes play a major role in national food security, nutrition, poverty alleviation and income generation through their role in the processing industries. The potato crop requires a lot of soil nutrients, particularly phosphorus (P) and low soil fertility is one of the major factors responsible for reduced crop yields. Polyphosphates are increasingly being favoured as inorganic P source used to increase crop productivity. In order to evaluate the response of potatoes to P sources and P application levels a series of pot experiments were conducted in the summer of 2015 and the winter of 2016, with the aim of evaluating the growth, yield and quality of potatoes in response to different P sources orthophosphate (mono-potassium phosphate – MKP) and polyphosphate with varying pH levels. In the first experiment conducted in the summer of 2015 four potato cultivars (Mondial, Sifra, Lanorma and Innovator) as prescribed by Potato South Africa were grown with different P sources. Treatments consisted of: T1) 100% orthophosphate, T2) 25% orthophosphate + 75% polyphosphate, T3) 50% orthophosphate + 50% polyphosphate and T4) 100% polyphosphate. This experiment was repeated in the winter of 2016 but using cultivars Eos and Destiny due to immediate availability. Morphological and yield parameters showed responses to P source, which was reflected during both seasons. In both seasons total tuber yield was highest when potato plants were fertilised with 100% orthophosphate. Phosphorus utilization efficiency (PUE) and tuber defects were not affected. Phosphorus-uptake efficiency was significantly different between cultivars in both seasons. Tuber and leaf analysis revealed that P applied as 50% polyphosphate showed high percentage of N content for tubers, and applying P as 100% and 50% polyphosphate resulted in higher P leaf content. Overall results of the two-season study show that orthophosphate had a superior effect on potato growth and yield compared to applying polyphosphates. To study the effect of pH on the uptake of P, potato plantlets (cultivar Mondial) were fertilised with: T1: Control – 100% of P applied as orthophosphate (mono-potassium phosphate) at pH levels 5.5, 6.5 and 7.5 and T2: P applied as polyphosphate at pH levels 5.5, 6.5 and 7.5. Results showed that interaction between P application and pH levels significantly influenced shoot dry mass and total yield. The orthophosphate showed higher shoot dry mass in comparison to the polyphosphate. Total fresh tuber yield was not affected by the pH of the solution when P was applied as orthophosphate. For most other parameters no difference was observed between the orthophosphates and polyphosphates and pH levels. Interaction effects between P treatments and pH levels for tuber and leaf analysis were however noted; polyphosphate at pH of 7.5 gave higher tuber N and Zn content, while the highest B content for tubers was obtained with orthophosphates, at pH 6.5. The overall results of the pH experiment showed that the orthophosphates and the polyphosphates did not differ in terms of crop yield. These results add valuable information for optimizing potato fertilisation to enhance productivity.

AFRIKAANSE OPSOMMING: Aartappels is 'n noodsaaklike komponent in die dieet van miljoene verbruikers in ontwikkelende lande soos Suid-Afrika. Aartappels speel 'n belangrike rol in die nasionale voedselsekerheid, voeding, armoedeverligting en inkomstegenerering deur middel van hul rol in die verwerkings-nywerhede. Die aartappelplant vereis baie voedingstowwe in die grond, veral fosfor (P) en lae grondvrugbaarheid is een van die belangrikste faktore wat verantwoordelik is vir verminderde oesopbrengste. Poli-fosfate word toenemend verkies as anorganiese P-bron waar dit gebruik word om produktiwiteit te verhoog. 'n Reeks pot eksperimente is uitgevoer in die somer van 2015 en die winter van 2016 om die reaksie van aartappels op P bronne en P toedieningspeile te evalueer. In die eerste eksperiment (somer 2015) is vier aartappelkultivars (Mondial, Sifra, Lanorma en Innovator) gekweek met verskillende P bronne. Behandelings het bestaan uit: T1) 100% ortofosfaat, T2) 25% ortofosfaat + 75% polifosfaat, T3) ortofosfaat 50% + 50% polifosfaat en T4) 100% polifosfaat. Hierdie eksperiment is herhaal in die winter (2016), maar kultivars Eos en Destiny is gebruik. Morfologiese parameters en opbrengs is beïnvloed deur die P behandelings in beide seisoene. In beide seisoene was die totale knolmassa die hoogste vir plante behandel met 100% ortofosfaat. Fosfor gebruik-doeltreffendheid (PUE) en knol defekte is nie beduidend beïnvloed nie. Fosfor-opname-doeltreffendheid het beduidend verskil tussen kultivars en tussen die twee seisoene. Knol- en blaarontledings het getoon dat knolle „n hoë persentasie N het wanneer P toegedien word as 50% polifosfaat. Daarteenoor was die P inhoud van die blare hoër wanneer P toegedien is as 100% en 50% polifosfaat. Algehele resultate van die studie oor die twee seisoene toon dat ortofosfaat n beter uitwerking op plant groei en aartappelopbrengs gehad het. Om die effek van pH op P opname te evalueer is aartappelplantjies (kultivar Mondial) behandel met: T1: kontrole - 100% P toegedien as ortofosfaat (mono-kaliumfosfaat) by pH 5.5, 6.5 en 7.5 en T2: P toegedien as polifosfaat by pH 5.5, 6.5 en 7.5. Resultate het ʼn interaksie getoon tussen P toediening en pH-vlakke op die halm droëmateriaal en die totale opbrengs. Vir ander parameters was geen verskil waargeneem tussen die P behandelings en pH-vlakke nie. Knol N en Zn inhoud was egter hoër waar polifosfaat by pH van 7.5 toegedien is, terwyl die hoogste B inhoud vir knolle gemeet is waar ortofosfate by pH 6,5 toegedien is. Hierdie resultate lewer waardevolle inligting vir die optimalisering van aartappel bemesting om produktiwiteit te verbeter.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102740
This item appears in the following collections: