Optimizing harvesting procedures of Amaranthus hybridus L. and A. tricolor L. under different watering regimes during hot and cool seasons in southern Mozambique

Ribeiro, Jeronimo E.M.M. (2017-03)

Thesis (PhD)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Drought has been the major constraint for vegetable and food crop production in arid and semi-arid regions as is the case in southern Mozambique with a tropical dry savanna climate that is prone to droughts. In this vulnerable region, malnutrition associated with scarcity of vegetables imposed a serious constraint in the diet of rural communities. Rural communities are forced to use wild plants, such as amaranth, as a way to supplement their nutrition. Here Amaranth species grow naturally and the leaves are regularly collected manually to be consumed as tender greens. There is no evidence of grain consumption. Although few growers cultivate amaranth in small areas or in their gardens, the intensity and frequency with which the leaves are collected has not been tested yet. The production of multi-purpose amaranth, a C4 plant widely distributed in the tropics and relatively drought-tolerant crop, offer a great potential to play a beneficial role in nutrition and food security. Three field experiments with Amaranthus hybridus and A. tricolor repeated six times each (three during the rainy season and three in the dry season) were carried out during the period from December 2013 to October 2015 in Maputo. A randomized complete block design in a factorial arrangement was used in each experiment. Experiment one aimed to assess the vegetative growth, flowering, leaf and grain yields, as well as nutrient contents in leaves and grain of those species when subjected to watering regimes of 80%, 50% and 20% of total available water. The relationship between temperature and day length on the leaf yield and the time to flowering were also assessed (Chapters 3 and 4). The treatments were laid out in a 3 x 2 factorial arrangement with six replications. In experiments two (Chapther 5) and three (Chapter 6), under the same watering regimes and with the same species, the vegetative growth, leaf yield and nutrient content were assessed as affected by harvesting intensity (plants topped by 25% and 50% of their heights) and harvesting frequency (every two weeks and every three weeks) respectively. In these two experiments, the treatments were laid out in a 3 x 2 x 2 factorial arrangement with three replications. Results from experiment one revealed that vegetative and reproductive growths were sensitive to soil water contents of 50% and 20% of total available water. However, the vegetative growth was less susceptible to water deficits that occurred in short intervals throughout the rainy season. Higher calcium and crude protein contents in the leaves were found at low water levels with the highest values obtained in A. tricolor. Temperature significantly affected the high leaf yield during the rainy season while day length had a noticeable influence on the low leaf yield during the dry season. The onset of flowering was determined by day length and minimum temperature with day length the most determining factor. The vegetative growth of both species showed similar behavior in response to different soil water and climate conditions over the year. The highest grain yield and harvest index was obtained in A. tricolor with an increase in minimum temperature which delayed flowering mainly when the day length was above 12 hours day-1 during the rainy season. The results from experiment two and three indicated insufficient evidence to support the hypothesis that the combined effects of watering regimes and harvesting intensity, and watering regimes and harvesting frequency affect vegetative growth in both species. However, the vegetative growth of both species was tolerant to water deficit at 50% of total available water with successive cuttings. The best harvesting intensity and frequency found was 25% of their heights and two-week intervals respectively, since this frequency yielded more small and tender green leaves which are preferred by the consumer. Amaranthus hybridus showed better performance and higher leaf yield compared to A. tricolor over the year. Results also revealed that the multiple harvests extend the vegetative growth phase which is an advantage for amaranth leaf production, especially under short days during the dry season. In plants harvested several times, the calcium and crude protein were not affected by watering regimes. However, the highest calcium and crude protein content in the leaves were obtained at final and first harvests respectively. As a leafy vegetable, A. hybridus showed to have potential to become a suitable crop throughout the year and to supplement calcium and protein requirements in the diet of rural communities. It is recommended to be cultivated in the rainy season under rain-fed condition with supplemental irrigation and in the dry season as an irrigated crop at 50% of total available water. In both seasons, the leaf harvesting should be topping by 25% at 2 weeks intervals.

AFRIKAANS OPSOMMING: Droogte is die belangrikste beperkende faktor vir voedselproduksie in ariede en semi-ariede gebiede soos in Suid- Mosambiek wat ‘n droë tropiese savanna klimaat het wat aan gereelde droogtes onderwerp word. In hierdie kwesbare gebied is wanvoeding as gevolg van ‘n gebrek aan voldoende groenteproduksie ‘n ernstige beperking in die diet van landelike gemeenskappe. Landelike gemeenskappe word dus gedwing om wilde plante soos amarante te verbruik om voedingsbehoeftes aan te vul. Amarantspesies groei wild hier en die blare word gereeld versamel om as vars groente geëet te word. Daar is geen getuienis dat amarantplante se saad gebruik word as voedsel nie. Alhoewel ‘n paar produsente anmarant in klein gebiede of in hulle tuine verbou, is daar nog geen navorsing gedoen om die optimum frekwensie en intensiteit van die oesproses van die blare te bepaal nie. Die produksie van die meerdoelige amarant, ‘n C4 plant wat wydverspreid in die trope voorkom en ‘n redelike droogtebestande gewas is, toon groot belofte om ‘n groot rol te speel in voedselsekerheid en voeding. Drie veldproewe met Amaranthus hybridus en A. tricolor wat ses keer herhaal is (drie keer gedurende die reënseisoen en drie keer tydens die droë seisoen) is uitgevoer gedurende die periode van Desember 2013 tot Oktober 2015 in Maputo. ‘n Volledig ewekansige blokontwerp is in alle proewe gebruik. Eksperiment een se doel was om die vegetatiewe en reproduktiewe groei sowel as die blaar- en graankwaliteit van die betrokke spesies te bepaal wanneer dit blootgestel is aan waterpeile van 80%, 50% en 20% van totale beskikbare water. Die verhouding tussen temperatuur en daglengte en die invloed daarvan op die blaaropbrengs en tyd tot blomvorming is ook ondersoek (Hoofstukke 3 en 4). Die behandelings is gereël as ‘n 3 x 2 faktoriaal uitleg met ses herhalings. In Eksperimente twee (Hoofstuk 5) en drie (Hoofstuk 6), onder dieselfde waterbehandelings met dieselfde spesies, is die vegetatiewe groei, blaaropbrengs en nutriëntinhoud se reaksie op oesintensiteit (plante gesny met 25% en 50% van hulle hoogtes) en oesfrekwensie (elke twee weke en drie weke) onderskeidelik, gemeet. In hierdie twee eksperimente is die behandelings toegepas as ’n 3x2x2 faktoriaal gereëlde eksperiment met drie herhalings. Resultate van Eksperiment 1 het gewys dat vegetatiewe en reproduktiewe groei sensitief was vir grondwatervlakke van 50% en 20% van totale beskikbare water. Die vegetatiewe groei was egter minder vatbaar vir kort periodes van watertekorte wat gedurende die reënseisoene voorgekom het. Hoër kalsium en ruproteien vlakke in die blare het voorgekom by lae watervlakke en die hoogste waardes het voorgekom in A. tricolor. Die hoë blaarproduksie tydens die reënseisoen is betekenisvol beïnvloed deur temperatuur terwyl die heelwat laer blaarproduksie tydens die droë seisoen betekenisvol deur daglengte beïnvloed is. Die aanvang van blomvorming is bepaal deur daglengte en minimumtemperature met daglengte die mees bepalende faktor. Die vegetatiewe groei van beide spesies het dieselfde tendense getoon in reaksie op die verskillende grondwater en klimaatstoestande deur die jaar. Die hoogste graanopbrengs en oesindeks is waargeneem in A. tricolor met ‘n toename in minimum temperature wat blomvorming hoofsaaklik onderdruk het wanneer die daglengte bo 12 ure per dag was tydens die reënseisoen. Die resultate van Eksperimente twee en drie het nie genoegsame getuienis gelewer om die hipotese te ondersteun dat die gekombineerde effek van watervlakke in die grond en oesintensiteit, asook watervlakke en oesfrekwensie die vegetatiewe groei van beide spesies affekteer nie. Die vegetatiewe groei van beide die spesies was egter redelik verdraagsaam vir ‘n watertekort van 50% van totale beskikbare water wanneer hulle herhaaldelik gesnoei is. Die beste oesintensiteit en oesfrekwensie is gevind wanneer die boonste 25% afgeknip is en tweeweekliks geknip is respektiewelik omdat hierdie betrokke oesfrekwensies en oesintensiteite meer klein en sagte blaartjies voortbring wat deur verbruikers verkies word. Amaranthus hybridus het beter presteer en meer blare geproduseer deur die twee jaar as A. tricolor. Die resultate het ook getoon dat meervoudige oeste die vegetatiewe groeifase verleng het wat voordelig is vir amarant blaarproduksie, veral tydens kort dae gedurende die droë seisoen. In plante wat ‘n paar keer agtereenvolgens geoes is, is die kalsium- en ruproteienvlakke nie deur die waterbehandelings beïnvloed nie. Die hoogste kalsium en ruproteienvlakke is egter in die blare gevind tydens die eerste en finale oesdatums respektiewelik. Samevattend kan dus gesê word dat A. hybridus, as ‘n blaargroente, die potensiaal het om ‘n geskikte gewas te word wat deur die jaar produseer en die kalsium- en ruproteieninhoud kan bydra om die kalsium- en ruproteienvereistes in die diëte van landelike gemeenskappe te bevredig. Dit word aanbeveel om in die reënseisoen onder droëlandtoestande met bykomende besproeiing en in die droë seisoen as besproeide gewas teen 50% van totale beskikbare water verbou te word. In beide seisoen behoort blaaroes plaas te vind teen verwydering van 25% van die hoogte van die plant elke twee weke.

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