1 markAgriculturalists in Mozambique investigated the optimum planting conditions for sweet potato plants. Sweet potato (Ipomoea batatas) is a popular root crop, with increasing use as a staple vegetable. Variables under investigation were the spacing of seed sowing and the optimum use of fertilisers to achieve a maximum yield.
Plant spacing (16, 20 and 25 cm between plants) was combined with three nitrogen addition rates of 30, 35 and 40 grams per square metre (gm-2) in separate test plots of area 1.5m2. The source of nitrogen used in the study was urea (CH4N2O). Other growing conditions were kept constant, to determine the optimal combination of spacing and nitrogen addition.
The study ran for 175 days after planting individual I. batatas seeds in the respective conditions. The results of the study are summarised in the table below.
Identify the growth conditions that gave the most favourable yield of sweet potatoes in this study.
1 markDescribe the relationship between the mean underground dry mass of the crop and the mean crop yield of sweet potatoes in this study.
3 marksCompare and contrast the effects of increasing spacing and increasing urea addition, in terms of underground dry mass and crop yields.
2 marksSuggest, with a reason, why the choice of units of crop yield quoted in this study (tonnes per hectare) was not an appropriate one.
4 marksIn another part of this investigation, the mass of plant matter above ground (both fresh mass and dry mass) was measured against leaf length and crop yield for the three levels of urea concentration previously tested. All these data were gathered from sweet potato plants spaced at 20cm distance. The results are shown in the graph below.
The scientists concluded that a planting regime of plants spaced 20cm apart with an addition of urea more than 35 gm-2 should be recommended to farmers. Evaluate the scientists' conclusion, using the data above and from part a).
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