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3.3 Factors affecting yield response to fertilizers 21
3.3.1 Variety 21
3.3.2 Planting density 22
3.3.3 Previous cropping 22
3.3.4 Soil nutrient content 22
3.3.5 Soil moisture 22
3.3.6 Farmyard manure 26
3.3.7 Duration of experiments 26
4 Effects of fertilizers on quality 26
4.1 Superficial properties of tubers 26
4.1.1 Tuber size 26
4.1.1.1 Nitrogen 27
4.1.1.2 Phosphate 28
4.1.1.3 Potassium 28
4.1.1.3.1 Form of potash fertilizer 28
4.1.1.4 Magnesium 29
4.1.2 Tuber weight 29
4.1.3 Mechanical damage to tubers 30
4.1.3.1 Effect of nitrogen 30
4.1.3.2 Effect of phosphorus 30
4.1.3.3 Effect of potassium 30
4.1.4 Tuber colour (internal blackening) 31
4.1.4.1 Effect of nitrogen 31
4.1.4.2 Effect of phosphorus 32
4.1.4.3 Effect of potassium 32
4.1.4.3.1 Effect of form of potash 34
4.2 Tuber composition 35
4.2.1 Dry matter content 35
4.2.1.1 Effect of nitrogen 35
4.2.1.2 Effect of phosphorus 36
4.2.1.3 Effect of potassium 36
4.2.1.3.1 Effect of form of potash 38
4.2.1.4 Effect of magnesium 38
4.2.2 Starch content 38
4.2.2.1 Effect of nitrogen 38
4.2.2.2 Effect of phosphorus 41
4.2.2.3 Effect of potassium 41
4.2.2.3.1 Effect of form of potash 43
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