**10.2 Methods of planting**

Sweet potato is established mostly by planting vine cuttings, while the high-tech method of plug transplanting is practised in South Korea [48].

#### *10.2.1 Planting vine cuttings*

Prior to planting, vine cuttings can be dipped in fungicide solutions for 15 minutes to kill the pathogens, if any. The field is flush irrigated before planting for irrigated crops, while the vine cuttings are planted on a rainy day or just after rains for rain-fed crops.

The most common method planting is by burying the middle part of the vine cutting into the soil, leaving the two cut ends exposed to the air [45]. A notched stick can be used to push the cuttings into the soil. Some farmers plant by burying half of

*Sweet Potato (*Ipomoea batatas *(L.) Lam): A Review of Modern Varieties and Production… DOI: http://dx.doi.org/10.5772/intechopen.106586*

the cutting into the soil in an inclined position and exposing the other half to the air. Still others bury horizontally into the soil long cuttings with 5–6 nodes [48]. Depth of planting varies between 2.5 cm and 10.0 cm.

#### *10.2.2 Plug transplanting*

High-quality sweet potato plug seedlings are produced in bubble trays by using single node cuttings or shoot tip cuttings taken from virus-free mother plants under controlled environment [48]. This method is highly efficient in terms of time and labour use. Plug transplants are transplanted directly into the main field by a transplanter. High yields of storage roots are obtained by this method [51].

### **11. Water conservation and management**

An adequate and well-distributed rainfall and/or irrigation water is needed to get high sweet potato yields.

#### **11.1 Water requirement of sweet potato**

Like any other crop, water requirements of sweet potato are location-specific due to variations in climate, soil type, crop varieties, and other crop-growing conditions [52]. Water use efficiency (WUE) of a crop is defined as the total biomass produced per unit area and per unit of water used up in evapotranspiration of the crop (ETc) [53]. WUE is used to quantify agricultural productivity of crops in any area, specifically in water-stressed areas.

Being a drought-tolerant crop, sweet potato is more efficient in using limited available water than non-drought-tolerant crops [54, 55]. Drought tolerance in sweet potato is related more to its survival and fast recovery after dry spells than to yield potential under drought conditions [56]. Sweet potato's sensitivity to water stress varies with growth stages. Although, at establishment phase, sweet potato rooting is optimal at a soil moisture content of 80% of field capacity, substantial rooting occurs even at 40% of field capacity [57]. Prolonged drought at storage roots initiation and bulking stages reduces crop yields drastically.

#### **11.2 Irrigation management**

Proper scheduling of irrigation as per crop demand at different growth stages is critical to maintain high WUE [58]. In-field water conservation practices such as soil cover to reduce evaporation losses, precise supply of water at the root zone as in drip irrigation and crop-need-based nutrient management to enhance yields will all help increase WUE. In South Africa and Ethiopia, irrigation at 60% and 100% ETc produced root yields that are not significantly different; it implies that deficit irrigation to meet the 60% ETc of the crop can be recommended under water-scarce conditions [59, 60]. As a thumb rule, sweet potato crops require 2 millimetres (mm) of water per day during the establishment phase, and it can be gradually increased to 5–6 mm per day during the critical storage root initiation and bulking stages [61].

In practice, soil is moistened with a flush irrigation before planting so as to ensure sufficient soil moisture for proper sprouting and establishment of the vine cuttings after planting. The second irrigation is scheduled at 3 DAP, and then the crop is

irrigated at 7–10 days intervals. The irrigation is stopped 7–10 days before harvesting. Excess moisture must be avoided to prevent excessive vegetative growth at the expense of storage roots formation [62, 63], while water stress must be prevented through regular or supplemental irrigation during the most critical stages of storage root initiation, early bulking and late bulking in order to maximize root yields [64].

#### **11.3 Rainfall management**

Adequate amount and good distribution of rainfall during the entire crop growing period are critical for high yields of rain-fed crops. If the soil is dry during planting, the planted vine cuttings will dry up, resulting in poor crop establishment. Water stress or drought at storage roots initiation and bulking stages decreases leaf area index, increases metabolic toxicity and reduces yields [65]. Supplemental irrigation will save crops from droughts at critical crop growth stages.

Developing rainwater-harvesting structures such as farm ponds, small community reservoirs or check dams can help mitigate both drought and flooding impacts on rain-fed sweet potato crops by collecting and storing rainwater from peak floods and using it for supplemental irrigation of crops during periods of drought [66]. Providing supplemental irrigation from in-field water harvesting structures increased sweet potato yields significantly [67]. In India, rainwater harvesting structures, which are refilled during monsoons, reduce runoff by 40% and soil losses by 50%, and increase cropping intensity by 180% [68, 69]
