Introduction

In terms of global production, potato (Solanum tuberosum L.) is the fourth most important food crop after corn, rice and wheat. This crop is grown throughout the world. Present world production is some 321 million tons fresh tubers from 19.5 million ha.

Asia and Europe are the world’s major potato producing regions, accounting for more than 80% of world production. China is now the biggest potato producer, and almost a third of all potatoes are harvested in China and India. North America was the clear leader in productivity, at more than 40 tons per hectare. Asian consumption represents almost half of the world’s potato supply, but its huge population means that yearly consumption per person was a modest 25 kg in 2005. The heartiest potato eaters are Europeans. In Latin America and Africa consumption per capita is lowest, but increasing.

The potato plays a strong role in developing countries with its ability to provide nutritious food for the poor and hungry. The demand for potato is growing as both a fresh and processed food. The decreasing availability of land for area expansion means that yields will have to be improved. Critical to achieving improved tuber yields will be access to an adequate water supply, including more efficient use of scarce water and costly fertilizer inputs.

Potato is grown in about 100 countries under temperate, subtropical and tropical conditions. The potato is basically a crop of temperate climates. Yields are affected significantly by temperature and optimum mean daily temperatures are 18 to 20°C. In general a night temperature of below 15°C is required for tuber initiation. Optimum soil temperature for normal tuber growth is 15 to 18°C. Tuber growth is sharply inhibited when below 10°C and above 30°C. Cool conditions at planting lead to slow emergence which may extend the growing period. Tuber yield decreases with reduced sunshine hours per day. Potato varieties can be grouped into early (90 to 120 days), medium (120 to 150 days) and late varieties (150 to 180 days). Improved varieties include Russet Burbank, Desiree, Yukon Gold and Nicola, among others.

Potato requires a well-drained, well-aerated, porous soil with pH of 5 to 6. Compacted soils affect root penetration, water and nutrient uptake and tuber enlargement. The crop is moderately sensitive to soil salinity with yield decrease at different levels of ECe. ECe is the electrical conductivity of a saturated soil paste extract. The plant spacing is 0.75 m to 0.90 m between rows and 0.15 m to 0.3 m between plants under irrigated conditions, while sowing depth is generally 5 to 10 cm. Cultivation during the growing period must avoid damage to roots and tubers, and in temperate climates ridges are earthed-up to avoid greening of tubers.

Adoption of drip irrigation and fertigation in potato has proved to be technically feasible and economically viable and beneficial in many ways both in developed and developing regions of the world. Drip irrigation in many diverse agro-ecological situations registered higher yields (40 to 72 tons/ha) apart from saving in water (30 to 40%), fertilizer (20 to 25%) and improving quality of tubers (grade and composition) in comparison to conventional furrow, overhead and centre pivot sprinkler irrigation methods.

Under Turkey and Indian conditions drip irrigated potato registered 50 and 42 tons tubers/ha with an Net Present Value (NPV) of 2085 USD/ha and 2692 USD/ha respectively and a payback period of one year.

For high yields, the seasonal crop water requirements for a 70 to 150-day crop were estimated to be 150 to 750 mm under a range of climatic conditions and varying (70–180 days) length of growing seasons with a daily evapotranspiration rate of 4 to 5 mm/day. Irrigation scheduling using tensiometers enabled an efficient use of water, fertilizer and energy inputs.

Potato is a heavy feeder of nutrients. Its root system is shallow and fibrous, hence fertigation is recommended for higher nutrient availability and use efficiency. The aim of the fertigation program is to cover the difference between crop demand and supply. The nutrient requirements of drip irrigated potato are relatively high. Other best management practices include earthing-up, protection of crop from pests and diseases, need based weed management, harvesting and post harvesting operations to minimize losses.

Potato Best Practices

Best Management Practices (BMPs) are the best recommended agronomic practices for growing a specified crop. These practices are based on research and experience and apply to potatoes under the specified agro-ecological conditions.
The recommended BMPs are not the only way to grow potatoes but are the best way determined by Netafim. The BMPs may change as additional proven research becomes available.

Agro-ecological situation
Climate
Conditions: Temperate, tropical and subtropical; cool season crop; day length: 12 hours
Saturation irradiance: 1200 E/m2/s PAR
Rainfall: 300 to 500 mm/annum
Relative humidity: 60 to 85%
Optimum ambient temperature: 14 to 24 °C

Soil
Soil suitability: Fertile, deep, well drained fine sandy to sandy loams
Optimum soil pH: 5.5 to 6.5
Available P: 35 mg/kg, Exchangeable K: 0.4 cmol/kg, exchangeable Ca: 1 – 2 cmol/kg, Exchangeable Mg: 0.4 cmol/kg
Organic carbon: 1.0 to 1.5
Soil bulk density: 1.3 – 1.4 Mg/m3 favor better root penetration and better tuber development and soil water air relations
Groundwater table: Below 2.0 m
Critical soil salinity level (ECe): 1.7 dS/m above which yield decreases
Soil to avoid: Waterlogged, alkaline and saline soils

Crop rotation
Three-year rotation adequate to check weeds, diseases and pests and avoids yield losses. Without proper rotation yield losses are up to 30% due to soil borne diseases.
The best rotational crops are cereal grains such as wheat and oats, corn, sugarcane, rice and forages.

Varieties
Several varieties with significant differences in size, shape, colour, texture, cooking characteristics and taste are available depending on the country.
Important varieties: Russet burbank, Nicola, Yukon Gold, Desiree.

Planting material
Healthy whole, cut or mini tubers

Spacing
Inter-row spacing: 0.60 to 0.91 m
Intra-row spacing: 0.15 to 0.45 m
Optimum plant density: 75000 to 133000 plants/ha

Seeding rates
Varies with cultivar, market, moisture, planting date, seed size, seed age and cost of production. Generally 1.5 to 3 tons/ha.
Seeding depth 5 to 10 cm.

Land preparation

  • Clod free seedbed with good tilth to express its tuber yield potential, SDI installation and optimal soil water air relations.
  • Destroy the hard pan if any using either chisel plough or a subsoiler.
  • Primary tillage by mould board plough or disc plough and secondary tillage by disc harrows, tyned harrows or rotavator to achieve proper tilth.
  • Broad bed (0.8 m to 1.5 m) and furrow (0.30 m) system.
  • Compost: 25 – 30 tons/ha

Planting for better stand, yield and quality
Poor plant stand registers low yield
Soil temperature at planting 3 – 16°C
Planting depth 5 – 10 cm

Weed control

  • Managing weeds is critical for successful potato production.
  • Weeds compete for light, water, nutrients, etc. and reduce tuber yields by 27% to 73% depending on the weed intensity.
  • Critical crop: Weed competition period is initial 4 – 6 weeks.
  • Integrated weed control program involving crop rotation, manual weeding, good seedbed preparation, soil solarization, maintenance of optimum plant population, mechanical intercultivation and herbicide chemical applications.
  • Recommended pre-mergence herbicides:
    Alachlor: 1.0 – 1.5 kg/ha & Metribuzin: 0.7 kg/ha
  • Recommended post-emergence herbicides:
    Parquat: 0.5 kg/ha & Propanil: 1.0 kg/ha

Irrigation system
Drip version: Surface or subsurface drip irrigation (SDI) combined with fertigation. Fertigation is the application of plant nutrients through an irrigation system, also known as NutrigationTM.

Drip product: DripNet PC, Super typhoon, Dripline 17009
Dripline spacing: 0.9 m for 1 lateral per each crop row and 1.8 m for 1 lateral per two crop rows
Emitter spacing: 0.30 m to 0.40 m
Emitter flow rate: 0.6 LPH, 1.0 LPH, 1.6 LPH and 2.0 LPH depending on soil texture

Crop water requirement & Irrigation scheduling
Estimate crop water requirements as a product of daily reference crop evapotranspiration by Penman-Monteith method and crop coefficient for a given day according to the plant developmental stages.

Begin with 0.5 Kc of daily ETo in the initial period, raise it to 0.8 at vegetative, stolonization and tuber initiation, 1.1 at tuber bulking and it decrease it to 0.7 at harvest period of potatoes.

Daily crop water requirement: 4 to 5 mm/day.
Seasonal crop water requirement: 150 to 700 mm under range of environments.

Irrigation scheduling: 30 cbars using tensiometers installed at 20 cm soil depth maximize tuber growth and grade and yield.

Fertigation
Apply mineral fertilizers based on the targeted yield, leaf analysis results, fertilizer experiment results, leaf deficiency symptoms, nutrient uptake, soil analysis results, and nutrient recycling.

Nutrient uptake:
3 – 4 kg N
1 – 1.5 kg P2O5
4 – 6 kg K2O
0.2 kg CaO per ton of tuber yield
0.3 kg MgO per ton of tuber yield.

Optimum leaf nutrient levels:
10,000 – 15,000 ppm N
0.17 – 0.22% P
7.0 – 8.0% K
0.15 – 0.30% Mg
0.4 – 0.6% Ca
0.15 – 0.20% S
10 – 20 ppm B
2 – 4 ppm Cu
20 – 40 ppm Mn
20 – 50 ppm Fe
10 – 20 ppm Zn

Recommended nutrient dose per hectare:
80 to 120 kg N + 60 to 100 kg P2O5 + 250 to 400 kg K2O

For fertigation use water soluble fertilizers such as:
urea (46% N)
potassium nitrate (13% N & 46% K2O)
monoammonium phosphate (12% N & 61% P2O5)
ammonium nitrate (34% N)

Pests

  • Important pests include Colorado potato beetle, potato tuber moth, leafminor, and cyst nematodes.
  • Important diseases include late blight, bacterial wilt, potato black leg and other viruses.
  • Detect outbreaks and identify problem areas by conducting routine patrols.
  • Monitor economic threshold levels and apply appropriate plant protection measures.

Physiological disorders

  • Internal brown spot: Irregular dry brown spots scattered through the flesh of tubers.
  • Black heart: Breakdown of internal tissues and become black. – Hollow heart: Irregular cavity in the centre of tuber.
  • Chilling injury: Discoloured blotches in the flesh of tubers.
  • Freezing injury:Blue-black discontinuous ring in the vascular region.

Harvesting

  • Maturity and harvest time are influenced by weather, market prospects and the labor situation.
  • Optimum maturity is reached when most of the tubers attain optimum size and the skin is set.
  • To ensure good skin-set, kill the vines using chemicals such as Gramoxone Extra applied at least 3 to 7 days before harvest.
  • Most potatoes are harvested mechanically with potato combines.
  • Harvest during dry periods.
  • Avoid bruising, skinning, or cutting the tubers during harvesting
  • After the harvest potatoes are hauled to the packing shed in bulk trucks, tubers are washed, sized and graded, then placed in bags or cartons for shipment.

Tuber yield
Under drip irrigation and fertigation a good commercial tuber yield is 50 – 60 tons/ha in spring and 35 – 50 tons/ha in autumn depending on length of growing season and variety.
Water utilization efficiency varies between 8 and 12 kg/m3.

FAQ’S

What kind of increased crop production can I expect from converting furrow irrigated potatoes to drip irrigation?

From our field experience in a range of environments it depends on variety used, climatic conditions, length of growing season, management capability, etc. As a rule-of-thumb tuber yields increase by 25 – 40% over traditional furrow irrigation besides 30 to 45% saving in water under timely planting, correct fertigation, weed control and other farming practices.

Why should I opt to irrigate my potatoes by drip?

The drip irrigation of potatoes proved itself to be technically feasible and economically viable over other methods of irrigation under range of environments. Besides increasing tuber yields, drip irrigation prevents tuber cracking and malformation as well as higher gravity of tubers and larger proportion of Grade A tubers. Drip technology also allows significant saving in water, labor and energy required for pumping this resource. It also prevents leaching Nitrogen below the root zone and found to improve fertilizer use efficiency. In the long run, financial analysis shows that drip is the most appropriate system for modern potato growing with higher economic returns.

Why have I got a poor potato plant stand?

A poor potato plant stand can be caused by several factors such as poor quality seed tubers, incorrect planting depths, poor quality irrigation water and incorrect germination irrigation management after planting.

What is potato scab and how can I control it?

Common scab of potatoes is a bacterial disease. Symptoms include tan to dark brown, rough-textured lesions on the tuber surface. Scab is typically introduced into the soil by infected tubers, and will survive indefinitely in the soil. Common scab is most severe in warm, quick-drying soils and increases through a pH range of 5.2 to 8.0. Scab is more of a problem in table potatoes than in processing potatoes, as scab lesions are restricted to the tuber surface and peeling removes the problem. Although scab cannot be eliminated incidence and severity can be reduced through a combination of practices. Among these practices: Avoiding introduction of scab into soil by planting scab-free or treated seed, rotating to other crops for 3-4 years between potato crops, avoiding susceptible crops in the rotation (root crops), green manuring (rye, millet, oat), maintain adequate soil moisture during the time of tuber formation and growth (tuber initiation starts 4-6 weeks after planting), and plant more resistant cultivars.

Should I use subsurface or surface drip system in potatoes?

Subsurface drip irrigation in potatoes raised on broad beds have shown to have many agro- technical advantages. Among them is the flexibility in recollecting the dripline after every harvest cycle using a retrieval machine and protection of driplines from agro-machinery and harvesting machinery damage. Advantages also include the direct application of the water and the fertilizers to the root zone and using the crop agro-machinery without interfering with the day to day irrigation system protocols.

How much does a drip irrigation system cost per hectare of potatoes?

This is very variable and depends on the following three factors:

1. Conveyance of water from source to the filed as this is often the most expensive component of the irrigation system. It depends on the distance and elevation the water has to be conveyed by the pipelines.

2. The amount of water that we need to apply to meet the peak crop evapotranspiration requirements during the crop peak demand. This is a function of prevailing climate conditions, crop canopy cover and efficiency of the irrigation system.

3. Other considerations: The land topography (flat or undulated) of the design area; the soil texture which determines the emitter spacing, for example sandy soils require closer emitter spacing and clayey soil require wider emitter spacing that will have a significant impact on the system cost per unit area.