Jatropha as an irrigated crop.
One of the first Jatropha projects with irrigation was started in Egypt, not far from Luxor. It is part of a very large forestation scheme. The Jatropha part is often referred to as a D1 project, which is not the case although it appears that one of the (many) former directors of D1 (David Sonnenberg) used to be involved in the project.
Precipitation in Luxor and temperature in Luxor
In this climate no cultivated plant will survive. No rain, very hot during daytime, cold at night. So this is the ideal climate to experiment with inputs.
Consider it a greenhouse without a roof and a given temperature. Irrigation will make the difference here. Since there is practically no rain, you are in control. You can supply water when and how much you want. On top of that the water can be the carrier of nutrients.
This picture ( unknown photographer) of the reforestation site in Luxor including Jatropha was one of the first Jatropha pictures on the internet, copied by everybody, including me. These plants are completely depending on irrigation water from sewage. This is what they receive: (drip irrigation with recycled sewage water.)
10 litres every 20 days in winter. 20 litres every 10 days in summer
Calculated on a 50/50 base, these plants get 456 litre/plant/year. This means, based on a density of 3x3 (1111/ha) 506616 litre per ha, which is 50.6 litre per m2, which is 50,6 mm/m2. This seems very little, but since drip irrigation usually gives you an efficiency of at least 90% over rain or surface irrigation, the 50.6 mm/m2 should be compared with roughly 500 mm rain, which is the absolute minimum to grow Jatropha.
In Israel an interesting irrigation experiment is going on with different levels of irrigation . Although the trial only started in late 2008, it is already significant that the highest level of irrigation gives the best results. (Both in growth and flowering) (verbal information 2009, although no water amount was mentioned)
In Singapore JOIL is experimenting with intermittent drip irrigation. Only when the plant is in a stage where water is indispensable (e.g.newly established plantings) and the climate is not providing it, the system will supply water at an average quantity of 5 liter per plant per week.
The pictures below show various irrigation systems in various countries. Note: irrigation is expensive and can be troublesome. Jatropha needs water but does not like wet feet. (See diseases)
If the crop is irrigated, it makes sense to combine irrigation with fertilization.
Apart from drip irrigation, Jatropha is also grown with furrow irrigation, flood irrigation and mini sprinklers. The quantities of water used differentiate substantially.
Dormancy and irrigation.
Dormancy of Jatropha can heave different causes.
1. The temperature becomes to low(below15-18 C) Jatropha stops growing and starts shedding leaves. In this type of climate irrigation should be stopped as well, because it will do more harm than good.
2. Temperature remains tropical, but by the lack of rain Jatropha sheds the leaves and goes into dormancy. This dormancy can be broken trough irrigation, allowing the plants to make a second flush. From flower initiation to ripe fruits takes about 85-90 days, so two harvests should be possible.
3. Continuous irrigation in a tropical climate. The plant will grow all year. Depending on the nutrient balance it will either grow or flower. High P soluble nutrients will influence flowering positively.
4. Continuous irrigation can produce problems as well. In a project in Senegal (Durabilis) continuous irrigation caused serious problems with Fusarium wilt.
A trial with a planting density of 2x2 (2500 plants/ha) was irrigated with 18 litre per day/plant which equals 4.5 mm/m2/day. In relation to the climate in the trial area, a continuous irrigation scheme would probably run from March till October, this means 4.5 x 300 (days) = 1350 mm/m2/year. Although this is not extreme compared with tropical rain fed area's receiving +2000mm, the plants in the trial could not cope with it, mainly because the rooting area was constantly wet.
Interpretation of climatological data and statistical data in general.
These graphs from www.sunmap.eu clearly show what happens if one bases conclusions on average rainfall and temperature. According to the left figure, the climate is perfect for Jatropha and with some additional irrigation the plant would grow all year. On the left graph one can see that there is an absolute dormancy period due to low night temperature between November and February, where irrigation would do more harm than good.