The Big Decisions: Land, Climate, Soil and Water

Starting a walnut production project is like entering a marathon of never-ending decisions: location, land, soil, water, variety, rootstock, irrigation method, team... Your answers to each of these questions determine your orchard's potential throughout its entire life cycle.

The effects of these first decisions are usually very difficult and costly to change later, and in some cases changing them is simply not possible. These are big decisions that you really must make with great care, and you cannot delegate them to others. You can hire the best technical consultant, but 10 years from now, when your orchard has become a young producing orchard and you see the effects of those initial decisions, that consultant is unlikely to still be around.

So seek as much advice as you can, both from people with a proven track record of success and from those who have failed. But in the end, make sure you reach a level of understanding that allows you to make your own decisions, and take ownership of those decisions in every detail, because you will have to live with their consequences for as long as your orchard exists.

"Every new sailor starts with luck, but only the smart ones gain experience before their luck runs out."
— A popular saying among sailors

Land, Location and Soil

I would almost say that there is no perfect orchard. Even orchards that score highest on most parameters have their challenges, their "Achilles' heels." Choosing the "right" land means navigating between multiple parameters, deciding which to compromise on and to what extent, and taking measures to manage those trade-offs.

To give a general idea, the key agronomic parameters include the following:

• Soil fertility
• Water infiltration capacity
• Workability of the land
• Physical and chemical properties of the soil
• Microclimate
• Chilling hours
• Land availability and price
• Security, electricity and labour availability
• And perhaps most important of all: WATER

There are also non-technical parameters, such as how close the orchard is to your home, a pleasant view, or the expectation that land prices will rise in a particular region. All of these can influence your decisions; but if the real intention is to establish a successful orchard, your "decision-making hierarchy" should give priority to the strategic needs: water availability, soil properties and climate.

Water, Water, Water

Among all of these, water availability is so critical that it deserves to be set apart from the rest. In fact, searching for a walnut orchard site is, to a large extent, searching for a reliable, abundant long-term water source.

Don't listen to anyone who tells you:

• "There is enough water on a given piece of land"
• "And walnut trees don't actually need that much water"
• "Or even if they do, it's only for the first few years"

Comments like these, made without real experience, are often unreliable, biased, or driven by other commercial motives. Instead, get the facts from reliable sources.

Building a Water Budget

Start by making an effort to understand the importance of water, and work towards building a realistic, conservative, long-term water budget that should guide you in planning and diversifying your water sources.

Let's start by stressing this: "A commercially productive walnut orchard" needs a large amount of water throughout its commercial life, increasing every year until it reaches its maximum. It is important to put an objective value on the phrase "a large amount" here.

Your water budget should, at least at the outset, define the flow rates of your sources: wells, irrigation networks, lakes and reservoirs. You must also take the replenishment of these sources into account. In addition, try to build a model of the amount of water you will need in the different years of your plantation.

You should build a mathematical model of the amount of water that can be supplied to your operation (+) and the amount you will use (-). Going a step further, you can also factor in the amount of rain that will fall on the orchard during the irrigation season. However, be very careful: the rainfall received in mm should be assessed using a "discount" factor — in particular, part of short, intense rainfall runs off the surface instead of being absorbed by the soil.

Water Demand at Full Maturity

The safe way to build a water budget is to start by calculating how much water your trees will need once they reach full maturity. To do this, you need to understand the following:

• The mechanism by which water moves within the plant
• How and why plants use water
• How water is lost from the orchard
• The concepts of Evapotranspiration and Crop Coefficient
• Plant moisture stress (PMS) and the effect of relative humidity
• Midday leaf water potential

As a safe, rough figure: plants that reach full maturity need 6,000 - 8,000 m³ of water per hectare per year. Based on an average of 7,000 m³, this equates to roughly 700 mm of water per year for every m² of plantation area.

Water Requirement Model by Year

Year	m³/Ha
1	1.500
2	2.000
3	3.250
4	4.000
5	5.000
6	6.000
7+	7.000 - 8.000

This is an oversimplified presentation of water requirements per hectare by year. Do not make the mistake of using these figures as they are — your actual figures will differ. Make an accurate calculation based on your own climate, soil characteristics and your orchard's canopy each year.

Evaluating the Soil

When evaluating a potential property, you should generally look for good fertility. Among many other parameters, high organic matter is an important indicator of this. You should prefer a chemically balanced soil without excess salt or boron.

Good fertility is often (but not always) associated with soils that have a higher percentage of clay. Clay, the smallest of the three physical particles that make up soil, is often the cause of a major problem: poor drainage.

Two Often-Overlooked Issues

Besides the many features that are popular among those searching for land, two critically important issues are often overlooked:

1. Walnuts Do Not Tolerate Excess Water

Walnut trees do not tolerate excess water in their root zone well. You can manage this to some extent by using certain rootstocks (mostly clonal or hybrid), but in general, soils with a good infiltration rate should be your clear preference.

The shape of the orchard surface is also important for draining water that accumulates after heavy rains. Deeper areas surrounded by higher ground cause water to pond. During land preparation, make an effort to level these surfaces so that excess water drains by gravity out of your planting areas. There will also be other areas where drainage ditches need to be designed and built. A 3D topographic map of your property is a valuable investment you will not regret when identifying the areas that need drainage work.

2. Slope Balance

This may seem to contradict my last sentence, but you should avoid significant changes in elevation across your potential planting area. Just as very flat parcels have their challenges, so do very steep ones. Over the course of the project, you will walk over every square centimetre of the land hundreds, even thousands of times.

On top of the difficulties of moving around the orchard, extreme changes in elevation make it much harder to balance pressure in your irrigation lines. As flat as possible, but with enough gentle slope to prevent water pooling — that is a good balance to aim for when choosing land.