A simple study can shed light on the richness and limitations of the soil. This is a key for setting the soil management strategy and fertilization plan.
The first step is looking at the superficial layers of the soil, from the surface until one meter of subsoil. That will show interesting things, such as the petrocalcic horizon which had to be properly managed as explained in a separate post.
I focus now on a 3 hectares field where I have set up an almond orchard in 2015. There is variability in the field, but I could see a brown sandy superficial layer in the first 10 to 15 cm. Bellow that, a progressive accumulation of clay appears which goes deeper than one meter. Those clay rich layers have colours from red to green-blue, depending on the location in the field.
I collected a representative sample of the superficial 15 cm and sent it to the laboratory. There was no major handicap such as salinity or toxicity. Key elements for this soil are pH and carbonates. It is heavily calcareous with strong alkaline reaction, which translates into low availability of micronutrients such as boron, iron, manganese, zinc and copper. In terms of practicalities, high pH cannot be corrected. Calcium is plentiful, which may have an antagonism with Magnesium.
Organic materials are very low. This is something normal in arid lands. It would be desirable to increase this level. However, this is not critical because texture is sandy loam, sodium is very low and soil structure is not bad.
The deep clay layer makes it preferable to use a subsoiler rather than a mouldboard for deep tillage before planting. Since this is dry-farming, the soil management strategy of the orchard consists of using cultivation when necessary to keep the soil free from weeds, especially in spring. Using green manure is advisable every 3 to 4 years, which can be done by letting winter weeds grow and bury them in March.
Macronutrients levels are fine for almond production, which is mainly potassium demanding. No fertilizers are to be provided to the soil, unless further tests show a significant reduction of current levels. The only fertilization plan is a complementary foliar application in September with phosphorus and micronutrients. Even with foliar aplications, high soil pH will translate into micronutrient deficiencies. Effective and cheap means for correcting micronutrient defficiencies exist, as I am to explain in another entry.