Soil Tillage is not prohibited by organic standards. Each crop system has its own unique needs and management practices for soil building. But in our case, a no-till system really makes sense (if you ignore what the gophers do!). Summer irrigation produces a lot of grass and wood-decay fungus. By September, we allow the soil to dry substantially, and the grass stops growing (mostly). We use a flail type mower to cut very short and prepare the orchard floor for harvest. You can really see the difference between our orchards and most walnut orchards just by looking at the ground beneath the trees.
Compost, manure, and wood chips feed the fungus. Mycelial mass increases, adding to long-term soil organic carbon. This, and many more unseen processes improve soil health. The results are dramatic, even if they can't be easily measured. Long term benefits include improved moisture holding capacity, a higher rate of water infiltration, more water stable aggregates, greater biodiversity, carbon sequestration, and better nutrient cycling.
Irrigation is supplied by ground water. Sometimes we have a lot, sometimes not so much. The water table in this small valley responds very sensitively to winter rain. By the end of December, a 'normal winter' rainy season will start the creeks flowing which quickly raises the water table. The deep soil (8 feet or more) retains a great deal of water well into the summer. That alone supplies the trees with 80% of their needs. We add about 6 additional inches of water to keep them comfortable in the hottest months of July and August.
Hull split occurs naturally in October. Most "conventionally" grown walnuts are sprayed with a chemical that interrupts ripening, causing hulls to split before the nut is fully mature, and allows for early harvest. Allowing our nuts to full riper and reach maturity naturally improves their flavor substantially.