How to test soil before fertilizing

How to test soil before fertilizing Practical guide to pre-fertilization soil testing in pistachio orchards Why it matters A proper soil test is the foundation of a sound fertilization plan. It prevents wasted costs, salt build-up, and hidden deficiencies. 1) Best timing - Ideal window: Late winter, before the first heavy fertilizations and seasonal irrigations. - Useful alternative: Right after harvest (to assess salinity and residual nutrients). - Distance from inputs/irrigation: - Sample at least 2–4 weeks after the last fertilization. - Wait 2–3 days after the last irrigation/rain so soil moisture is moderate. 2) Divide the block into management zones - Split the orchard into homogeneous zones by soil texture, slope, cultivar/rootstock, vigor/color (field walk, drone/satellite), and irrigation blocks. - Sample each zone separately; mixing dissimilar areas makes results meaningless. 3) Tools you need - Soil auger/probe or clean stainless-steel spade; clean plastic bucket; heavy zip bags or sample jars; disposable gloves; waterproof marker; labels; GPS/app to log locations. - Note: Avoid galvanized/brass tools when testing micronutrients (risk of Zn/Cu contamination). 4) Depths and number of samples (pistachio-specific) - Depths: 0–30, 30–60, 60–90 cm. For deep rooting or detailed salinity checks, include 90–120 cm. - Number of cores per zone and depth: 10–15 (ideally 15–20) zigzag/random points, then composite. - Position vs. irrigation: - Drip/microjet: sample within the wetted bulb. For salinity monitoring, also take a set from the edge of the wetted bulb (salt accumulation zone). - Flood/furrow–ridge: zigzag across in-row and inter-row; build one composite per depth. - Young trees: 0–30 cm (and 30–60 cm if roots have reached it) is often sufficient. 5) Step-by-step sampling - Remove surface debris (leaves/mulch). - Drive the probe vertically; keep each depth layer separate in a clean bucket. - Repeat across the zone in a zigzag until you have 10–15 cores. - Combine: thoroughly mix soil for each depth in a clean bucket, break clods; remove stones/roots. - Subsample: use quartering to retain ~0.5–1.0 kg per depth. - Label completely: orchard/zone name, irrigation type, depth, date, last irrigation/rain, last fertilization, sampler’s name, coordinates/GPS. 6) Storage and shipping - Keep samples cool and shaded; deliver to the lab within 24–48 hours. - If immediate shipping isn’t possible: air-dry a thin layer in shade (do not oven/heat). For nitrate testing, keep a subsample cold (refrigerated/frozen) to prevent change. - Coordinate with your lab; some prefer moist soil for salinity (ECe) measurements. 7) Which analyses to request (suited to calcareous/semi-saline soils) - General chemistry and salinity: - pH and ECe (saturated paste), soluble ions (Na, Ca, Mg, K, Cl-, SO4^2-, HCO3-), exchangeable sodium/ESP and, if possible, SAR of the saturated paste extract. - Calcium carbonate equivalent (free lime), organic matter, cation exchange capacity (CEC), texture. - Macronutrients: - Mineral N (NO3-N and NH4-N), plant-available P (Olsen-P for calcareous soils), exchangeable K (ammonium acetate extract), exchangeable Ca/Mg, sulfate-S. - Micronutrients: - DTPA-extractable Fe, Zn, Mn, Cu; hot-water–soluble boron (B). - Optional but useful: - Chloride and boron in the saturated paste extract (toxicity risk), gypsum requirement if sodicity is suspected. - Complementary: Test irrigation water at the same time (EC, pH, cations/anions, SAR, boron/chloride) to understand water–soil interactions. 8) Frequency and scheduling - Full panel: every 2–3 years per management zone. - Simple annual check: pre-season for ECe/chloride/nitrate and P, K in 0–30 and 30–60 cm. - Leaf analysis as a complement: mid-summer from mid-shoot leaves on non-fruiting shoots to fine-tune fertilization. 9) Common mistakes that spoil results - Sampling right after fertilizing or with too few cores. - Mixing depths into a single bag. - Sampling atypical spots (next to manure piles, unusual shade, storage areas). - Using dirty/galvanized buckets/tools (Zn/Cu contamination). - Incomplete labels or sample mix-ups. - Ignoring the salt “ring” at the wetted-bulb edge under drip irrigation.