As spray tanks pack in more active ingredients and liquid fertilizers, incompatibilities spike — from precipitates to gels. A growing toolkit of compatibility agents, water conditioners, and chelating chemistries is turning those complex cocktails into uniform, effective sprays.
Industry: Agriculture | Process: Fertilizer_Application
Modern crop spray tanks often combine multiple active ingredients (AIs, the pesticidal components) and liquid fertilizers to save time and fight resistance — and that complexity is driving more compatibility problems. Mixing hydrophobic (water‑repelling) herbicides with high‑ionic‑strength fertilizer solutions can trigger precipitates, gels, or phase separation (news.agropages.com) (news.agropages.com).
One industry analysis notes over 75% of commercial compatibility agents are phosphate‑ester surfactants, often nonylphenol ethoxylates (news.agropages.com). Reflecting how ubiquitous they’ve become, the global agricultural adjuvant market — which spans surfactants, buffers, emulsifiers and more — was ≈$2.9 billion in 2018 and is projected to exceed $6.5 billion by 2032 (≈5.6% CAGR) (fortunebusinessinsights.com). Activator adjuvants (surfactants and related additives) are projected to comprise ~78% of this market by 2025 (fortunebusinessinsights.com), largely driven by herbicide use. Cost matters too: adding adjuvants (~$0.75–1 per acre) has been reported to improve spray absorption by 50–85% (fortunebusinessinsights.com).
Activator and compatibility adjuvants
Surfactants and activators (surface‑tension‑lowering additives that improve wetting and spreading) underpin many herbicide programs — market data show activator adjuvants dominate usage, especially with herbicides (fortunebusinessinsights.com) (fortunebusinessinsights.com). By boosting leaf coverage and penetration, they contribute to the reported 50–85% uptake gains (fortunebusinessinsights.com).
Compatibility (mixing) agents are designed specifically to keep all tank components in one phase. Many are phosphate‑ester derivatives formulated to “disperse and stabilize tank mix partners” for a homogeneous spray solution (syensqo.com). In practice, they can prevent flocculation or gelling when oil‑based pesticides, dry powders, and liquid fertilizers share a tank. Yet standard compatibilizers can still fail in very complex mixes; industry reports point to newer formulations — varying ethoxylation or hydrophobe length — to tackle tougher cases (news.agropages.com) (news.agropages.com).
Wetting/spreading agents (surfactant‑type adjuvants) improve deposition on waxy or hairy leaf surfaces, often spreading droplets uniformly and sometimes doubling spray coverage on difficult foliage.
Water conditioners and hardness antagonism
Hard water rich in Ca2+, Mg2+, or Fe2/3+ can deactivate pesticides by precipitating them. Glyphosate efficacy, for example, drops when Ca2+ forms insoluble glyphosate salts (cdnsciencepub.com). Water‑conditioning adjuvants address this by sequestering cations. A common tactic is ammonium sulfate (AMS): at ~2–3 L/ha, sulfate ties up Ca2+ as CaSO4, freeing glyphosate to bind NH4+ and remain soluble (cdnsciencepub.com). In trials with glufosinate under very hard water (>1799 ppm Ca/Mg), AMS raised weed control and yields by ~11% versus no AMS (cdnsciencepub.com).
Chelating or acidifying agents can also lower pH and “grab” metal ions; supplier guidance notes hard‑water minerals “can deactivate the pesticide by complexing the active ingredient into precipitated salts,” and that water‑conditioners as tank‑adjuvants “sequester minerals” (syensqo.com). In operations that pretreat make‑up water, a softener (ion‑exchange for hardness removal) can be part of that upstream strategy; see softener.
Chelating agents and micronutrient availability
Chelating agents such as EDTA, DTPA, and EDDHA (ligands that bind metal cations with multiple donor atoms) keep micronutrients like Fe, Zn, Cu, and Mn soluble by preventing reactions with hydroxide (OH–) or phosphate (PO43–) that form insoluble precipitates. Iron is a classic case: unchelated Fe2+ oxidizes to Fe3+ and drops out as brown ferric hydroxide, whereas chelated Fe formulations “stabilize iron ions and protect [them] from … precipitation,” improving availability (cropnuts.helpscoutdocs.com) (spring-lake.net).
Chelate choice is pH‑dependent. At pH 7.5, nearly 100% of Fe‑EDDHA remains chelated, versus ~50% for Fe‑DTPA and just 2.5% for Fe‑EDTA (spring-lake.net); crop trials similarly show Fe‑EDDHA >> Fe‑DTPA >> Fe‑EDTA in correcting iron chlorosis at high pH (spring-lake.net). Industry tables list effective pH ranges: EDTA ~1.5–6.5, DTPA ~1.5–7.5, EDDHA ~3–11 (cropnuts.helpscoutdocs.com). In alkaline tank mixes, EDDHA‑type chelators therefore keep Fe and other metals in solution longer, preventing “lock‑up.”
Compatibility gains extend to pesticide–fertilizer blends. In one Syngenta patent, tank‑mixing crop‑protection emulsions with liquid fertilizer only stayed stable when 3% EDTA (or EDDHA‑style chelates) was included; the chelator prevented the sedimentation and flocculation observed without it (patents.google.com). Mechanistically, the chelator binds cations in the fertilizer — e.g., Ca2+ or trace metals — before they can precipitate actives. Many micronutrient fertilizers already contain built‑in chelates for this reason.
Jar testing and mixing sequence
Despite planning, incompatibilities still surface. A small‑scale jar test is the first diagnostic: in a clear jar, fill half with the actual carrier (the same water or liquid fertilizer to be used), add products at intended concentrations in the exact order they would enter the tank, cap, agitate, and observe (edis.ifas.ufl.edu) (edis.ifas.ufl.edu). Clumping, rapid settling, layering, or excessive foam usually appear within 15–30 minutes; a stable mix remains uniform (edis.ifas.ufl.edu). Jar tests primarily detect physical incompatibilities; label‑mandated PPE and safety steps still apply.
Mixing sequence matters. The commonly cited A.P.P.L.E.S. order is: (A) conditioning agents first (e.g., ammonium sulfate, acidifiers), (P) water‑soluble powders, (P) powder dry forms (wettable powders, dry flowables), (L) liquid flowables (SCs and similar), (E) emulsifiable concentrates (oil‑based ECs), (S) solutions (SL), with remaining surfactants/oils last — ensuring each step fully disperses before the next (edis.ifas.ufl.edu) (edis.ifas.ufl.edu) (edis.ifas.ufl.edu). Starting with conditioners (AMS, citric acid, antifoam, etc.) gives time to neutralize hardness ions or foam before other actives are added.
Field fixes with chemical additives
If jar tests reveal problems, compatibility agents can re‑stabilize gelling or separating mixes; phosphate‑ester adjuvants are routinely used to re‑emulsify stubborn components (news.agropages.com). Accurate metering supports consistent results when conditioners or adjuvants are used; growers often specify an in‑line dosing pump for precise chemical dosing.
Water hardness can antagonize cation‑sensitive herbicides. Evidence shows adding AMS at about 2.5 L/ha binds Ca2+ (forming CaSO4) and frees glyphosate to bind NH4+, improving uptake (cdnsciencepub.com), with one glufosinate trial reporting an ~11% yield increase under very hard water (>1799 ppm Ca/Mg) when AMS was included (cdnsciencepub.com). Alternatively, liquid acidifiers or chelating conditioners (e.g., EDTA salts) can pre‑bind hardness ions and/or lower pH; many tank‑mix adjuvants combine acid buffers and chelators because hard‑water ions “can deactivate” pesticides unless sequestered (syensqo.com).
pH buffers are another lever. Some actives (e.g., glyphosate or certain fungicides) are pH‑sensitive; lowering an alkaline mix’s pH can re‑dissolve some precipitates. Operators report that slowly adding vinegar or citric acid while stirring can clear an alkaline‑induced precipitate; conversely, if acidity is creating surface films or corrosion risks, a carbonate or buffer addition may be warranted. Labels frequently specify a pH 4–6 target for glyphosate stability.
Foam management supports sprayability. Excessive foaming from agitated surfactants can overflow tanks; silicone antifoams are commonly used. If dry powders clump or oil phases separate, adding a nonionic surfactant, emulsifier, or crop oil concentrate can improve emulsification and wettability. After any complex application, thorough sprayer cleanout helps prevent residue carryover; even with additives, vigorous agitation during spraying keeps mixtures uniform. In practice, “clean, then re‑test” applies when trying any new combination (edis.ifas.ufl.edu) (edis.ifas.ufl.edu).
Operational guidance and sources
Labels and compatibility charts are the final word; some mixes are prohibited outright. If guidance is absent, the combination of a jar test and manufacturer tech bulletins or mixing‑support tools (e.g., MixTank apps) is standard practice. Extension programs detail these steps — see IFAS mixing guides for jar tests and sequencing (edis.ifas.ufl.edu) (edis.ifas.ufl.edu) — while ag‑chem formulators document compatibilizer performance and formulation trends (news.agropages.com) (news.agropages.com). Market analyses quantify adoption and benefits (fortunebusinessinsights.com) (fortunebusinessinsights.com) (fortunebusinessinsights.com) (fortunebusinessinsights.com), and peer‑reviewed studies illustrate outcomes for hard‑water antagonism and AMS efficacy (cdnsciencepub.com) (cdnsciencepub.com) (cdnsciencepub.com). For micronutrients, supplier guidance and reviews cover chelate stability and pH windows (cropnuts.helpscoutdocs.com) (cropnuts.helpscoutdocs.com) (spring-lake.net) (spring-lake.net) (spring-lake.net), and patents demonstrate how chelators prevent fertilizer‑pesticide sedimentation in practice (patents.google.com). When water conditioners are required, supplier notes emphasize “sequestering minerals” to avoid pesticide deactivation (syensqo.com).
