Applying biosolids with a pH above 7.5 is prohibited to protect Maryland soil health.

Biosolids can be a smart way to recycle nutrients and improve soil structure, but like a good recipe, it only works when the ingredients are just right. One key ingredient in the Maryland nutrient management conversation is the pH level of biosolids before you apply them. If that pH climbs above 7.5, there’s a firm rule in place: application is prohibited. Here’s why that rule exists and what it means for soil health, crops, and the people who work the land.

Let me explain the pH thing in plain terms

Soil pH is a measure of how acidic or alkaline the ground is. Most crops like a near-neutral zone—slightly acidic to mildly alkaline in many cases—because it helps nutrients dissolve so plants can gulp them up through their roots. When biosolids come in with a high pH, they can nudge the soil’s pH up even more. That shift doesn’t just feel like a minor bump; it changes the chemistry of nutrient availability in fundamental ways.

Two big consequences jump out right away:

• Nutrient availability shifts. Some nutrients stay locked away when the soil gets too alkaline. Phosphorus, in particular, can become less available to plants at higher pH levels. Micronutrients such as iron, manganese, zinc, and copper can also become scarce for roots to access, even if the total amounts in the soil aren’t changing much.

• Nutrient balance and uptake can wobble. Plants don’t just need “more” nutrients; they need the right nutrients in the right proportions. When pH strays from the optimal range, roots may preferentially take up certain ions while others lag behind. The end result can look like slow growth, pale leaves, or spots of imbalance that leave crops stressed and less productive.

A closer look at what happens when pH goes past 7.5

When pH crosses that threshold, a cascade begins:

• Phosphorus becomes less available. Phosphorus is essential for energy transfer and root development, but at higher pH levels it tends to bind with calcium and other minerals. The nutrients stay in the soil, but they’re not in forms plants can easily absorb. That means you might see stunted growth or slower root expansion, even if the soil has plenty of total phosphorus.

• Micronutrient availability drops. Elements like iron and manganese are already a tight squeeze in many soils. Push the pH up, and those elements become even more likely to be locked away. The result can be chlorosis (yellowing) and poor photosynthesis, especially in crops that don’t tolerate alkaline soils well.

• Microbial life is stressed. Soil isn’t just a pool of nutrients; it’s a bustling community of microbes that help break down organic matter, release minerals, and build soil structure. Alkaline conditions can slow down microbial activity and shift the community composition. When biology slows, the soil’s natural fertility regs can slip, and the soil can lose some of its resilience.

Why the prohibition exists, beyond the numbers

This isn’t about punishing practices; it’s about safeguarding long-term soil health and crop performance. High pH biosolids can push the land into a less hospitable balance for years. If you keep loading soil with a highly alkaline amendment, you may see:

• A decline in crop uptake efficiency, which means you’re spending more on inputs for diminishing returns.

• A weakened soil microbial ecosystem, making soils more vulnerable to erosion, compaction, and disease pressure.

• Potential interactions with soil minerals that create longer-term imbalances, requiring corrective measures that take time and money to fix.

A practical way to think about it: soil is a living system

Soils are dynamic. They hold water, store nutrients, host tiny life forms, and support plant roots. When one factor—like pH—gets out of balance, the whole system reacts. Think of it like a kitchen with a delicate balance of spices. Add too much of one ingredient, and the dish loses its intended flavor. In soil, the “flavor” is the right mix of nutrients available at the right time, delivered with help from a thriving microbial community. A pH above 7.5 tips that balance unfavorably and makes it harder for crops to get what they need.

What this means in real-life farming and land management

If you’re planning to use biosolids, here are some practical steps to keep things on the right track:

• Test the pH before application. A simple soil test will tell you whether the field is in range for biosolids use. If the biosolids themselves push the field beyond 7.5, plan differently.

• Consider soil pH management first. If a field has a history of high pH, growers often work with lime or other amendments to bring the soil into a more favorable range for the target crop before applying any organic amendments. The goal isn’t just “getting nutrients in” but making sure those nutrients stay accessible to plants.

• Align with regulations and regional guidelines. State and local programs emphasize protecting soil health and nutrient balance. Working within those rules isn’t a burden—it’s a way to ensure soil productivity for years to come.

• Use alternative nutrient sources when pH is a concern. If the soil is elevated in pH, other amendments or nutrient sources that don’t push pH so far alkaline can be better choices for immediate crop needs.

• Plan for the long game. Soil health isn’t a one-season thing. Even a single alkalinity spike can set you back, especially if it coincides with hot, dry weather or crops sensitive to pH shifts.

A few quick tips for staying in the green zone

• Regular soil testing is your best friend. It helps you spot trends early and plan adjustments before issues become costly.

• Keep good records. Track pH, nutrient levels, and any amendments you apply. This isn’t just paperwork—it’s a roadmap for smarter decisions over time.

• Talk to extension agents or soil health specialists. They can translate test results into field-ready actions, like which fields are best suited to biosolids and when to apply to minimize risk.

Common misunderstandings to clear up

• “High pH means nothing if there’s plenty of nutrients.” Not true. Even with high total nutrient levels, plants can’t access what they need if those nutrients aren’t soluble at the soil’s pH. Availability matters as much as total content.

• “If it’s safe for crops, it’s safe for the soil.” Safety is layered. High pH can shift microbial communities and nutrient dynamics in ways that aren’t immediately visible but affect long-term soil health.

• “Only fertilizer pH matters.” Biosolids carry organic matter and microbial life that interact with the soil in complex ways. pH is a big part, but not the only part.

Real-world tangents that still circle back

Biosolids aren’t just about nutrients. They can carry trace metals and organic contaminants if not managed properly, which is another reason soil systems guidelines stress careful pH and handling. It’s a reminder that best practices aren’t about a single number; they’re about an integrated approach to soil health, crop performance, and environmental stewardship.

What we can take away from this

If you’re working with land that might receive biosolids, remember: a pH above 7.5 isn’t a green light. It’s a signal to adjust, test, and plan with care to keep soil biology humming and crops thriving. The rule is a practical safeguard—protecting soil structure, ensuring nutrient availability, and sustaining productive land for years to come.

A closing thought

Soil is a living, patient system. We work with it, not against it. By keeping a careful eye on pH and respecting the boundaries that protect soil health, we help crops grow healthier, soils stay fertile, and farming stay sustainable. It’s a simple idea with big, tangible results—a reminder that the smallest numbers on a test sheet often carry the biggest implications in the field.

If you’re curious, a good next step is to chat with a local extension agent or soil health advisor. They can translate the science into practical steps tailored to your soil type, crop mix, and climate. After all, understanding the why behind the rule makes following it much easier—and a lot more satisfying when you see the long-term payoff in your fields.