BEST MANAGEMENT PRACTICES
difficult to do if switching soil test methods or laboratories because they often use different methods thus make comparisons difficult . In addition , it is important that the same phosphorus extraction method — the most common are the Sodium Bicarbonate , Bray P1 and Mehlich 3 — is used for consistency in soil test interpretations relative to nutrient concentrations .
In general , soil testing is not extremely helpful for nitrogen and sulfur because the inorganic forms tested for ( nitrate and , in some cases , ammonium for nitrogen and sulfate for sulfur ) are very transient in their soil concentrations as they are regularly changing between plant available and unavailable forms due to rapid plant / microbial chemical transformations . Additionally , the amount of these nutrients released from soil organic matter is very difficult to predict . As such , it is generally best to develop a nitrogen and sulfur management plan based on reliable research studies and previous results and then use soil and plant tissue analysis to fine-tune the recommendations . For example , adjustments to the fertilization plans can be made if unusually high concentrations exist in the soil , plant tissue and / or irrigation water .
The remaining nutrients are managed mostly by soil test values as the starting point . For most of these , a correlation exists between the soil test and probability of a positive plant response — with high likelihood of response at low soil test values with decreasing likelihood of response as soil test values increase . These correlations are relatively good and significant research exists for phosphorus and potassium . However , minimal data is available in turfgrass for the other nutrients , though there are reasonable correlations for calcium , magnesium , zinc , manganese , copper , boron and chloride for other plants ( mostly crops ). These give us some basis for judgment , although the confidence in interpreting results is not as high as with phosphorus and potassium . Nevertheless , there is a slim chance of a positive response to these nutrients if the soil test values are high .
Plant tissue analysis , as discussed below , is an additional tool that can be used to make decisions on these nutrients , but it is rare to see responses in sandy soils with low organic matter . Iron is unique , as the correlations for soil testing are very poor . It can also be difficult to obtain clean tissue samples , as dust is very high in iron concentration . Rather , soil pH and plant species / variety selection are used to help manage for iron .
Soil pH is a measure of hydrogen ion ( H +) activity (“ active acidity ”). The pH scale is 0 to 14 with 7 being neutral . Values below 7 are acidic , and values above 7 are alkaline . Soils tend to range from pH 4 to 8 . The optimal soil pH for nutrient solubility is approximately 6 to 7 . However , turfgrass is commonly grown successfully from pH 5.5 to 8.4 .
Alkaline soil can result in poor solubility of plant nutrients . It is generally not practical or affordable to lower the pH as these systems are highly resistant to change due to carbonates in irrigation water ( hard water ) and in soil ( limestone ). Rather , the nutrient requirement is slightly higher , and managers need to be aware to watch closely for deficiencies of these other nutrients .
Acidic soil also has nutrient solubility issues , as well as toxicities of aluminum and / or manganese . These results are variable by soil , with some worse than others . Acidic soils can be neutralized with limestone ( calcium and / or magnesium carbonate ), burnt lime ( calcium oxide ), hydrated lime ( calcium hydroxide ), or similar , based on a Buffer pH soil test . The quality of the liming materials ( calcium carbonate equivalent and fineness of grind ) also needs to be factored in , as well as ease of handling and cost . Whenever possible , soil pH should be adjusted prior to establishment , as preplant incorporation greatly accelerates the neutralization of the acidity throughout the rootzone . Once turfgrass is established , the ideal time to apply lime is in conjunction with core cultivation , which helps to move the liming material into the soil . Cooler temperatures help to minimize risk of foliar burn . Standard lime applications are usually suitable just about any time of year as long as they do not exceed 50 lbs ./ 1,000 ft ². Extremely acidic soils may require multiple applications over multiple seasons to sufficiently raise the pH . It is best to have a liming program with smaller annual applications to maintain pH at a reasonable level rather than waiting until it drops to a toxic level and then attempting a rescue .
Soil tests may include the following : organic matter , salinity , sodicity , texture , cation exchange capacity and sand size distribution . A soil textural analysis ( percentages of sand , silt and clay ) is important as soil texture can impact water- and nutrient-holding capacity , as well as irrigation , drainage and cultivation . Both texture and sand size distribution are vital for proper construction and maintenance to meet ASTM F-2396 specifications of sand-based rootzones .
Organic matter ( OM ) is not only a source of nitrogen and sulfur , but also all other nutrients . In addition , organic matter increases nutrient and water-holding capacity . Organic matter is often one of the main measures of soil health . Turfgrass is relatively efficient at creating organic matter over time , which is beneficial for the reasons above and as it stores carbon away from the atmosphere . Despite these benefits , organic matter can
14 SportsField Management | February 2023 sportsfieldmanagementonline . com