Vegetable Farming – April 2015

Critical Calcium

Anyone who has spent some time with me is quite aware of the importance I place on available calcium at a critical piece of growing top quality and top yielding crops.  Calcium is key to strong cell wall development and cellular “signalling” (i.e. communication).  The historical influence of William Albrecht and the impact calcium:magnesium ratios play in soil flocculation (i.e. better oxygen availability for microbes on tight or heavy soils) has kept my attention tuned into calcium for the better part of the past decade. On soils which have been historically treated with dolomitic limestone the magnesium levels often go beyond adequate.  True a bit of extra magnesium will help hold some moisture in the soil on light, sandy soils – but I think the drawbacks of excessive magnesium as it relates to nitrogen utilization are worth keeping in mind.

I have been impacted by the work of the late Carey Reams, a controversial agronomist and “healer” – who labeled calcium the “King of Nutrients”.  Reams included an emphasis on calcium(s) in his fertility recommendations – not just a single source/type of calcium – I do know a number of growers who have worked with the Reams targets of available calcium and achieved good results.  Historically Victor Tiedjens may have flown the calcium banner the highest (see his book More Food From Soil Science published in 1965 and available through the Soil & Health Library online, or through current day proponents of his work – Growers Mineral Solutions).  I’m not planning to follow the heavy applications of lime Tiedjens recommended anytime soon, as I would be too concerned with excessive calcium levels tying up other nutrients; I am interested in sourcing different forms of calcium to suit the needs of different soils on our farm, that includes using gypsum (calcium sulfate) on our high magnesium soils, soft rock phosphate on the soils where phosphate and calcium availability are low, and calcitic lime on low calcium soils.  Some growers use aragonite when it’s available at a good price or bone char (another source of calcium and phosphorous); conventional growers have additional tools available to ensure crops have access to calcium through the growing season – most notably calcium nitrate.  We have been using a composted chicken manure from Kreher’s for the past 3 seasons which also supplies calcium (~8-10% Ca) and needs to be considered when determining our complete fertility plan.

My strategy on our farm has always been to supply enough calcium to satisfy crop demands, while maintaining a target pH, and ideally consider how to keep the calcium we apply in the root zone.  Traditional calcitic limestones are a good choice for many situations.  We’ve used Conkline Limestone in Rhode Island as a local source (though their calcium levels are a bit lower than other frequently utilized hi-cal limestone producers in the Northeast – see Lee and Shelburne for the region’s best analysis limestones) and one local grower noted Conklin’s production was on hiatus due to equipment difficulties.  While dolomitic limestone (which contains calcium and magnesium) may still be the most commonly spread lime in these parts, I’ve seen a subtle shift in the recommendations from UMass, in part thanks to the work of John Spargo who spent a brief couple of years at the helm of their Soil & Tissue Lab.

The key to making the Calcium from lime available is all related to the calcium content of the rock, the fineness of the grind (mesh test), and considering the use of additional materials to improve biological activity and to make the calcium in the limestone available.  To this end I can recall hearing Neil Kinsey – an Albrecht follower – impart the importance of adding a humic acid to lime before spreading – and know many folks in other parts of the country are utilizing “carbonized” limestone.  My recommendation, get a current soil test before determining which type of limestone to apply; it costs money when you purchase and apply soil amendments, the investment in soil testing is worthwhile because it will help you determine if you are spending your money in the wisest of ways.

I was excited to see that Wareham Based Solu-Cal (a company affiliated with the local ag supplier Progressive Grower) has received OMRI certification for one of their Solu-Cal products.  I haven’t yet tried Solu Cal yet so will reserve judgement until I experience how their product performs this season.  I think it might be a great option for folks who would prefer to avoid traditional bulk spreading of lime and are looking to boost calcium availability quickly.  It’s more expensive per pound than bulk limestone, but application rates are significantly lower.  Progressive Grower is one of a number of local lime spreaders who offers bulk spreading of either calcitic or dolomitic lime, Progressive Grower also will spread Solu-Cal if that is your preference.  While ordering materials directly from them is your best bet, it’s quite encouraging to learn that Lowe’s, one of the biggest retailers of garden products in our region, is carrying both their enhanced calcitic lime and their enhanced gypsum in their stores under the Lowe’s Sta-Green Lime label – a good option for home gardeners who aren’t in close proximity to Wareham.

For folks interested in the DIY approach, their are recipes for making Water Soluble Calcium from eggshells a la Korean Natural Farming (KNF) methods widely available online and are simple to follow – it won’t replace broader calcium applications on the farm, but it may enhance the natural progression.  We try to take a holistic approach to fertility on our farm; our stewardship of microbes on the farm will play a big role in improving nutrient availability across the spectrum.  Further, anytime we include a focus on calcium on our farm we bring boron into the discussion, as boron is widely considered to influence calcium utilization by crops.  Since the time for reading is well past on the calendar, and it’s solidly the planting season I’ll suggest folks who want to dig deeper archive our bibliography from a 2012 presentation on Calcium, Silica, & Boron at the NOFA/Mass Winter Conference for next winter’s reading season.

Wishing everyone a productive and profitable growing season,

Scroll to Top
Scroll to Top