Forage & Grains
Addressing Low Soil Calcium Improves
Forage Quality & Economic Return
By Cindy Dailey, California State University, Chico, College of Agriculture, Organic Dairy Program
Added December 9, 2012. The success of any organic farming system can be linked directly to soil fertility. High quality forages that optimize milk production require well-aerated, balanced soils. Getting “there” takes commitment and in some cases, blind faith that investing in your soils can actually provide a generous return, a return that continues to pay dividends long after the deposit is made into the proverbial soil bank account.
Making that initial investment was an important step in the organic evolution of the certified acreage at the University Farm. The investment was considered a pledge to the concept that soil remediation would return value to the operation in some tangible way. With the help and advise of the Organic Dairy Advisory Board and Agri-Dynamics (our consulting partner on the study), a long-term soil remediation field trial was designed to study the effect of a basic soil amendment program on forage quality and yield, with an emphasis on the economic return that would result from added milk production.
Soils in this area are classified as “Chico Clay Loam”, with a pH of 6.6 and CEC of 13.8. The initial soil analysis would show significant deficiencies in base saturation for calcium (55%), excessive amounts of magnesium (33.8%) and elevated phosphorus (23 ppm), moreover both soil nitrogen and sulfur concentrations were far below recommended norms. Such a significant deficiency in soil calcium (Ca) would likely compromise nutrient uptake in pasture forages, reducing digestibility and consumption.
Although the initial soil organic matter (SOM) assessment was within the normal range (3.5%), soil penetrometer readings were very high (greater than 75% of readings in excess of 300 psi), indicating “tight” soils in need of aeration and soil biology. Soil Ca has a positive impact on soil structure by flocculating clays (breaking them up into flakes), in this way, Ca content works to improve water movement and aeration within the soil profile. The low base saturation for Ca may help to explain (at least in part) the compaction issues in these soils.
Methods: Ten 5-acre paddocks were randomized to one of two treatments, i.e., amended vs. non-amended, for the purposes of monitoring changes in forage quality and yield over time in response to a calcium-based remediation program. Amended paddocks received a combination of soil amendments designed to remediate the soil over a three-year period to defray these initial costs. All amendments were applied in the fall, with the exception of the spring gypsum application. Amendments for the treated paddocks included:
Amendments were applied each year for three years at a cost of $289.50/yr. Pastures were all managed the same with respect to intensive grazing management or MIG with a stocking density that varied throughout the season (100 -130 cows/acre). Rest periods also varied with season, for instance during the spring of the year, paddocks were rested 25-30 d, as the summer progressed, the rest periods would take 45 days to achieve 10-12 inches of re-growth that was suitable for grazing. During spring, our pasture DMI can easily reach 70% of DMD, while changes in forage quality during the heat of the summer can reduce pasture forage consumption to approximately 40%. Summer heat changes the plant populations from cool to warm season species, elevating ADF and NDF, therefore reducing forage intake. As NDF rises, pasture DMI drops because feed takes longer to break down within the rumen, rate of passage slows, and the cow becomes limited on space (capacity).
All paddocks were measured for dry matter yield pre and post grazing using a Grass Master brand capacitance probe. Total dry matter removed was calculated by subtracting post DM values from pre-grazed DM readings. The difference was considered to be DM yield, as well as actual dry matter consumed. Residual DM measured approximately 1500 lbs/acre, pre-grazing DM production varied by season. Total average DM production per year averaged 6 T/acre.
Results: The results for forage quality and yield are averaged over for the last three years. It was not possible to pick up differences between treatments visually even though changes in forage quality and quantity did occur.
Dry matter production data indicated an additional 180 lbs of dry matter/grazing cycle within the amended paddocks. With 8 grazing cycles / grazing season the additional tonnage/acre was 1,440 lbs of DM/acre. Cost of forage production in our irrigated system is roughly $0.08/DM lb, returning an additional $115.20 per acre per year in the amended paddocks.
If we were to calculate the cost of replacing that 1440 lbs of DM with comparable feed, it would cost approximately $253/acre to buy $300 hay at 85% DM. For the 50 acres within this study, that amounts to roughly $12,600 worth of hay that we didn’t have to buy because we were able to increase our production of pasture-based forages.
What is more exciting than yield is the change observed in overall quality. Obviously, as forage quality increases/lb of DM consumed, so will milk production. There is a direct correlation between forage quality and milk yield.
Acid Detergent Fiber or ADF was significantly improved (34.45% A vs. 36.67% NA) indicating a reduction in the fiber content of the forages. Neutral Detergent Fiber or NDF was also significantly improved within the amended paddocks (52.02% A vs. 58.10% NA), to the benefit of pasture intake because of the inverse correlation between NDF and DMI. What’s more, the overall digestibilty of the fiber content of the feed improved within the amended paddocks as reflected in NDFD or neutral detergent fiber digestibility. As the fiber content of the feed becomes more digestible, more total nutrients are then available to the cow for milk production and maintenance. In fact, for each 1% improvement in NDFD, DMI or dry matter intake improves by 0.37lbs, resulting in an increase in fat corrected milk production of 0.55 lbs/lb of dry matter consumed.
The energy content of the forage also improved significantly within the amended paddocks (across all energy categories), improving relative forage quality (RFQ) within the amended paddocks by 20% (189.85 A vs. NA158.69). Improvements in the overall digestibility, total digestible nutrients and the energy component of the forages within the amended paddocks resulted in more milk production produced per ton of DM consumed (3,298 for the A treatment vs. 2,966 for the NA treatment).
Economic impact: Using the milk production lbs/ton of DM statistics, cows grazing the amended paddocks produce an additional 331.7 lbs of milk for every ton of DM consumed. In our grazing system, each cow consumes over 2 T of DM from pasture-based forages over the course of the grazing season. (e.g., @40 lbs of DMD and 50% pasture DMI; grazing 200 days = 2T/cow/season).
Cows that consume 2T of amended forages throughout the season, will produce an additional 662 lbs of milk over cows grazing on non-amended paddocks (2 * 331 lbs of milk/T DM consumed = 662 total additional lbs of milk produced), at $28/CWT = $185.36 per cow. For our 90 cow herd, that would be $16,682.40 for the year due to improved forage quality.
The additional yield was calculated to be $5,760 for the season due to the soil amendment program. Collectively, the treatment yielded $22,442.40 in additional income.
The amendments themselves (with application expenses) cost $289.12/acre, for a total investment of $14,457 for the 50 acres allocated to the dairy unit. Net return = $7,985.40 for the season. The actual return on investment suggests that for every dollar invested in soil (under the conditions set by this study), there was a $1.55 returned in additional income.
The caveat is that this study was conducted on low calcium, high magnesium soils, under irrigation, and MIG grazing with primarily Jersey-cross cows. Results on your farm would depend on your current soil fertility and cost of remediation, which are all site-specific but no less applicable. You won’t know until you test your soil and run some numbers to establish costs. If your forage quality and yield are not yet there, you may need to test and get started, sooner rather than later.
There are a number of things that we did not factor into the economic picture including the reduction in grain costs. As energy values in the forages improve, the need for energy from grain will be reduced, something that would have a significant impact on feed costs and net profit/cow.
In addition, we did not calculate the economic impact of improved soil organic matter (SOM) that comes from a more balanced soil. Higher SOM values would enhance the water holding capacity of the soil, reducing irrigation costs over time.
In summary, achieving balanced soils is essential to improving net profit in a pasture-based organic dairy system predicated on high forage intake and optimal milk production levels. To get to that next level in your program, test your soil & your forage, find a good agronomist or soil coach that can help you understand the data, establish some achievable goals and pull the trigger.
Acknowledgements: We would like to thank and acknowledge Organic Valley Family of Farms for their support of this research through the Farmers Advocating for Organics (FAFO ) fund. We would also like to thank Agri Dynamics for serving as the technical consultant and industry advisor for this study. With their help, we were able to create a study that was relevant and applicable to the needs of the organic dairy industry. Your service and expertise has been greatly appreciated by our staff and students.