According to recent United Nations estimates, the world’s population is projected to grow to nearly 10 billion by 2050, which will require boosting agricultural demand by an estimated 50% to meet this global food challenge1. To support this need, farmers worldwide must increase crop production by enhancing productivity on existing agricultural land through innovative methods like precision farming and plant nutrition management. Proper plant health maintenance, such as soil and foliar applications of micronutrients and fertilizers, is crucial to optimize nutrient uptake and support growing crop yield.
Micronutrients are essential for plant growth and play an important role in balanced crop nutrition. Commonly composed of minerals like iron, zinc, manganese, boron and copper, micronutrient solutions can be applied in soil or by foliar application as soluble metal salts, insoluble metal carbonate or metal oxides. Organic carriers such as ethylenediaminetetraacetic acid (ETDA), amino acid, humic acid and kraft lignosulfonates (kraft lignin) play a prominent role in the dissolution of micronutrients and their transport to plant roots.
Specialty chemical producer Ingevity is the world’s largest producer of kraft lignin, and as such offers an array of high-quality, sustainable lignosulfonates. These bio-based lignosulfonates protect micronutrients from oxidization or precipitation, remediate leaf burn, and extend the absorption time on the crop. With a low molecular weight, kraft lignin contributes to low viscosity formulations without threatening the environment.
The multifunctional value of kraft lignin for micronutrient applications
Ingevity's bio-derived kraft lignin aids as a micronutrient complexing agent for water-soluble metal ions due to its unique 3-D structure, suitable molecular weight and multifunctional moiety-metal interaction capabilities. Compared to the commonly used chelating agent EDTA, kraft lignin’s multi-level complexation structure adapts to a wider pH range, allowing application compatibility with various soil properties. Its weaker complexation strength offers easier release of metals into soils and plant leaves. Also, the hydrophilic sulfonate groups make kraft lignin a natural humectant, ensuring prolonged absorption time of the agricultural chemical. Lastly, when formulated with insoluble metal oxides, Ingevity’s kraft lignin can serve as an excellent dispersant by providing impressive surface coverage and steric stabilization. Table 1 includes Ingevity’s most frequently used products in micronutrition applications.
Table 1. Ingevity kraft lignin products designed for micronutrient applications.
1. Nikos Alexandratos and Jelle Bruinsma, “World Agriculture Towards 2030/2050: the 2012 Revision,” Food and Agriculture Organization of the United Nations, June 2012, http://www.fao.org/3/ap106e/ap106e.pdf.
Crop friendliness without sacrificing performance
Kraft lignin’s inherent functionalities (phenolic hydroxyl, carboxylate) form much weaker complexation with metal ions when compared to those from EDTA. Figure 1 below compares the complexation stability constants (Log K, where K is the equilibrium constant) of several model phenolic compounds and aromatic carboxylic acids with different divalent cations, using EDTA as a reference. The weaker complexation stability is advantageous for ions to be released from the complex and absorbed by the plant rooting or foliar system. In turn, the regenerated lignosulfonates can complex with the remaining micronutrients.
Figure 1. Complexation stability constants (Log K) of model phenolic and aromatic carboxylic acid compounds with divalent cations compared to EDTA.
As a natural humectant, kraft lignin provides improved wetting and prolonged foliar absorption. As shown in Figure 2, zinc-kraft lignin (ZnSO4-KLS) complexes can absorb 8% moisture, while zinc sulfate (ZnSO4) only absorbs 1%. Formulations with kraft lignin dry more slowly than sulfate solutions and EDTA complexes, allowing longer uptake time for foliar applications. A naturally derived product, kraft lignin does not cause phytotoxicity, remediating leaf burn if nutrient overdose occurs.
Figure 2. Moisture uptake study of ZnSO4 and ZnSO4-KLS complex.
Demonstrated plant health and crop height in the field
Ingevity collaborated with The University of Florida on a tomato greenhouse study of kraft lignin-based micronutrient products (Table 1) to determine the efficiency plant health and crop yield. A blend of various uncomplexed inorganics, including sodium borate (Na2B4O7); copper sulfate (CuSO4); iron sulfate (FeSO4); magnesium sulfate (MnSO4); sodium molybdate (NaMoO4); and ZnSO4, was used as the control group to compare to a blank study group excluding inorganics. In the experimental groups, one inorganic salt was replaced by the kraft lignin complexed product and applied to soil types with pH levels of 6.0 and 7.5. Crop height was measured after 16 days of the application, and plant yield was represented by fresh weight and dry weight provided in Table 2. All lignin-based experiment groups demonstrated increased crop height and plant yield. For example, more than a 20% crop height and yield increase was observed when using complexed zinc or magnesium.
Table 2. University of Florida tomato greenhouse study of Ingevity’s kraft lignin micronutrient formulations.
Ingevity also conducted additional third-party field trials for rice, sorghum, soybean and carrots among different soil conditions (Table 3). The application of zinc complexes with Ingevity’s kraft lignin corrected chlorosis and increased the yield by 61% for rice and 37% for sorghum. For soybeans tested on a nearly drained and metal-deficient soil, 12% crop yield was observed with a 60% lower application rate of the KLS-metal complexes. Following the foliar application of complexed magnesium, carrots showed complete greening of leaves within one week of application and a 30% yield increase.
Table 3. Third-party field trials of Ingevity’s kraft lignin micronutrient formulations.
Easier formulation and reduced costs
Since lignosulfonate-based micronutrient products are typically delivered in liquid form, the formulation viscosity and stability are key considerations in the process of production, storage and field application. Common undesirable formulation performances include high product viscosity and formation of precipitates. With high-solid loading, low viscosity and long-term solution stability, Ingevity’s kraft lignin products provide farmers with formulation flexibility, reduced shipping cost and improved user friendliness.
Ingevity’s Reax® 100M is specifically designed for micronutrients complexation, offering a high degree of functionality for optimal metal complexation and aqueous solubility, and a low molecular weight decreasing solution viscosity. For example, a solution with 40% Reax 100M can be easily prepared by simple mixing to achieve a readily flowable solution viscosity of approximately 30 centipoises. A nearly saturated ZnSO4 solution with 15% of zinc and a MnSO4 solution with 12% of magnesium were prepared in deionized water. Stable KLS-metal complexation solutions can be prepared from any given ratio between the 40% Reax 100M solution and the metal solutions, indicating formulation flexibility with the use of a wide range of concentrations.
For illustration, solutions with a weight ratio of 1:2 between Reax 100M solution and the metal solutions are demonstrated in Figure 3 below. A sulfite lignin product with 30% solid is also used for the comparison study. Solutions prepared with Reax 100M exhibit impressive stability with no precipitations. Solutions containing sulfite lignin were initially cloudy after blending and separation was observed after three days.
Figure 3. Photo of lignosulfonate metal complexation solutions as observed after three days. Solution A: 7 grams (g) of Reax 100M solution (40% solid) and 14 g of ZnSO4 solution (15% element Zn); Solution B: 7 g of Reax 100M solution and 14 g of MnSO4 solution (12% element Mn); Solution C: 7 g of sulfite lignin solution (30% solid) and 14 g of ZnSO4 solution; Solution D: 7 g of sulfite lignin solution and 14 g of MnSO4 solution.
Metal oxides or carbonates, such as copper oxide (Cu2O) and manganese carbonate (MnCO3), are insoluble, meaning the settling of these particles over time will negatively impact the formulation’s application efficiency. Ingevity’s kraft lignin products have proven valuable in dispersing insoluble metals and challenging pesticides due to their steric stabilization abilities. A formula was created with the ratio given in Table 4, and the average particle size in the suspension was 3-4 micrometers (μm). Figure 4 below shows no precipitation from the suspension after testing the formulation at 45℃ for one week. Even after nine weeks of storage at 45 ℃, the formulation has minimal particle growth and good suspensibility.
Table 4. Aqueous suspension of metal oxides and metal carbonates with Ingevity’s kraft lignin products.
Figure 4. Stability for aqueous suspension of metal oxides and carbonates in the presence of Ingevity’s kraft lignin products.
Achieve the highest crop yield with pine-based technology
As the world's largest producer of kraft lignosulfonates, Ingevity is committed to quality, consistency and control in the manufacturing of dispersants and surfactant systems. The incorporation of Ingevity’s kraft lignin products into micronutrient formulations and processes not only protects micronutrients from oxidization or precipitation, but also remediates leaf burn and extends the absorption time on the crop without threatening the environment. Ingevity kraft lignin products allow farmers to formulate low-viscosity and high-solid concentration micronutrient products, rendering cost savings and improving field performance.
Ingevity also introduced a bio-based line of sticker adjuvants under the name AltaHance® that are beneficial for micronutrient applications. AltaHance products provide tunable rainfastness, accelerated spreading, increased penetration, and high performance under challenging conditions. Learn more about these products in the recent ArgoPages feature “Bio-based adjuvants: The future of sustainable agriculture.”
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This article was initially published in AgroPages '2020 Biologicals Special' magazine. Download it to read more articles.