The Effect of Humalite on Improving Soil Nitrogen Availability and Plant Nutrient Uptake for Higher Yield and Oil Content in Canola

Abstract

Over the last half-century, the widespread use of synthetic chemical fertilizers has boosted crop yields but caused noticeable environmental damage. In recent years, the application of humic substances to increase plant growth and crop yield has gained considerable interest, largely due to their organic origin and their ability to reduce nutrient losses while enhancing plant nutrient use efficiency. Humalite, found exclusively in large deposits in southern Alberta, Canada, is rich in humic substances and has low levels of unwanted ash and heavy metals, which makes it particularly valuable for agricultural applications. However, its effects on canola, the largest oilseed crop in Canada and the second-largest in the world, have yet to be evaluated. This study investigated the effects of five Humalite rates (0, 200, 400, 800, and 1600 kg ha^-1) in combination with nitrogen, phosphorus, and potassium (NPK) applied at recommended levels, on canola growth, soil nitrogen availability, plant nutrient uptake, photosynthesis, seed yield, seed oil content, and nitrogen use efficiency under controlled environmental conditions. The results demonstrated that Humalite application significantly enhanced soil nitrogen availability, uptake of macro- and micronutrients (N, P, K, S, Mg, Mn, B, Fe and Zn), shoot and root biomass, net photosynthesis, and water use efficiency as compared to the NPK alone treatment. The application of Humalite also led to increased seed yield, seed oil content, and nitrogen use efficiency. Taken together, Humalite could serve as an effective organic soil amendment to enhance canola growth and yield while enhancing fertilizer use efficiency.

FIGURE 1

Photographs and boxplots of the shoot and root growth parameters exhibiting the median values and variability of canola plants grown under varying rates of Humalite and NPK at the recommended rate. Plants were photographed at 6 weeks post‐planting. The photographs on the top row represent (A) the shoot and in the bottom row (B) the roots. The images from left to right order representing plants from control without NPK and Humalite, NPK without Humalite, NPK with 200 kg ha⁻¹ Humalite, NPK with 400 kg ha⁻¹ Humalite, NPK with 800 kg ha⁻¹ Humalite, and NPK with 1600 kg ha⁻¹ Humalite. The scale bar in images of both shoot and root = 5 cm. The graphs in the panels include (C) shoot dry weight, (D) root dry weight, and (E) total plant dry weight. The boxplots illustrate the median and interquartile ranges (n = 6). The upper line of each box represents the third quartile (Q3), while the lower line indicates the first quartile (Q1). Significant differences among the treatments, as determined by the Fisher LSD test (p ≤ 0.05), are indicated by different letters above the boxes.

FIGURE 2

Boxplots of gas exchange parameters exhibiting the median values and variability of canola plants grown under varying rates of Humalite and NPK at the recommended rate. The graphs in the panels include (A) photosynthesis rate, (B) intercellular CO₂ concentration, and (C) water use efficiency. The boxplots illustrate the median and interquartile ranges (n = 12). The upper line of each box represents the third quartile (Q3), while the lower line indicates the first quartile (Q1). Significant differences among the treatments, as determined by the Fisher LSD test (p ≤ 0.05), are indicated by different letters above the boxes.

FIGURE 3

Bar graph showing the effect of varying rates of Humalite and NPK at the recommended rate on total soil nitrogen, nitrate and ammonium availability determined using the plant root simulator probes at 4 and 6 weeks of growth. The graphs in the panels include (A) total available nitrogen, (B) nitrate availability, and (C) ammonium availability. Significant differences among the treatments, as determined by the Fisher LSD test (p ≤ 0.05), are indicated by different letters above the bars. Values correspond to the means ± SD (n = 6).

FIGURE 4

Boxplots of macro‐ and micronutrient content of canola plants exhibiting the median values and variability of the canola plants grown under varying rates of Humalite and NPK at the recommended rate. The graphs in the panels include total shoot (A) nitrogen, (B) phosphorus, (C) potassium, (D) sulfur, (E) magnesium, (F) manganese, (G) boron, (H) zinc, and (I) iron. The boxplots illustrate the median and interquartile ranges (n = 6). The upper line of each box represents the third quartile (Q3), while the lower line indicates the first quartile (Q1). Significant differences among the treatments, as determined by the Fisher LSD test (p ≤ 0.05), are indicated by different letters above the boxes.

FIGURE 5

Boxplots of seed yield, oil concentration, oil content and nitrogen use efficiency exhibiting the median values and variability of canola plants grown under varying rates of Humalite and NPK at the recommended rate. The graphs in the panels include (A) seed weight, (B) oil concentration, (C) total oil content, and (D) nitrogen use efficiency. The boxplots illustrate the median and interquartile ranges (n = 12). The upper line of each box represents the third quartile (Q3), while the lower line indicates the first quartile (Q1). Significant differences among the treatments, as determined by the Fisher LSD test (p ≤ 0.05), are indicated by different letters above the boxes.

FIGURE 6

Principal component analysis of plant growth and yield parameters measured at flowering and seed maturity stages. (A) PCA biplot for variables measured in plants grown to the flowering stage, including total soil nitrogen (TN) availability, shoot dry weight (SDW), root dry weight (RDW), total plant dry weight (TPDW), and nutrient content (nitrogen, phosphorus, and potassium; NPK). (B) PCA biplot for variables measured in plants grown to the seed maturity stage, including photosynthesis rate, intercellular CO₂ concentration (Ci), water use efficiency (WUE), seed weight, oil content, and nitrogen use efficiency (NUE).