Allen V. Barker

The effects of water availability in the soil and fertilizer application often strongly affect crop growth. Tuber dry matter yield and physiological characteristics of potato (Solanum tuberosum L.) were investigated under different irrigation regimes (S₁, full irrigation, 100% of water requirement; S_2, 75% of water requirement; and S_3, 50% of water requirement). Nitrogen treatments were four amounts of urea (N_1, providing 100% of N requirement; N_2, 66% of N requirement; and N_3, 33% of N requirement, and N₄, 0 kg N/ha. Drought stress with 50% of the water requirement and limiting nitrogen fertilizer application suppressed the number and weights of tubers per plant. The yield of marketable tubers in S₁ and S₂ treatments was not significantly different. Treatments N₁, N₂, and N₃ increased the yield of marketable tubers by 37, 33 and 12%, respectively, compared to N₄. Drought stress (S₃) increased the percentage of dry matter, but nitrogen fertilization did not cause a significant change. Drought stress (S₃) increased the amount of soluble sugars in tubers and proline in leaves; however, the amounts of soluble sugars and proline were unchanged by increased nitrogen fertilization. Full irrigation and meeting of nitrogen requirements of potatoes led to high chlorophyll concentrations in leaves. Under drought stress (S₃) and increasing nitrogen, the starch content of tubers was suppressed. The amount of nitrate in the tubers was not affected by irrigation treatments, but was raised by increasing nitrogen fertilization. Irrigation of 75% or more combined with fertilizer application of 66%, was an appropriate treatment for potato production.

Poor germination and the length of time required for the growth of seedlings appropriate for planting in the farm affect the cultivation of medicinal plants such as yarrow (Achillea millefolium L). This study investigated the abilities of different concentrations of gibberellic acid (GA₃) and potassium nitrate (KNO₃), mechanical scarification, and hydropriming to improve seed germination and dormancy release in yarrow. Seeds were germinated on filter paper in Petri dishes and supplemented with 0, 100, 200, 400, or 800 mg L⁻¹ GA_3; 0%, 0.2%, 0.5%, 1.0%, or 2.0% w/v KNO₃; 0, 24, or 48 h of hydropriming; and mechanical scarification. Seed priming with GA₃ (800 mg L⁻¹) or 1% KNO₃ at 48 h priming time improved the mean daily germination. Application of 1% KNO₃ had the highest seed germination around 91%. Use of 0.5% KNO₃ in 48 h priming time increased seedling length approximately 52% compared with unprimed seeds. Combinations of scarification and hydropriming increased germination. The use of priming with KNO₃ at 48 h priming time was effective in improving seed germination.

Organic fertilizers might have prominent effects on lavender (Lavandula angustifolia Mill.) plant growth and secondary metabolites composition. A field study was conducted to assess the responses of biomass yield, nutrients, and essential oil components of lavender to different organic fertilizers. The effect of fertilizer treatments included changing the amounts of cow manure (0–40 tonne/ha) and vermicompost (0–15 tonne/ha). The fertilizers enhanced the total area and dry matter of the leaves by 40% with cow manure and 62% with compost compared to no fertilization. The essential oil yield increased by 70% after treatment with cow manure. The highest change in the essential oil composition was marked in the oxygenate monoterpenes such as 1,8-cineole, followed by borneol, and camphor. The highest percentage of 1,8-cineole was achieved with a mix of both organic fertilizers. In addition, this combination was able to increase the leaf N concentration by 43% above the unfertilized treatment. These results showed that the use of combined fertilizers enhanced the leaf dry matter and improved the plant nutrient value and essential oil constituents.

Leaf morphology and anatomy are important criteria to evaluate plant tolerance to salinity stress. Therefore, in this study the morphophysiological responses of strawberry (Fragaria’× anansa Duchesne “Camarosa”) plants treated with nanosilicon (nSiO₂) were investigated under salt-stress conditions. The plants in a complete nutrient solution designed for strawberry were exposed to salt stress (0, 25, or 50 mM NaCl) and treated with nanosilicon before (0, 50, or 100 mg L⁻¹) or after (0 or 50 mg L⁻¹) floweringConcentrations of sodium (Na), chlorine (Cl), and calcium (Ca) increased in plants exposed to salt stress, whereas silicon (Si), potassium (K), and phosphorus (P) decreased. In the presence of nanosilicon, strawberry plants absorbed K, P, and Ca from the nutrient solution and transferred the nutrients to leaves effectively. Only a little amount of Ca, Cl, or Na was transferred to leaves with presence of nanosilicon. The adverse effects of salinity on phyllochron, flowering, and fruit set, and fruit production parameters were suppressed by application of nanosilicon. Analysis by optical microscopy revealed that salt stress limited the number of parenchyma cells, leaf thickness, epidermis cell thickness, and mesophyll thickness, thereby leading to restrictions in chlorophyll content and photosynthetic efficiency. Nanosilicon application reduced negative effects of salinity by improving cell wall thickness, providing higher content of water, and leading to increased chlorophyll content and fluorescence. Overall, these observations indicated that application of nanosilicon can suppress the adverse effect of salinity on anatomical and physiological changes of strawberry plants.

A one-time, large application of biochar (charcoal) could increase soil carbon (C) content and improve overall soil quality. It is known that nematodes have effects on soil organic matter and nutrient cycling and are plant diseases; moreover, nematodes affect nutrient mobilization in C-rich soil conditions; however, information is scant on the effect of biochar addition on nematode communities. Therefore, the objective of this field study was to evaluate the influence of sugar maple hardwood biochar on soil nematode communities and assess the relation among soil nematode communities and soil nutrient concentrations. Nematode communities were sampled and identified in soils without biochar application and soil amended with an application of 8% by weight (equivalent to 160 Mg ha⁻¹). The application of 8% biochar did not change the abundance of nematodes but affected some nematode communities. Compared to the unamended soil, biochar-amended soil had lower plant-parasitic nematode populations and higher abundance of predatory nematodes. The Shannon diversity index (H’) was lower, and the maturity index (MI) was higher with a mean value of 2.38 with biochar addition compared to 2.21 in unamended plots. Higher soil acidity and addition of substantial amounts of magnesium, calcium, potassium, and manganese in the biochar-amended soils were recorded after biochar application.

The objective of this project was to investigate if integrating cover crops into the lettuce (Lactuca sativa L.) production can control weeds and improve various components of soil health. A two-year field study was conducted at the research farm of the University of Mohaghegh Ardabili, Ardabil, Iran, during the 2017 and 2018 growing seasons. In this study, we used monoculture, two-way, and a three-way mixture of barley, chickling pea, and buckwheat cover crops and no cover crop (local weeds). Sole barley cover crop produced the highest biomass in both growing seasons. The barley and buckwheat mixture in 2017 and barley and chickling pea in 2018 were most efficient in suppressing weeds. The dominant weeds included lambsquarters, redwood pigweed, and charlock mustard. Although the number of earthworms was more in the sole barley plots, the microbial population was highest in the three-way cover crop mixture. Soil carbon improved in the three-way cover crops by 12%; however, the differences amongst cover crop treatments were not statistically significant. Bulk density was reduced by 13% and water infiltration rate reduced by half averaged across cover crop treatments compared to no cover crop. Lettuce fresh weight increased in all cover crop treatments; however, a mixture of chickling pea and buckwheat cover crop improved the yield of lettuce by 17.8%, compared with the no cover crop.

Effects of varying the ammonium:nitrate ratios in nutrient solutions and effects of calcium carbonate buffering on plant mass and accumulation of potassium and calcium were studied with two lettuce (Lactuca sativa L.) cultivars, Two Star and Red Deer Tongue, in a greenhouse hydroponics experiment. The supply of ammonium-N ranged from 0% to 100% of the total nitrogen in the nutrient solution at 0.015 M total N supplied as nitrate and ammonium. Proportions of ammonium-N greater than 50% of total N nutrition severely curtailed growth and calcium and potassium accumulation for both cultivars. Growth and composition of the two cultivars did not differ in response to nitrogen nutrition. The acidity of the nutrient solution increased as the proportion of ammonium increased. Application of calcium carbonate buffering improved growth in solutions containing ammonium, but plants did not attain the amount of growth and nutrient accumulation achieved with solely nitrate nutrition.

Dairy farmers in the northeast face challenges in the application of manure in fall and on-time planting of cool-season grasses to maximize recovery of residual N and nutrients released from fall applied manure. Ammonia emission from animal manure is a serious environmental concern and can be reduced if cover crop is integrated in the farming system. On-time planting of cover crops can reduce ammonia volatilization from fall, surface-applied manure, and prevents N loss to leaching. A two-year study was conducted in 2015 and 2016 to investigate if time of planting of winter annual rye (Secale cereale L.) along with late fall application of manure when air temperature is low can influence ammonia emission and preserve nitrogen (N) to meet the N requirement of forage rape. Three planting dates (16 September, 30 September, and 14 October) of rye cover crop with two manure application treatments including late-fall application and no manure were assessed for mitigating ammonia volatilization, and also yield and recovery of N by forage rape (Brassica napus L.). The highest rates of ammonia volatilization were detected in the first 24 hours after manure spreading regardless of the treatment. The result indicated that cover crop use significantly limited volatilization compared with no cover crop. The earliest planting date produced 3823 kg ha⁻¹ dry matter of winter rye cover crop that was 16 and 35 percent higher than second and third dates of planting, respectively. The manured cover crop accumulated 132 kg N ha⁻¹ when planted early. However, biomass yield of forage rape was more when planted after all cover crop treatments with manure application. Prior to forage planting, the nitrate-N content in all three soil depths (0–20, 20–40, and 40–60 cm) in the plots with manure was higher than plots with no manure. No significant differences in forage rape yield was detected among winter rye planting dates; however, forage rape planted after winter rye was higher than after no-cover crop. The results of this study suggest that when immediate incorporation of manure into soil is not feasible, establishing cover crop early and then applying manure in the late fall, is a practical management to limit nonpoint source pollution from ammonia loss.

Interest is rising in amending agricultural soils with carbon-rich materials such as charcoal to improve soil fertility. The objectives of this field study were to evaluate sugar maple hardwood charcoal (biochar) as a soil amendment. The design of the experiment was split-plot with five replications, repeated over two growing seasons with sweet corn (Zea mays L.) production. Main plots were allocated to five application amounts of biochar including 0%, 2%, 4%, 6%, and 8% by weight (0, 40, 80, 120, and 160 Mg ha⁻¹, respectively). Sub-plots consisted of applications of 0 or 56 kg nitrogen ha⁻¹ as calcium ammonium nitrate. Soil pH increased from pH 5.8 to 6.7 with biochar additions. The percent base saturation was increased due to the retention of calcium, magnesium, and potassium. Soil phosphate availability increased. Sweet corn yield in the biochar-amended plots was depressed except with the 2% application. The result of the study revealed that no more than 2% application of sugar maple hardwood biochar should be applied for sweet corn growth.

Cover crops improve the recovery and recycling of nitrogen and impart weed suppression in crop production. A two-year study with six weekly plantings of cover crops including non-winterkilled species (hairy vetch, Vicia villosa L.; winter rye Secale cereale L.) and winterkilled species (oat, Avena sativa L.; forage radish, Raphanus sativus L.) were assessed for effects on growth of forage rape (Brassica napus L.) and weed suppression. Early planting of cover crops gave the highest biomass and highest nitrogen accumulation. Delaying planting from early-September to mid-October suppressed cover-crop biomass by about 40%. Forage radish produced more biomass in the fall than other cover crops but was winter killed. Spring biomass was highest with rye or vetch. All cover crops suppressed weeds, but suppression was greatest under rye or hairy vetch. Hairy vetch accumulated the largest nitrogen content. Forage rape plants yielded more biomass after a cover crop than after no-cover crop.