Maharjan Current Research

Greenhouse Growing

Re-use and Recycling of Industrial By-product

The Western Sugar processing plant at Scottsbluff, NE produces a significant amount of high-carbon char (char, henceforth) as a by-product on a regular basis. This char contains around 30% total C in addition to many essential plant nutrients (N, P, K, Ca, Mg, S, Zn, Fe, Mn, Cu, B, Cl, and Mo). Because of its quality and composition, this product offers potential as a soil amendment to restore soil C levels, improve soil quality, and enhance crop production. Particularly in semiarid regions such as in western Nebraska, where soils are generally low in soil organic matter or soil C due to intensive farming, wind and water erosion, application of soil amendments with such high C concentration may improve soil quality and crop production.

For many considerations, it is important to promote and practice stewardship of such a finite resource as soil, and conserve and improve it, particularly in semiarid regions such as in Western Nebraska. We are testing the hypothesis that this high-C char might be a potential soil amendment.

Manure Management

Integrated crop-livestock systems offer a tremendous potential to optimize use of finite resources such as water, nutrients, and energy and diversify farm ecosystems. Such integrated systems can be more economically competitive and environmentally sustainable than prevailing specialized production systems. In manure management, depending on method and duration of storage, there is a potential risk of significant loss of valuable nutrient such as nitrogen. Feedlot manure removed from pens in the spring and summer is often stored until crops are harvested in the fall before field application can occur. Methods of handling and storing manure have an impact on nutrient recoveries and manure characteristics.

The recommended C:N ratio for feedlot and dairy manure is between 25 and 40:1. At lower C:N ratios, ammonia losses are increased because the energy substrate for microbial growth is limiting. Between 60% and 75% of the N consumed by the animal is lost to volatilization after being excreted until it is applied to fields. Increasing the C:N ratio of feedlot manure has been successful in reducing the amount of N lost from the feedlot. Since the char from Western Sugar contains around 30% C, it might shift microbial process towards N conservation in manure when mixed in with manure. Additionally, the char might also physically retain N by electrostatic adsorption to its exchange sites. With this assumption in mind, a study was initiated in 2017.

Percent ammonia emissions
Percent ammonia emissions from total manure-ammonia in each component of livestock operation (EPA National Emissions Estimates, 2005).

Soil Fertility Management

Abundant precipitation increased wheat production across Nebraska in 2016 and 2017 leading to record yields. However, low protein levels offset potential for financial gains and in some cases substantial economic losses. Yield protein in wheat is directly related to the ability of wheat to uptake nitrogen (N) from the soil and translocate it to the grain. Low protein levels in 2016 and 2017 reduced the value of the NE wheat crop, raised the need to review the current fertility management recommendations and provide updates that better align with today’s wheat genetics and changing climatic conditions. Two-year field trials across Nebraska will evaluate the effects of N and S on wheat yield and quality. The N treatment effect on grain yield and quality will also be evaluated at different precipitation regimes to determine N management that can be adjusted to available soil moisture in order to avert protein reduction. In-season crop status assessment using crop sensor, which is proven to work in corn, will be explored as a tool for wheat fertility management to aid NE wheat.

Setup to measure  N losses.

Laboratory set-up to measure N2O, NO3 and NO3- losses.

Suction cup lysimeter
Suction cup lysimeter is installed at 5 feet depth in soil to collect soil solution to analyze for nitrate-N that would potentially leach.
Suction cup lysimeter.

Environmental Nutrient Losses (Greenhouse gas emission, air and water quality)

Nitrogen (N) fertilizer use will continue to increase as we strive for food, energy, and fiber security for the world’s growing population. However, crop N uptake efficiency is generally less than 50% of applied N, leaving a significant amount of N susceptible to loss from agricultural soils. Inefficient crop utilization of N can reduce producer profitability, and N lost from agricultural land in any form, be it nitrate, ammonia, or nitrous oxide, has adverse ecological impacts on environmental quality. Calls to achieve environmental sustainability in agricultural production systems will only intensify.

Nitrous oxide (N2O) is a major greenhouse gas (GHG) and also the single most important ozone-depleting emission. Agricultural activities are responsible for 10-12% of total anthropogenic GHG emissions and more than half of agricultural GHG emissions are derived from N2O. Agricultural N2O emissions are linked to soil management and application of N fertilizers. Leaching losses of N as nitrate (NO3-) can be a major limitation to crop production in irrigated and/or coarse-textured soils. Nitrate is a major groundwater contaminant. Nitrogen lost from fertilized fields through NO3- leaching can also contribute to N2O emissions by conversion of NO3- to N2O in a receiving aquatic ecosystem. Fertilizer-derived ammonia (NH3) losses also can be significant, particularly in drier agroecosytems. As volatilized NH3 from fertilized agricultural land is re-deposited to the ground, it can acidify soils, become a secondary source of N2O emission, and promote eutrophication of surface water bodies.

Greenhouse gas sampling in the field.
Greenhouse gas sampling in the field.

Crop Sensing

Optimization of nitrogen (N) management in agriculture is key to addressing economic and environmental issues associated with N fertilization. Presence of in-field spatial variability makes the task more challenging. Therefore, it is important to be able to detect variability in crop N status within a field and that has been studied in depth. A strong relationship between total chlorophyll content in a maize canopy and the crop N status has been well established. Recent research into detecting crop N status has focused on non-destructive sampling techniques. Non-destructive techniques focus on remote sensing to correlate with and quantify canopy chlorophyll content. Studies have suggested different strategies for in-season N management using remote sensing that monitor differences in crop N status by evaluating relative crop response to applied N. In-season N application practices guided by canopy sensor is yet to explore in many crops grown in semi-arid western Nebraska.

Knorr-Holden Plots sign
SB_experiment_station in 1912

Historic Knorr-Holden Plot

The historic Knorr-Holden experimental site near Mitchell, Nebraska, US is the oldest irrigated maize plot in North America and possibly the world. It has over 100-year old manure and urea treatment plots under furrow-irrigated continuous maize. The N fertilization alone was capable of restoring most of production capacity of the soil. The practice of manuring greatly improved the physical condition of the soil. After a full century of the experiment, in 2014, N treatments were revised and a few extra N treatment plots was added. Now, the experiment is randomized complete block design with four replications. The main factor is N treatment, which includes urea-N treatments of 0, 56, 112, 168, 224 and 280 kg N ha-1 in non-manured plots and urea-N treatments of 0, 56, 112, 168 kg N ha-1 and N treatments based on spring soil test (SST) and crop sensing at V6 (CS) in manured plots. Manure plots received 67 Mg ha-1 of cattle manure in 2014 and will continue at same rate every four year.