Tim M. Shaver

Evaluation of two crop canopy sensors for nitrogen variability determination in irrigated maize

Advances in precision agriculture technology have led to the development of ground-based active remote sensors that can determine normalized difference vegetation index (NDVI). Studies have shown that NDVI is highly related to leaf nitrogen (N) content in maize (Zea mays L.). Remotely sensed NDVI can provide valuable information regarding in-field N variability and significant relationships between sensor NDVI and maize grain yield have been reported. While numerous studies have been conducted using active sensors, none have focused on the comparative effectiveness of these sensors in maize under semi-arid irrigated field conditions. Therefore, the objectives of this study were (1) to determine the performance of two active remote sensors by determining each sensor’s NDVI relationship with maize N status and grain yield as driven by different N rates in a semi-arid irrigated environment and, (2) to determine if inclusion of ancillary soil or plant data (soil NO3 concentration, leaf N concentration, SPAD chlorophyll and plant height) would affect these relationships. Results indicated that NDVI readings from both sensors had high r2 values with applied N rate and grain yield at the V12 and V14 maize growth stages. However, no single or multiple regression using soil or plant variables substantially increased the r2 over using NDVI alone. Overall, both sensors performed well in the determination of N variability in irrigated maize at the V12 and V14 growth stages and either sensor could be an important tool to aid precision N management.

Soil organic carbon: The value to soil properties

Maintaining or improving soil properties is becoming increasingly important to sustain modern agriculture under increasing demands to preserve biodiversity and environmental quality. Enhancing the inherent capacity of a soil to buffer changes against anthropogenic stresses and extreme climatic events such as droughts, intense rainstorms, heat waves, and floods is also a priority. Managing soil organic carbon (SOC) through optimized management practices is one strategy to enhance soil ecosystem services. Increasing organic C storage in the soil not only sequesters atmospheric C but often enhances soil physical, chemical, and biological processes and properties. Soil organic C has been widely discussed in terms of C sequestration, but its benefits on soil processes and properties have received less attention in recent years. Thus, this article discusses (1) the value of SOC to soil properties and (2) potential for increasing SOC through management. SOIL CARBON DYNAMICS The balance between C inputs and outputs is important to SOC change. Inputs include aboveground and belowground crop residues, animal manure, compost, and others, whereas outputs are losses through water and wind erosion, gas fluxes associated with microbial and plant respiration, and deep leaching. How fast residues decompose following the well-known exponential decay function depends…

Corn residue stocking rate affects cattle performance but not subsequent grain yield.

This study investigated effects of stocking rate on cattle performance, quality and quantity of corn residue, and impact of residue removal on grain yield for 5 yr at the University of Nebraska - Lincoln West Central Water Resources Field Laboratory near Brule, NE. Four removal treatments-1) no removal (control), 2) grazing at 2.5 animal unit month (AUM)/ha, 3) grazing at 5.0 AUM/ha, and 4) baling-were applied to a center pivot-irrigated corn field (53 ha). The field was divided into eight 6.6-ha paddocks to which replicated treatments were assigned. Samples of residue were collected in October and March (before and after residue removal) using ten 0.5-m quadrats per treatment replication. Residue was separated into 5 plant parts-stem, cob, leaf, husk, and grain-and analyzed for nutrient content. Esophageally fistulated cattle were used to measure diet quality. Cattle assigned to the 2.5 AUM/ha stocking rate treatment gained more BW ( < 0.01) and BCS ( < 0.01) than cattle assigned to the 5.0 AUM/ha treatment. Leaf contained the most ( < 0.01) CP and husk had the greatest ( < 0.01) in vitro OM disappearance (IVOMD) but the CP and IVOMD of individual plant parts did not differ ( > 0.69) between sampling dates. Amount of total residue was reduced ( < 0.05) by baling and both grazing treatments between October and March but was not different ( > 0.05) in control paddocks between sampling dates. As a proportion of the total residue, stem increased ( < 0.01) and husk decreased ( < 0.01) between October and March. Diet CP content was similar ( = 0.10) between sampling dates for the 2 grazing treatments but IVOMD was greater after grazing in the 2.5 AUM/ha grazing treatment ( = 0.04). Subsequent grain yields were not different ( = 0.16) across all 4 residue removal treatments. At the proper stocking rate, corn residue grazing results in acceptable animal performance without negatively impacting subsequent corn grain production.

Economic Return versus Crop Water Productivity of Maize for Various Nitrogen Rates under Full Irrigation, Limited Irrigation, and Rainfed Settings in South Central Nebraska

AbstractField research was conducted at the University of Nebraska-Lincoln South Central Agricultural Laboratory (SCAL) located near Clay Center, NE, in the growing seasons of 2011 to 2014. A partial economic analysis was conducted for maize (Zea mays L.) at nitrogen (N) fertilizer treatments of 0, 84, 140, 196, and 252  kg ha−1 under full irrigation (FIT), limited irrigation (75% FIT), and rainfed settings for all growing seasons and then compared to crop water productivity (CWP) measured as crop water use efficiency (CWUE) and irrigation water use efficiency (IWUE). Nitrogen fertilizer increased CWUE and IWUE in all growing seasons. The CWUE values ranged from 0.90 to 2.81  kg m−3 and the IWUE values ranged from −1.01 to 3.24  kg m−3. Operational costs and net income varied among treatments and across years. Irrigation and N fertilizer rate had an interacting effect (P0.05<0.05) on both gross and net income in 2011, 2012, and 2013. Net income was maximized under rainfed settings with a N fertilizer rate...

EVALUATION OF TWO CROP CANOPY SENSORS FOR NITROGEN RECOMMENDATIONS IN IRRIGATED MAIZE

Crop canopy sensors can provide valuable information about in-field nitrogen (N) variability in maize (Zea mays L.) and can serve as the basis for in-season N recommendations. However, few studies have been conducted to determine how the sensors compare. Therefore, a study was conducted using the two most prominent crop canopy sensors (NTechs GreenSeeker™ red and Holland Scientifics Crop Circle™ amber) to determine if the different sensors recommended different amounts of N at the V12 maize growth stage. Results show that each sensor recommended the same amount of N at the V12 growth stage (N recommendations by sensor were not significantly different). The N algorithms developed for each sensor also calculated unbiased N recommendations suggesting that the methodology of algorithm development was valid as was the estimate of required N at maize growth stage V12. Therefore, both crop canopy sensors performed equally in terms of N recommendations in this study.

Effects of Crop Residue Removal on Soil Water Content and Yield of Deficit-Irrigated Soybean

Reduced tillage, with more crop residue remaining on the soil surface, is believed to conserve water, especially in arid and semi-arid climates. However, the magnitude of water conservation is not clear. An experiment was conducted to study the effect of crop residue removal on soil water content, soil quality, and crop yield at North Platte, Nebraska. The same field plots were planted to soybean (Glycine max) in 2009 and 2010. There were two treatments: residue-covered soil and bare soil. Residue (mostly corn residue in 2009 and mostly soybean residue in 2010) was removed every spring from the same plots using a flail chopper and subsequent hand-raking. The experiment consisted of eight, 12.2 m × 12.2 m, plots (two treatments with four replications each). Soybeans were sprinkler-irrigated, but purposely water-stressed, so that any water conservation in the residue-covered plots might translate into higher yields. After four years of residue removal, soil organic matter content and soil residual nitrate nitrogen were significantly smaller, and soil pH was significantly greater, in the bare-soil plots compared to the residue-covered plots. The residue-covered soil held approximately 90 mm more water in the top 1.83 m compared to the bare soil near the end of the 2009 growing season. In addition, mean soybean yield was 4.5 Mg ha-1 in the residue-covered plots, compared to 3.9 Mg ha-1 in the bare-soil plots. Using two crop production functions, it is estimated that between 74 and 91 mm of irrigation water would have been required to produce this extra 0.6 Mg ha-1. In 2010, mean soybean yield was 3.8 Mg ha-1 in the residue-covered plots, compared to 3.3 Mg ha-1 in the bare-soil plots. Between 64 and 79 mm of irrigation water would have been required to produce this extra 0.5 Mg ha-1. In both years, several processes may have contributed to the differences observed: (1) greater evaporation of water from the soil in the bare-soil treatment, and (2) greater transpiration by plants in the bare-soil treatment in the beginning of the growing season as a result of more vegetative growth due to higher soil temperatures in the bare-soil treatment.

Effects of 5 years of corn residue grazing and baling on nitrogen cycling, soil compaction, and wind erosion potential

Abstract Corn residue grazing can provide a valuable and cost effective means of feeding cattle and is a common practice in most corn producing states. Mechanical means of residue removal (baling) is also often practiced as a means of harvesting cattle feed. However, there are concerns about the effects of management practices that remove crop residue on soil processes such as compaction, aggregation, and N cycling. To study these concerns, an experiment with four treatments including control, light grazing, heavy grazing, and baling was carried out for 5 years at the University of Nebraska-Lincoln Water Resources Field Laboratory near Brule, NE. Soil penetration resistance was measured after 3, 4, and 5 years of residue removal. Wind erodible fraction, mean weight diameter of dry aggregates, and soil total N were measured after 5 years. Corn yields were determined throughout the study. Results indicate that light grazing showed little or no difference from the no residue removal treatment, but heavy grazing and baled treatments often had higher penetration resistance, indicating that high rates of residue removal may increase risks of soil compaction. However, compaction did not appear to be cumulative over time. No significant differences were observed in wind erodible fraction and dry aggregate mean weight diameter. However, there were trends that suggest heavy grazing and baling may, in the long term, reduce dry aggregate stability, increasing wind erosion potential. Results also show that in the surface 0–2.5 cm grazing animals may increase soil total N and that baling residue may decrease soil N content. There was no impact on corn yields throughout the study. Overall, corn residue grazing and baling appear to have little or no adverse effects on soil compaction, aggregation, or nitrogen cycling after 5 years.

Crop canopy sensor orientation for late season nitrogen determination in corn

ABSTRACT Increasing nitrogen use efficiency (NUE) in irrigated corn production is of great importance to overall agricultural sustainability. Studies have shown that crop canopy sensors can aid in this pursuit as they allow for the determination of nitrogen (N) requirements in split applications later in the growing season. Fertigation can also increase NUE as many split applications can be conducted. If crop canopy sensors could be used to direct N fertigation rates, overall NUE may be increased even further. However, in some cases, N differences may need to be determined later in the growing season after corn has tasseled, which can cause issues with crop canopy sensor readings. Therefore, a study was initiated to evaluate the potential of a crop canopy sensor to differentiate between N levels at two corn (Zea mays) growth stages (R1 and R3) after the corn had tasseled. The sensor was placed in three orientations to evaluate which orientation best determined the corn N status across two sensor-calculated indices while avoiding taking measurements involving the corn tassel. These orientations were (1) nadir, between corn rows (above canopy), (2) 45° off nadir within the corn canopy (below corn tassel), and (3) 90° off nadir within the corn canopy (below corn tassel). The results of this study show that N differences in late season corn can be determined by utilizing crop canopy sensors in an inter-row orientation. Results also show that the red edge normalized difference vegetation index (ReNDVI) index is superior to the normalized difference vegetation index (NDVI) index for late season N determinations in corn. These results suggest that crop canopy sensors could be an effective tool for determining N requirements of corn late in the growing season.

Effects of nitrogen application frequency via subsurface drip irrigation on corn development and grain yield

ABSTRACT Subsurface drip irrigation (SDI) has not only potential for water conservation, but also for improving nutrient use efficiency. Two nitrogen (N) application frequencies (every week versus every two weeks, via SDI) were compared in 2012 and 2013 on a Cozad silt loam in North Platte, Nebraska. The weekly treatment was fertigated every week for seven weeks in a row; the bi-weekly treatment was fertigated in weeks 1, 3, 5 and 7. Both treatments received the same total amount of N. There was a positive grain yield response to N application, but no advantage was found to a greater frequency of N application. Corn (Zea mays L.) grain yields and other indicators of corn growth and development (canopy-intercepted light, vegetation indices, indicators of chlorophyll content of corn plant leaves) were not affected by N application frequency.

Variable rate irrigation and nitrogen fertilization of maize across landscape positions

Interactions of water and nitrogen (N) supply for crop production can be quite complex across field landscapes. The availability of variable rate fertilization systems, and now variable rate irrigation systems, gives crop producers the opportunity to adjust inputs of water and N according to variation in soil properties. A study conducted across Nebraska, USA, evaluated interactions of water and N supply with landscape features for irrigated maize in 2011 and 2012. Crop yield response to treatments varied with year, as 2012 experienced severe drought conditions. There was evidence from one site/year that irrigation water use efficiency and agronomic efficiency were correlated, with lower productivity areas of fields requiring different levels of water and N than more productive areas.