Peter C. Scharf

Soil and plant tests to predict optimum nitrogen rates for corn

Optimum fertilizer nitrogen (N) rates are highly variable from one production corn (Zea mays L.) field to another, but producers usually use about the same N rate over their whole farm. Matching N application rates to actual crop need could have both economic and environmental benefits. The objectives of this research were to evaluate soil and plant tests for their ability to predict optimum N rates across a range of production cornfields in Missouri, and to evaluate the economic performance of recommendation systems based on these measurements. Yield response to N was measured in each experiment, along with soil mineral N measurements (planting and sidedress), tissue N at sidedress time, and chlorophyll meter reading at sidedress time. Optimum N fertilizer rates were fairly evenly spread from 0 to 235 kg N ha−1 in these sixteen experiments. Soil N measurements, tissue N at sidedress, and chlorophyll meter reading at sidedress were all clearly related to optimum N rate—the higher the test result, the lower the optimum N rate. Plant measurements (tissue N content and chlorophyll meter reading) were more strongly related to optimum N rate than were any of the soil measurements. Only two of the recommendation systems tested significantly increased profit (by

Soybean Yield Responds Minimally to Nitrogen Applications in Missouri

17 to 20 ha−1) relative to N rates used by producers in these fields: 1) subtracting both traditional credits (for manure, alfalfa [Medicago sativa L.], or soybean [Glycine max L.]) and a preplant soil nitrate credit from current University of Missouri recommendations, or 2) using sidedress tissue N content to predict sidedress N rate. Three other systems reduced N rates significantly relative to producer N rates without reducing profits: 1) chlorophyll meter to predict sidedress N rate, 2) sidedress soil nitrate test with the critical value adjusted for wet springs, and 3) University of Missouri recommendations with history credits only. *Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 12,767.

Macronutrient concentrations of soybean infected with soybean cyst nematode

Interest among soybean (Glycine max Merr.) producers in using nitrogen (N) fertilizer for soybean production has been stimulated by recent reports of substantial yield responses to N. We conducted 48 experiments measuring soybean yield response to N over a broad range of soils, genetics, and weather. Nitrogen fertilizer was applied either preplant or at the beginning pod stage. Minimal soybean yield response to N was found. Small responses (approx. 1 bu/acre) to N applied at planting were observed in two groups of experiments: experiments with soil salt pH < 6.0 and experiments with soil nitrate-N < 50 lb/acre to a 2-foot depth. Of five experiments with yields > 60 bu/acre, two responded to N at planting. No yield response to N applied at the beginning pod stage was seen for any group of experiments sharing specific soil or crop factors. Introduction Soybeans contain high levels of protein, and therefore of nitrogen. A 50bu/acre soybean crop contains as much N as a 225-bu/acre corn crop. Soybean plants fix atmospheric N2, but fixation is minimal for the first month after planting even under conditions of low N availability. High soil N availability (as nitrate) can inhibit formation of nodules (5) and delay N fixation further or even suppress it through the whole season (4). The lag in formation and activation of the N2-fixing system suggests that soybean growth might sometimes be N-limited early in the growing season. During early growth, the plant relies on soil nitrate, along with the N stored in the seed. When soil nitrate is low, preplant application of N fertilizer could increase soybean growth and yield. This is exactly what was observed by Lamb et al. (6), who found large yield responses to N fertilizer (average about 5 bu/acre) when soil nitrate was below 75 lb/acre in the top two feet, and little response when soil nitrate was above this level. However, when soil N availability is adequate, preplant N fertilizer applications might have a detrimental effect by suppressing nodulation. Nitrogen fertilizer applications later in the season may supplement N inputs from fixation while minimizing inhibitory effects on fixation (2). Wesley et al. (9) suggest that at high yield levels, maximum N2 fixation rates may not be able to keep pace with seed demand for N. They found that irrigated soybean yields were increased by an average of 7 bu/acre (from 55 bu/acre to 62 bu/acre) when N fertilizer was applied at growth stage R3 (beginning pod development). This report has stimulated renewed interest in N fertilization among soybean producers in the midwestern U.S. These are a few of the highlights of the considerable body of research that has been devoted to studying N fertilizer applications to soybean. Yield response and lack of yield response have both been frequently observed. Understanding the conditions that are conducive to yield response would aid in making the most profitable decision regarding N fertilization of soybean. We graphically combined results reported from 58 previous experiments measuring soybean yield response to N to look for factors favoring yield responses. This analysis suggested that yield increases are favored by: Crop Management 17 November 2003 · yield levels above 60 bu/acre · application timing at the beginning pod stage · 2-ft soil nitrate < 75 lb/acre · soil pH > 7.5 · irrigation Our objective was to estimate the frequency of soybean yield response to N in Missouri and to elucidate the effects of yield level, application timing, soil nitrate, and soil pH on this response. Methods: 48 Experiments Across Six Years in Missouri We conducted 48 experiments from 1996 to 2001 to measure the effects of N fertilizer application on soybean yield in Missouri. Twenty-eight of the experiments were in producer fields, and twenty were conducted at five research farms. Experimental locations are shown in Fig. 1. All major soybean-growing regions of Missouri are represented, along with a broad range of soils typically used for soybean production. One well-adapted cultivar was chosen for each of the 48 experiments. Cultivars used at more than one location included Asgrow 3701, Pioneer 93B82, Novartis S46-W8, Pioneer 9594, Asgrow 3302, Pioneer 94B01, Asgrow 4301, and Asgrow 4403. A seeding rate of 174,000 seeds per acre planted in 30-inch rows was used for all experiments. Average planting date was May 14, and ranged from May 1 to June 12. Some form of tillage was used in 38 of the 48 experiments, and 10 of 48 received sprinkler irrigation. The previous crop was corn in most experiments, with previous crops of soybean, rice, and cotton in a few locations. For 40 experiments in 2000 and 2001 (including all 28 experiments in producer fields), there were three N application treatments: untreated control, N applied at planting, or N applied at growth stage R3 (beginning pod development). Nitrogen was hand-applied as ammonium nitrate at a rate of 25 lb of N per acre. This N rate was chosen because our literature survey revealed no significant effect of N rate on yield response to N (380 data points from 58 published experiments with N rates from 20 to 300 lb/acre were used for this analysis), and a low N rate would increase the likelihood of the treatment being economical for producers. A randomized complete block design with five replications was used, but two untreated control plots were included in each Fig. 1. Forty-eight experiments measuring soybean yield response to N fertilizer were spread widely around Missouri. Twenty farms (squares) had experiments in 2000 and 2001. Experiments in producer fields are shown in red; those at experiment stations are shown in green. Fields used in 2001 were different than fields used in 2000. The other eight experiments were conducted at the Bradford Research Center (star) from 1996 to 2001. A wide range of genetics, soils, production practices, and climate were represented. Crop Management 17 November 2003 replication. Plots were 25 ft long by 10 ft (four 30-inch rows) wide. At harvest, plots were trimmed to 20 ft in length, the center two rows of each plot were harvested with a plot combine, and yields were adjusted to 13% moisture. From each experimental area, 15 soil cores were taken to a 3-foot depth (depth increments of 0 to 6, 6 to 12, 12 to 24, and 24 to 36 inches) before planting, mixed, and analyzed for nitrate-N, ammonium-N, and salt pH (measured in a 1:1 paste of soil and 0.01 M calcium chloride) (this is the standard pH measurement for the University of Missouri Soil Testing Lab). The other eight experiments were conducted on the Bradford Research Farm near Columbia, Missouri, and included additional treatments such as additional application timings or forms of N fertilizer. In this report, only results from ammonium nitrate applied at planting or at growth stage R3 are included in accordance with the other 40 experiments. Nitrogen rates ranged from 45 to 90 lb/acre in these experiments. When more than one N rate was used, yield results were combined across N rates. Details of planting, harvest, and experimental design were the same as the group of 40 experiments, except that only four replications were used, and only one untreated control was included in each replication. Soil samples (0to 6-inch) were taken from two of these experiments and analyzed for nitrate-N. Analysis of variance was used to determine whether a significant response to N fertilizer occurred at each experimental location. Linear regression was used to model the relationship between site variables (control yield, soil nitrate-N, soil ammonium-N, soil pH) and the apparent yield response to N (= yield with N yield without N). A t-test was used to test whether yield response to N was different from zero over all experiments and for sub-groups with low soil nitrateN and low soil pH. Yield Levels Average control yield over all 48 experiments was 47.5 bu/acre. This is a good yield for soybean in Missouri and indicates good production practices along with generally favorable growing conditions. The only experimental locations that experienced poor growing conditions were five experiments conducted in southwest Missouri in 2000, where drought stress limited yields to between 25 and 32 bu/acre. Overall Response to N. Overall, minimal yield response to N applications was observed. Average yield response to N applied at planting was 0.5 bu/acre (a t-test indicates 90% probability that this was a true yield response) over the 48 experiments. Average yield response to N applied at the beginning pod stage was -0.01 bu/acre. Delaying N application timing until beginning pod clearly did not enhance soybean yield response to N in our experiments, as we had hypothesized based on our summary from a large group of experiments in the literature. However, the results of that summary were heavily weighted by the large yield increases from a single set of experiments (9) in which N was applied at the beginning pod stage. It would not have been profitable to apply N (either timing) to the whole group of experiments. Recent results from twelve experiments in Minnesota (7) and three experiments in Virginia (3) also found that N applied to soybean at reproductive growth stages was not profitable. We looked for site factors that would help identify and predict fields where soybean yield responded to N. We found evidence that yield response to N applied at planting was more likely where: · soil pH was low (Fig. 2); · soil nitrate was low (Fig. 3). Crop Management 17 November 2003 However, even in these situations, yield response was small and we did not find any compelling economic benefits from N fertilizer applications to soybean in Missouri. Response to N at Sites with Low Soil pH. Yield response to N applied at planting was greater at sites with lower soil pH (Fig. 2) with 85% probability based on regression analysis. Considering only the group of 16 experiments with salt pH less than 6.0 (water pH less t

A Case Study of Environmental Benefits of Sensor-Based Nitrogen Application in Corn

Soybean cultivars (Glycine max(L.) Merr.) infected with soybean cyst nematode (SCN; Heterodera glycinesIchinohe) often show symptoms similar to K deficiency. The objectives of this experiment were to determine if SCN infection affected macronutrient concentrations in soybean seedling vegetative tissues, determine whether increased K fertility can overcome these possible effects, and to determine if these possible effects are localized at the site of infection or expressed systemically throughout the root system. Soybean plants were grown with root systems split into two halves. This allowed differential K (0.2, 2.4 and 6.0 mM K nutrient solutions) and SCN (0 and 15 000 eggs/plant) treatments to be applied to opposite root-halves of the same plant. Thirty days after plants were inoculated with SCN, macronutrient concentrations of shoot and root tissues were determined. Potassium concentration in leaf blades was not affected; but K concentrations in leaf-petiole and stem tissues were increased with SCN infection. Roots infected with SCN contained lower K concentrations than uninfected roots, but only for the 2.4 mM K treatment. Thus, at the medium level of K fertility, SCN reduced K concentration in soybean roots, and increasing K fertility to the high level overcame the effect. Because K concentrations in the shoot tissues were not reduced by SCN infection, above ground portions of the plant may be able to overcome limitations that occur in roots during the first 30 days of infection. Increasing K fertility level in soybean fields may not benefit vegetative growth of soybean infected with SCN.

Corn Production as Affected by Phosphorus Enhancers, Phosphorus Source and Lime

Crop canopy reflectance sensors make it possible to estimate crop N demand and apply appropriate N fertilizer rates at different locations in a field, reducing fertilizer input and associated environmental impacts while maintaining crop yield. Environmental benefits, however, have not been quantified previously. The objective of this study was to estimate the environmental impact of sensor-based N fertilization of corn using model-based environmental Life Cycle Assessment. Nitrogen rate and corn grain yield were measured during a sensor-based, variable N-rate experiment in Lincoln County, MO. Spatially explicit soil properties were derived using a predictive modeling technique based on in-field soil sampling. Soil NO emissions, volatilized NH loss, and soil NO leaching were predicted at 60 discrete field locations using the DeNitrification-DeComposition (DNDC) model. Life cycle cumulative energy consumption, global warming potential (GWP), acidification potential, and eutrophication potential were estimated using model predictions, experimental data, and life cycle data. In this experiment, variable-rate N management reduced total N fertilizer use by 11% without decreasing grain yield. Precision application of N is predicted to have reduced soil NO emissions by 10%, volatilized NH loss by 23%, and NO leaching by 16%, which in turn reduced life cycle nonrenewable energy consumption, GWP, acidification potential, and eutrophication potential by 7, 10, 22, and 16%, respectively. Although mean N losses were reduced, the variations in N losses were increased compared with conventional, uniform N application. Crop canopy sensor-based, variable-rate N fertilization was predicted to increase corn grain N use efficiency while simultaneously reducing total life-cycle energy use, GWP, acidification, and eutrophication.

Influência da direção de semeadura do milho nas variáveis reflectância e índice de vegetação verde normalizado

Prompted by high cost of fertilizer, farmers are investigating ways to enhance the efficiency of phosphorus (P) fertilizers. This study examined the effects of liming application (0 Mg ha -1 and recommended rate), P source [non-treated control and a broadcast application of diammonium phosphate (DAP) or triple superphosphate (TSP)], and the presence or absence of two commercial enhanced efficiency P products (Avail ® and P2O5-Max ® ) on corn (Zea mays L.) production. The study was conducted at Novelty in northeastern Missouri and Portageville in southeastern Missouri. The P enhancers did not affect plant population, silage dry weights, grain moisture, yield, protein, oil, or starch concentrations at either location. At Portageville, P enhancers did not affect plant N, P, K uptake and apparent P recovery efficiency (APRE). At Novelty, neither P enhancer paired with DAP increased P uptake over the non-treated control. TSP treated with Avail

Using a field radiometer to estimate instantaneous sky clearness

The objective of this work was to study the influence of the row direction of corn (Zea mays) on its spectral properties measured in the field, including the green normalized difference vegetation index (Green NDVI). Spectral properties of corn are known to be related to the nitrogen (N) status of the corn and may form the basis for real-time site-specific rates of N application. Row direction effects on spectral properties may be substantial before canopy closure. If so, it will be necessary to account for these effects in order to accurately predict the N need of corn from spectral measurements. Corn was planted directly, with no tillage, in North-South (NS) and East-West (EW) oriented rows. Nitrogen was applied as ammonium nitrate at a rate of 160 kg N ha-1. Reflectance was measured with spectral radiometers placed 30 cm above individual plants. Reflectance and green NDVI were bly dependent on time of day for corn in NS rows, and much less so for corn in EW rows. Reflectance and green NDVI were lower for corn in EW rows than corn in NS rows, but lack of replication makes it difficult to be certain that this was due to row direction. Green NDVI was less sensitive than reflectance to row direction and therefore may be more appropriate for use in a real-time variable-rate nitrogen application system.

Nitrogen response of no-till corn in first and second years following Conservation Reserve Program.

Reflectance measurements of crop plants and canopies show promise for guiding within-season, variable-rate nitrogen (N) application. Most research results have been obtained around solar noon with clear skies. However, for practical application, the system must work under cloudy skies or away from solar noon. The objective of this work was to assess the effect of cloud conditions on reflectance measurements of a corn canopy. The approach was to estimate an instantaneous sky clearness index (ICI) which could be used to correct field radiometer data for variations in cloud cover, such that the same reflectance reading would be obtained (and the same N recommendation made) for the same plants regardless of cloud conditions. Readings were taken from morning until night over 11 days with a range of sky conditions (sunny, overcast, partly cloudy). Data from clear days were used to estimate the theoretical expected spectral global radiation incident on a horizontal surface. The ICI was calculated as the ratio between the actual spectral global radiation and the corresponding theoretical global radiation. Analysis of the ICI for each band showed that the influence of cloudiness was different for each band. Thus, the cloud effect could not be compensated by the use of a band ratio or vegetation index.

Yield components of soybean plants infected with soybean cyst nematode and sprayed with foliar applications of boron and magnesium.

Abstract A considerable amount of land enrolled in the Conservation Reserve Program (CRP) has been and will be returned to row crop production. It is difficult to predict how to manage nitrogen (N) fertilizer for these row crops, since there are plausible reasons to expect either substantial N immobilization or substantial N mineralization due to the effects of CRP enrollment. Our objective was to characterize corn (Zea mays L.) yield response to N following CRP in order to develop N management recommendations. Corn was planted either directly into killed CRP sod (CRP‐corn) or following soybean [Glycine max (L.) Merr.] that had been planted into killed CRP sod (CRP‐SB‐corn)‐ We applied a range of N rates and determined the economically optimum N rate from the yield response data. In both years of the study, the optimum N rate for CRP‐corn was much higher (181 and 230 lb N acre‐1 in 1996 and 1997, respectively) than theoptimum N rate for CRP‐SB‐corn(108 and 113 lb Nacre‐1 in 1996 and 1997, respectively). CRP‐corn with no N fertilizer appeared extremely N deficient for the first half of the season. We observed a large flush of inorganic soil N in late summer of the first year out of CRP, but this N was apparently too late for optimum corn production that season. We recommend soybean as the first choice row crop to plant immediately following CRP. If corn is to be planted immediately following CRP, we recommend higher‐than‐normal N rates to optimize production.

Tillage Effects on Corn Response to Starter Fertilizer

Abstract Investigations into the effect of soybean cyst nematode (SCN, Heterodera glycines, Ichinoe) on the yield components of soybean [Glycine max (L.) Merr.] have shown that pod numbers are reduced with increasing SCN initial populations (Pi) present in the soil at planting. The main method by which SCN alters pod numbers is through reductions in the number of branches per plant. Foliar applications of boron (B) and B in combination with magnesium (Mg) (B+Mg) increase yield of soybean not infected with SCN by increasing pod number per plant, especially the number of pods on branches. The objective of this research was to determine if foliar applications of B and B+Mg ameliorates the effect of SCN by increasing yield on branches. Field experiments were conducted in 1993 and 1994 in 1 m2 microplots to compare foliar applied B and B+Mg to a control treatment. Foliar applications were made at four intervals spaced throughout soybean reproductive development of Pioneer brand 9391, an SCN susceptible cultivar. There were 12 levels of SCN Pi in 1993 and 11 levels in 1994. For each treatment, including control, grain yield was regressed on SCN Pi. Yield was reduced with increasing SCN Pi in both years, but the rate of decrease did not differ among treatments. In addition, ANOVA of yield components revealed no treatment effects on the number of branches per plant, the number of branch pods per plant, or the total number of pods per plant. Thus, foliar applications of B or B+Mg did not ameliorate the effects of SCN on soybean.