Brenda Tubana

Adjusting Midseason Nitrogen Rate Using a Sensor-Based Optimization Algorithm to Increase Use Efficiency in Corn

ABSTRACT This study was conducted to formulate an in-season nitrogen (N) fertilization optimization algorithm (NFOA) to estimate midseason N rates that maximize corn (Zea mays L.) growth and minimize fertilizer inputs. Treatments included: a zero kg N ha−1; three treatments of 134 kg N ha−1 fixed rate applied in split, preplant, or sidedress; two treatments of 67 kg N ha−1 fixed rate preplant or sidedress applied; three NFOA-based midseason N rates (RI-NFOA, RICV-NFOA, flat-RICV-NFOA) with (67 kg N ha−1) and without preplant N; and two resolutions (0.34 and 2.32 m2) tested for RICV-NFOA only. With the 67 kg N ha−1 preplant application, midseason RI-NFOA-based N rates resulted in an N use efficiency (NUE) of 65% while the 134 kg N ha−1 fixed rate split applied had 56% NUE. Using the RICV-NFOA, NUE and net returns to N fertilizer were higher when spatial variability was treated at 2.32 m2 resolution.

Estimating sugarcane yield potential using an in-season determination of normalized difference vegetative index.

Estimating crop yield using remote sensing techniques has proven to be successful. However, sugarcane possesses unique characteristics; such as, a multi-year cropping cycle and plant height-limiting for midseason fertilizer application timing. Our study objective was to determine if sugarcane yield potential could be estimated using an in-season estimation of normalized difference vegetative index (NDVI). Sensor readings were taken using the GreenSeeker® handheld sensor from 2008 to 2011 in St. Gabriel and Jeanerette, LA, USA. In-season estimates of yield (INSEY) values were calculated by dividing NDVI by thermal variables. Optimum timing for estimating sugarcane yield was between 601–750 GDD. In-season estimated yield values improved the yield potential (YP) model compared to using NDVI. Generally, INSEY value showed a positive exponential relationship with yield (r2 values 0.48 and 0.42 for cane tonnage and sugar yield, respectively). When models were separated based on canopy structure there was an increase the strength of the relationship for the erectophile varieties (r2 0.53 and 0.47 for cane tonnage and sugar yield, respectively); however, the model for planophile varieties weakened slightly. Results of this study indicate using an INSEY value for predicting sugarcane yield shows potential of being a valuable management tool for sugarcane producers in Louisiana.

Mid-season prediction of wheat-grain yield potential using plant, soil, and sensor measurements

ABSTRACT The components that define cereal-grain yield potential have not been well defined. The objective of this study was to collect many differing biological measurements from a long-term winter wheat (Triticum aestivum L.) study in an attempt to better define yield potential. Four treatments were sampled that annually received 0, 45, 90, and 135 kg N ha−1 at fixed rates of phosphorus (P) (30 kg ha−1) and potassium (K) (37 kg ha−1). Mid-season measurements of leaf color, chlorophyll, normalized difference vegetative index (NDVI), plant height, canopy temperature, tiller density, plant density, soil moisture, soil NH4-N, NO3-N, organic carbon (C), total nitrogen (N), pH, and N mineralization potential were collected. In addition, soil texture and bulk density were determined to characterize each plot. Correlations and multiple linear-regression analyses were used to determine those variables that can predict final winter wheat grain yield. Both the correlation and regression analyses suggested mid-season NDVI, chlorophyll content, plant height, and total N uptake to be good predictors of final winter wheat grain yield.

A Review of Silicon in Soils and Plants and Its Role in US Agriculture: History and Future Perspectives

Abstract Silicon (Si) is the second most abundant element in the earth’s crust and plays a number of important roles in the mineral nutrition of plants. In the past 20 years, the scientific documentation on the benefits of Si to crops has helped establish Si fertilization as an agronomic practice in many agricultural lands worldwide. However, very little information has been consolidated on the use of Si specifically for US agriculture. Consequently, the objectives of this review are to provide (1) information on the dynamics of Si in soil, use, and sources; (2) a history and up-to-date documentation on Si-related research in many areas of US production agriculture; and (3) perspectives on Si as a plant beneficial nutrient and the potential of Si fertilization as an agronomic practice in US crop production systems. The Si-driven mechanisms enhancing the productivity of a wide array of crops under stressed conditions are discussed in this review. Based on the recent 10-year average production level and published shoot Si content, the principal crops grown in the United States can collectively take up 9.55 million tons of Si annually, whereas the annual Si removal rate for the entire US cropland area is estimated at 21.1 million tons. On the basis of this projected annual Si removal rate, adoption of continuous intensive farming systems in the country, low solubility of soil Si, and complex chemical dynamics of Si in soil, increasing plant-available Si levels through fertilization is therefore foreseen a logical agronomic practice for US agriculture.

NITROGEN ACCUMULATION IN SHOOTS AS A FUNCTION OF GROWTH STAGE OF CORN AND WINTER WHEAT

Midseason fertilizer nitrogen (N) rates based on predicted yields can be projected if the quantity of N accumulated in winter wheat (Triticum aestivum L.) and corn (Zea mays L.) is known especially early in the growing season. This study was conducted in 2006 and 2007 to establish the amount of N accumulated in corn and winter wheat over the entire growing season. Plots representing three N fertilization rates 0, 45, and 90 kg ha−1 at Stillwater and 0, 67, and 112 kg ha−1 at Lahoma were selected from two long-term wheat experiments located at research stations in Stillwater and Lahoma, Oklahoma. For corn, three N fertilization rates 0, 112 and 224 kg ha−1 at Lake Carl Blackwell and 0, 56 and 112 kg ha−1 at Perkins were selected from N studies, located at research stations near Lake Carl Blackwell and Perkins, Oklahoma. Sequential aboveground biomass samples were collected from 1 m2 area of wheat and 1.5 m long row (0.76 cm spacing) for corn throughout their respective growing seasons. In general, this work showed that more than 45% of the maximum total N accumulated could be found in corn plants by growth stage V8 (8th leaf collar fully unfolded). For winter wheat, more than 61% of the maximum total N accumulated at later stages of growth could be accounted for by Feekes growth stage 5 (F5, leaf strongly erected). Our findings are consistent with those of others showing that yield potential can be predicted at mid-season since such a large percentage of the total N accumulated was accounted for early on in the growing cycle of either wheat or corn.

Analysis of yield variability in winter wheat due to temporal variability, and nitrogen and phosphorus fertilization

Abstract Field average based recommendations have been a common practice for recommending the major crop nutrients nitrogen (N) and phosphorus (P). The problem is yield will not be the same from year to year with application of the same amount of recommended rate of fertilizer. The objectives of this study were to demonstrate how recommendations generated using nutrient response experiments were dynamic; and to assess the relative contribution of temporal variability, N and P fertilizers on winter wheat grain yield and N concentration. Twelve factorial combinations of four N (0, 56, 112, and 168 kg ha−1) and three P (0, 14.5, and 29 kg P ha−1) rates were evaluated in a randomized complete block design with three replications at Perkins, Oklahoma. To address the first objective, ANOVA and orthogonal polynomial contrasts were used. To address the second objective, a ten predictor variable multiple linear regression model with two quantitative variables and their interaction (N, P and N×P) and seven-year variables was evaluated and a reduced model containing seven variables was generated. Wheat grain yield showed three distinct responses to N rates: Linear, quadratic and no response. These individual year data show that it is not always appropriate to use results of nutrient response experiments to estimate next years N fertilizer requirement due to apparent temporal variability in the results. Wheat only responded to P during the first two years of the study. The reduced model from the regression analysis revealed that most of the variability in grain yield was accounted for by five individual indicator years and N only. High variability across years in grain yield and fertilizer (N and P) response, even between years of similar grain yield, is an indication of a given seasons production dependence on factors other than N and P.

In-season estimation of grain sorghum yield potential using a hand-held optical sensor

Abstract Sensor based nitrogen (N) management technology has helped to improve fertilizer recommendations for various crops. The objective of this study was to estimate the in-season yield potential (YP0) of grain sorghum (Sorghum bicolor L. Moench) using a hand held optical sensor. This experiment was conducted with four levels of N (50, 100, 150 and 200 kg ha−1) and three application timing (Preplant, topdress and split) arranged in a randomized complete block design with three replications at three locations, in Oklahoma in 2004 and 2005. Sensor readings were taken using red (650 ± 10 nm) and green (550 ± 12.5 nm) sensors at sorghum growth stages 2, 3, 5, 6 and 7. Results from statistical analysis have shown that 75 and 77% of the variation in sorghum grain yield was explained by red and green Normalized Difference Vegetation Index (NDVI), respectively at growth stage 3. Similarly, grain N content was correlated to both green and red (coefficient of determination, r2 = 0.61) NDVI readings at growth stage 3. In-season estimated yield (INSEY) derived from green NDVI was also found correlated with final grain yield (r2 = 0.71). The results of this experiment suggest that INSEY can be used as a tool to predict mid-season sorghum grain yield potential at sorghum growth stage 3.

Relationship between Nitrogen Use Efficiency and Response Index in Winter Wheat

ABSTRACT Although nitrogen use efficiency (NUE) of small grains is well documented at 33% worldwide, there has been little research relating NUE to yield factors. This study examined the relationship between NUE and the response index at harvest (RIHARVEST) of winter wheat (Triticum aestivum L.). Yield data from a long-term fertility study established at Lahoma, Oklahoma in 1971 was used to explore the relationship. In this report, six nitrogen (N) rates at non-limiting levels of P and K were evaluated. Regression analysis showed a positive relationship between NUE and RIHARVEST for all years across all N rates (r2 = 0.37). But this relationship was improved (r2 = 0.45) when both RINDVI and RIHARVEST were included in the model. The linear relationship between NUE and RIHARVEST was significantly improved, when yield data and corresponding NUE were separated according to the annually applied fixed N rate. As the N rate increased the resulting slope of the relationship between NUE and RI was reduced. These analyses also demonstrate that temporal variability in NUE exists and that NUE can be predicted.

Effect of Treating Field Spatial Variability in Winter Wheat at Different Resolutions

ABSTRACT This study was conducted to determine the scale at which spatial variability should be treated using an in-season nitrogen fertilization optimization algorithm (NFOA). Treatments included variable nitrogen (N) rate applications at three resolutions (0.84, 13.4, and 26.8 m2), two treatments of 90 kg N ha−1 fixed rate applied preplant or midseason, and a check plot. Treatments were arranged in a completely randomized design with three replications established at two locations for three years. On average, the NFOA-based N rates achieved a higher N use efficiency (NUE) of 41% compared with only 33% of the 90 kg N ha−1 fixed rate applied midseason. The highest NUE among the NFOA-based N rate treatments was 56% at 13.4 m2 resolution. These benefits were attributed to a large reduction in NFOA-based N rate recommendations. Determining midseason N rate requirements using NFOA at 13.4 m2 resolution resulted in increased NUE and net return to N fertilizer.

Long-Term Effects of Nitrogen Management Practices on Grain Yield, Nitrogen Uptake, and Efficiency in Irrigated Corn

ABSTRACT Crop management strategies that improve Nitrogen Use Efficiency (NUE) increase profits while reducing the detrimental effects on the environment associated with fertilizer nitrogen (N) loss. Effective N management should include several critical factors that are very interrelated. A study was conducted at the Panhandle Research and Extension Center, Goodwell, OK to evaluate the effects of multiple nitrogen management practices including N rate, source, time of application, methods of fertilizer and residue incorporation over a long period of time on grain yield, N uptake and NUE in irrigated corn. Fourteen treatments were evaluated in a randomized complete block design with three replicates. Results of data analyzed on the individual year and averages of all years showed that grain yield and N uptake were improved with N rates and N management practices compared to checks. Both N recovery and efficiency of use were high for the 118 kg N ha− 1 rate.