Search

Phosphorus (P) fertilizer recommendations based on the build and maintain (B&M) or the sufficiency philosophies were compared at six sites across Minnesota. Various levels of soil test P (STP) levels were established over four growing seasons. Applied P and P removed in harvested grain were monitored and used to develop a soil net P balance (Net P). Linear regression of net P with changes in STP was highly significant. Initial STP levels could be maintained at four of the six sites with a negative Net P. At those same sites, a zero Net P would tend to slowly increase STP over time. A sequential soil P fractionation analysis was conducted on soils from the six sites at the initiation and at the end of the 4‐year period. Nine total soil P fractions were extracted that represented both inorganic P (Pi) and organic P (Po) in the labile and non or less labile soil P pools. A positive linear relationship between Net P and changes in Pi fractions was significant. As Net P increased, so did the changes in Pi in the Resin, BiCarb, and NaOH fractions. These three fractions accounted for 66% to >100% of the changes in Net P with Resin and NaOH accounting for the majority of Net P. Changes in Net P that were accounted for in the less labile P pools, Sonic and HCl fractions, variable, and difficult to determine. There was little effect of Net P on Po fractions. Core ideas: Soil net P balance was positively correlated with changes in STP over four growing seasons.Medium STP interpretation class was maintained in most of these soils with a slight negative soil net P balance.In those same soils, a zero‐soil net P balance would tend to raise STP over time.Soil net P balance is positively related to changes in soil P, mostly in the labile and moderately labile fractions. [ABSTRACT FROM AUTHOR]

Potato (Solanum tuberosum L.) production on sandy soils requires added N. Only 40–60% of the applied N is acquired by the crop. Increased N use efficiency (NUE) and its components, N utilization efficiency (NUtE) and N uptake efficiency (NUpE), could reduce fertilizer rates and environmental losses. We compared N efficiency in fresh‐market red potato varieties, in terms of yield and quality traits, and examined potential mechanisms for that efficiency including uptake, utilization, and increased root growth. We grew selections from a red potato breeding population and commercial varieties under two N rates: 101 and 202 kg N ha−1. We compared NUE, NUpE, and NUtE in low and high N. We compared root phenotypes at tuber initiation and yield and skin quality metrics at harvest. Values for NUtE correlated with NUE and yield in low N and NUpE correlated with NUE and yield in high N. Low‐N conditions produced smaller tubers, while high N resulted primarily in medium tubers. Nitrogen did not affect skinning and redness but low N did result in slightly lighter skin color. Total root mass 45 d after planting (DAP) correlated with final yield and NUE but did not correlate with measures of N uptake across treatments. Larger roots correlated with NUpE only in the high‐N treatment. Selection under low N may reveal NUE and expose more stable representations of the genetic components of skin quality phenotypes. While skinning and skin color were more variable among varieties in low N, within variety they exhibited year‐to‐year consistency. [ABSTRACT FROM AUTHOR]

Anaerobic potentially mineralizable nitrogen (PMN) combined with preplant nitrate test (PPNT) or pre‐sidedress nitrate test (PSNT) may improve corn (Zea mays L.) N management. Forty‐nine corn N response studies were conducted across the U.S. Midwest to evaluate the capacity of PPNT and PSNT to predict grain yield, N uptake, and economic optimal N rate (EONR) when adjusted by soil sampling depth, soil texture, temperature, PMN, and initial NH4–N from PMN analysis. Pre‐plant soil samples were obtained for PPNT (0‐ to 30‐, 30‐ to 60‐, 60‐ to 90‐cm depths) and PMN (0‐ to 30‐cm depth) before corn planting and N fertilization. In‐season soil samples were obtained at the V5 corn development stage for PSNT (0‐ to 30‐, 30‐ to 60‐cm depths) at 0 kg N ha−1 at‐planting rate and for PMN when 0 and 180 kg N ha−1 was applied at planting. Grain yield, N uptake, and EONR were best predicted when separating soils by texture or sites by annual growing degree‐days and including PMN and initial NH4–N with either NO3–N test. Using PSNT (mean R2 =.30)‐instead of PPNT (mean R2 =.19)‐based models normally increased predictability of corn agronomic variables by a mean of 11%. Including PMN and initial NH4–N with PPNT or PSNT only marginally improved predictability of grain yield, N uptake, and EONR (R2 increase ≤.33; mean R2 =.35). Therefore, including PMN with PPNT or PSNT is not suggested as a tool to improve N fertilizer management in the U.S. Midwest. [ABSTRACT FROM AUTHOR]

The anaerobic potentially mineralizable N (PMN) test combined with the preplant (PPNT) and presidedress (PSNT) nitrate tests may improve corn (Zea mays L.) N fertilization predictions. Forty‐nine corn N response experiments (mostly corn following soybean [Glycine max (L.) Merr.]) were conducted in the U.S. Midwest from 2014–2016 to evaluate the ability of the PPNT and PSNT to predict corn relative yield (RY) and N fertilizer over‐ and under‐application rates when adjusted by PMN. Before planting and N fertilization, PPNT (0–30, 30–60, and 60–90 cm) and PMN (0–30 cm) samples were obtained. In‐season soil samples were obtained at the V5 development stage for PSNT (0–30, 30–60 cm) in all N rate treatments and PMN (0–30 cm) in only the 0 and 180 kg N ha−1 preplant N treatments. Increasing NO3–N sampling depths beyond 30 cm with or without PMN improved RY predictability marginally (R2 increase up to 0.20) and reduced over‐ and under‐application frequencies up to 14%. Including PMN (preplant only) with PPNT or PSNT improved RY predictability minimally (R2 increase up to 0.10) only for coarse‐ and medium‐textured soils, but N fertilizer over‐ and under‐application frequencies were not substantially reduced (≤12%). These marginal improvements in RY predictability and N fertilizer over‐ and under‐application frequencies, regardless of the variables used (e.g., fertilization, sampling depth, soil texture, and growing degree‐day categories), demonstrate that including PMN with soil NO3–N alone does not improve corn N fertilization need predictions enough to recommend their use. [ABSTRACT FROM AUTHOR]

Nitrogen (N) loss from cropping systems has important environmental implications, including contamination of drinking water with nitrate. A 2‐yr study evaluated the effects of six N rate, source, and timing treatments, including a variable rate (VR) N treatment based on the N sufficiency index approach using remote sensing, and two irrigation rate treatments, including conventional and reduced rate, on nitrate leaching, residual soil nitrate, and plant N uptake for potato (Solanum tuberosum L. cv. Russet Burbank) production in 2016 and 2017 on a Hubbard loamy sand. Nitrate leaching losses measured with suction‐cup lysimeters varied between 2016 and 2017 with flow‐weighted mean nitrate N concentrations of 5.6 and 12.8 mg N L−1, respectively, and increased from 7.1 to 10.4 mg N L−1 as N rate increased from 45 to 270 kg N ha−1. Despite reductions in N rate of 22 and 44 kg N ha−1 in 2016 and 2017, respectively, for the VR N treatment, there was no significant difference in nitrate leaching compared with the existing N best management practices (BMPs). Reducing irrigation rate by 15% decreased nitrate leaching load by 17% through a reduction in percolation. Residual soil nitrate N in the top 60 cm across all treatments (7.9 mg N kg−1) suggests a risk for nitrate leaching during the nongrowing season, and plant N uptake did not explain yearly variation in nitrate leaching and residual soil nitrate. Although existing N BMPs are effective at controlling N losses, development of alternative practices is needed to further reduce the risk of groundwater contamination. [ABSTRACT FROM AUTHOR]

Understanding the variables that affect the anaerobic potentially mineralizable N (PMNan) test should lead to a standard procedure of sample collection and incubation length, improving PMNan as a tool in corn (Zea mays L.) N management. We evaluated the effect of soil sample timing (preplant and V5 corn development stage [V5]), N fertilization (0 and 180 kg ha−1) and incubation length (7, 14, and 28 d) on PMNan (0–30 cm) across a range of soil properties and weather conditions. Soil sample timing, N fertilization, and incubation length affected PMNan differently based on soil and weather conditions. Preplant vs. V5 PMNan tended to be greater at sites that received < 183 mm of precipitation or < 359 growing degree-days (GDD) between preplant and V5, or had soil C/N ratios > 9.7:1; otherwise, V5 PMNan tended to be greater than preplant PMNan. The PMNan tended to be greater in unfertilized vs. fertilized soil in sites with clay content > 9.5%, total C < 24.2 g kg−1, soil organic matter (SOM) < 3.9 g kg−1, or C to N ratios < 11.0:1; otherwise, PMNan tended to be greater in fertilized vs. unfertilized soil. Longer incubation lengths increased PMNan at all sites regardless of sampling methods. Since PMNan is sensitive to many factors (sample timing, N fertilization, incubation length, soil properties, and weather conditions), it is important to follow a consistent protocol to compare PMNan among sites and potentially use PMNan to improve corn N management. [ABSTRACT FROM AUTHOR]

Estimates of mineralizable N with the anaerobic potentially mineralizable N (PMNan) test could improve predictions of corn (Zea mays L.) economic optimal N rate (EONR). A study across eight US midwestern states was conducted to quantify the predictability of EONR for single and split N applications by PMNan. Treatment factors included different soil sample timings (pre-plant and V5 development stage), planting N rates (0 and 180 kg N ha-1), and incubation lengths (7, 14, and 28 d) with and without initial soil NH4--N included with PMNan. Soil was sampled (0-30 cm depth) before planting and N application and at V5 where 0 or 180 kg N ha-1 were applied at planting. Evaluating across all soils, PMNan was a weak predictor of EONR (R² ≤ 0.08; RMSE, ≥67 kg N ha-1), but the predictability improved (15%) when soils were grouped by texture. Using PMNan and initial soil NH4--N as separate explanatory variables improved EONR predictability (11-20%) in fine-textured soils only. Delaying PMNan sampling from pre-plant to V5 regardless of N fertilization improved EONR predictability by 25% in only coarse-textured soils. Increasing PMNan incubations beyond 7 d modestly improved EONR predictability (R² increased ≤0.18, and RMSE was reduced ≤7 kg N ha-1). Alone, PMNan predicts EONR poorly, and the improvements from partitioning soils by texture and including initial soil NH4--N were relatively low (R² ≤ 0.33; RMSE ≥ 68 kg N ha-1) compared with other tools for N fertilizer recommendations. [ABSTRACT FROM AUTHOR]

Availability of soil moisture and N are primary limiting factors for potato growth on sandy soils in humid climates. This study was conducted to determine whether tuber yield or net economic return were affected by variable rate (VR) N or reduced irrigation management, and to evaluate methods to detect crop N status including remote sensing, chlorophyll meter, and petiole sampling. The effects of six N rate, source, and timing treatments and two irrigation rate treatments on tuber yield, quality, and net profitability for potato [Solanum tuberosum (L.) 'Russet Burbank'] were investigated in 2016 and 2017 at Becker, MN, on a Hubbard loamy sand. A VR N treatment based on the N sufficiency index (NSI) approach using remote sensing was also tested. Irrigation treatments included a conventional rate (100%) and a reduced rate (85%). The VR treatment reduced N applied relative to the recommended rate by 22 and 44 kg N ha-1 in 2016 and 2017, respectively. Irrigation rate was reduced by 29 and 33 mm in 2016 and 2017, respectively. Neither VR N nor reduced irrigation produced significant differences in tuber yield or net return compared to full rate treatments. Using NSI, remote sensing was able to predict crop N status with comparable accuracy to petiole sampling while chlorophyll meter measurements were less sensitive to detecting crop N stress. Managing N using remote sensing and reducing irrigation rate are strategies that could be used on sandy soils in humid climates without having agronomic or economic impacts on potato production. [ABSTRACT FROM AUTHOR]

Sulfur is applied to irrigated corn (Zea mays L.) grown on sandy soils. The objective of this study was to evaluate the sprinkler-irrigated corn response to S. Treatments were a factorial combination of 0, 14, 28, and 42 kg S ha-1 as (NH4)2SO4 applied on the soil surface at four locations at planting and in season (V5). Tissue samples were collected at V8 and R2 and evaluated along with corn grain yield and soil pore water SO4 2--S concentration measured at 60 cm with suction tube lysimeters. Application of S increased V8 plant mass, V8 whole plant S concentration and S uptake, and R2 leaf S concentration but did not increase corn grain yield. Decreased V8 plant mass was a result of S deficiency and was only corrected when some S was applied at planting. A total of 28 kg S ha-1 was sufficient to ensure adequate plant growth and S uptake whether S was applied at planting, in-season, or as a combination of the two timings. Concentrations of S were elevated in soil pore water from at planting and in-season S application indicating a portion of the S applied were still available for most'and at the end of'the growing season. Sulfur fertilizer is crucial early in the growing season for irrigated corn to ensure optimal corn growth. Rate of application is more important than time of S application in irrigated corn production. Incidental applications of S may reduce the need of S fertilizer for irrigated corn.

Nitrogen provided to crops through mineralization is an important factor in N management guidelines. Understanding of the interactive effects of soil and weather conditions on N mineralization needs to be improved. Relationships between anaerobic potentially mineralizable N (PMNan) and soil and weather conditions were evaluated under the contrasting climates of eight US Midwestern states. Soil was sampled (0.30 cm) for PMNan analysis before pre-plant N application (PP0N) and at the V5 development stage from the pre-plant 0 (V50N) and 180 kg N ha-1 (V5180N) rates and incubated for 7, 14, and 28 d. Even distribution of precipitation and warmer temperatures before soil sampling and greater soil organic matter (SOM) increased PMNan. Soil properties, including total C, SOM, and total N, had the strongest relationships with PMNan (R2 < 0.40), followed by temperature (R2 < 0.20) and precipitation (R2 < 0.18) variables. The strength of the relationships between soil properties and PMNan from PP0N, V50N, and V5180N varied by .10%. Including soil and weather in the model greatly increased PMNan predictability (R2 < 0.69), demonstrating the interactive effect of soil and weather on N mineralization at different times during the growing season regardless of N fertilization. Delayed soil sampling (V50N) and sampling after fertilization (V5180N) reduced PMNan predictability. However, longer PMNan incubations improved PMNan predictability from both V5 soil samplings closer to the PMNan predictability from PP0N, indicating the potential of PMNan from longer incubations to provide improved estimates of N mineralization when N fertilizer is applied.

Acrylamide is a potentially harmful compound when consumed in the human diet and is formed during potato (Solanum tuberosum L.) processing from the precursors reducing sugars and asparagine. The objective of this study was to determine the effects of N rate (135-404 kg ha-1) on tuber yield and quality and tuber reducing sugars and asparagine concentrations in newly released cultivars Easton and Dakota Russet, relative to the standard cultivar Russet Burbank. Tuber samples were collected at intervals from initial set through harvest during two growing seasons. Tuber yield of all cultivars increased quadratically with increasing N rate. Highest yield was produced by Easton, followed by Russet Burbank and Dakota Russet. Russet Burbank had more tubers per plant than the new cultivars. Specific gravity decreased with increasing N rate and was lowest in Russet Burbank both years. The new cultivars had a lower hollow heart incidence than Russet Burbank when environmental conditions were favorable for hollow heart development. Tuber-reducing sugars changed during the growing season but were related more to cultivar and growing conditions than N rate. New cultivars had lower reducing sugars than Russet Burbank. In contrast to reducing sugars, asparagine increased with increasing N rate and was less affected by environmental conditions during the growing season. Easton had slightly lower asparagine concentrations than Russet Burbank and Dakota Russet. This study indicates that cultivar and growing conditions have a dominant effect on tuber-reducing sugars, while N rate has a more consistent effect on tuber asparagine. [ABSTRACT FROM AUTHOR]

A suitable N source and an optimal application rate can improve the N-use efficiency of potato (Solanum tuberosum L.) while minimizing N losses, especially when potato is grown in sandy soils. Three experiments were conducted at irrigated sandy soil sites in São Paulo State, Brazil, to evaluate the effects of ammonium sulfate (AMS), ammonium sulfate nitrate with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (ASN+DMPP), and urea applied at three N rates (80, 120, and 160 kg ha-1), as well as a zero-N control on potato (cv. Agata). Leaf N and S concentrations, tuber yield, and agronomic efficiency (AE) were measured. The 80 kg N ha-1 rate was applied in the furrow at planting, and the other rates were split-applied, with 40 kg N ha-1 in the furrow at planting and the remainder applied at hilling. Regardless of the N source, the N fertilizer rates increased the potato leaf N concentration and tuber bulking of the potato crop, which in turn increased the tuber yield up to rates between 136 kg N ha-1 and at least 160 kg N ha-1. Among the N sources, ASN+DMPP fertilizer resulted in a higher potato tuber set and yield than urea and led to the highest AE compared to AMS and urea. Overall, these results suggest the potential for ASN+DMPP to improve the synchronization between soil N availability and potato N demand and provide a more appropriate balance of N forms in the soil when potato is cultivated in sandy soils in a tropical climate. [ABSTRACT FROM AUTHOR]

Specific gravity (SpGr) is often used to measure the processing quality of potato (Solanum tuberosum L.) tubers for French fries or potato chips because of its strong correlation with dry matter content and ease of measurement. For French fry processing genotypes, the desirable range for mean SpGr is typically 1.080 to 1.095, and a small variance around the mean is essential for product uniformity. Two multi-year, multi-location trials were conducted to investigate the genetics of SpGr in elite russet germplasm. Consistent with earlier studies, the mean SpGr was measured with high repeatability within each environment: the median plot-basis value was 0.83 for a national trial with six locations and 3 yr. In contrast, the median repeatability of the SD between tubers was only 0.21. Thus, multi-environment trials are needed to identify genotypes with a narrow SpGr distribution. Finlay--Wilkinson stability analysis of the mean SpGr established one genotype as an outlier: when best linear unbiased predictions were regressed on the environment means, this genotype had a regression coefficient of 2.1, compared with 0.4 to 1.4 for the others. The genetic correlation between environments showed a consistent regional pattern in mean SpGr over the years. There was a higher mean correlation between environments within the Pacific Northwest (0.97), Upper Midwest (0.91), and Northeast (0.85) than between environments from the different regions (0.35-0.78). Although breeding for national adaptation is an attractive idea, our results suggest that genetic gain may be easier to achieve at the regional level. [ABSTRACT FROM AUTHOR]

Characterizing corn (Zea mays L.) grain yield (GY) response to N is critical for maximizing profits, increasing N use efficiency and minimizing environmental impacts. Although a large database of GY response to N exists for highly productive soils, few data exist for less productive soils. While changes in precipitation are expected in the future, few studies have compared GY response to varying N management practices under conditions of varying water availability. We measured GY and basal stalk nitrate nitrogen (BSN) at harvest using split-applied urea at eight N rates under fully-irrigated (FI) and water-stressed (WS) conditions in a loamy sand over 2 yr (2009 and 2010). We also measured GY and BSN using single, pre-plant applications of urea, polymer-coated urea (PCU) and urea amended with urease and nitrification inhibitors (IU) at one or two N rates. The results showed that economic optimum nitrogen rate (EONR) and agronomic optimum nitrogen rate (AONR) did not vary by water management, in spite of signifi cant increases in GY (up to 48%) under FI compared to WS. Modifi cation of N fertilizer timing or N source was effective for increasing GY (by 18-41%) with FI, but did not affect GY under WS conditions. Averaged across years, BSN was greater with WS compared to FI at most N rates; however, BSN corresponding to AONR was within the optimal range for both water regimes. These findings may have important implications in areas where changes in irrigation practices or water availability are expected under future climate conditions. [ABSTRACT FROM AUTHOR]

Polymer-coated ureas (PCUs) can reduce N leaching in potato (Solanum tuberosum L.) production while maintaining yields. However, damage to the polymer coating during handling increases N release and potentially affects leaching and crop response. A 2-yr study was conducted to develop a quick test of PCU damage, compare its results with N release under field conditions, and determine damage effects on N uptake and yield in field experiments. A 24-h water immersion procedure was developed to measure N release differences from two sources of the PCU fertilizer Environmentally Smart Nitrogen (ESN) handled in different ways: ESN(C), dealer grade undamaged control, and ESN(A), damaged by air boom spreader application. Nitrogen release from ESN(A) was more rapid in both the 24-h test and during in situ soil incubation. Quick test results were positively correlated with N release during the first 7 d of field incubation (R² = 0.91, adjusted R² = 0.86). Differences in prill damage between ESN(C) and ESN(A) were greater in 2010 than 2011. Limited crop response differences occurred in 2011, but in 2010 petiole nitrate-N was more stable and higher late in the season for ESN(C) than ESN(A), and tuber, vine, and total N uptake were significantly greater for ESN(C). Tuber yield and size were not significantly affected by ESN damage. Based on these results, the quick test provides an accurate assessment of potential differences in N release during the growing season due to coating damage and can be used to evaluate leaching potential and possible need for fertigation. [ABSTRACT FROM AUTHOR]