W. P. Piekielek

Using a chlorophyll meter to predict nitrogen fertilizer needs of winter wheat

Abstract Although it has been shown that the nitrogen (N) concentration of winter wheat (Triticum aestivum L. em Thell) at Feekes growth stage 5 (GS 5) can be used to assist in making more accurate spring N fertilizer recommendations, the need remains to find a more convenient and accurate means for predicting N fertilizer needs of wheat. We conducted seven N fertilizer response experiments over two years in central and southeastern Pennsylvania to determine if chlorophyll meter readings of wheat leaves at GS 5 could predict whether a significant, positive grain yield response to N fertilizer would be obtained. The chlorophyll meter readings at GS 5 were more accurate (correctly predicting response to N fertilizer in 24 of 25 treatments for a 4% error rate) than GS 5 plant N concentration (20% error rate). There were too few treatments with a positive response to N fertilizer to be able to determine if chlorophyll meter readings could be used to accurately predict N fertilizer rates needed for economic o...

Field evaluation of several chemical indexes of soil nitrogen availability.

The ability of several chemical soil N availability indexes to predict the N supplying capability (NSC) of soils to maize in the field was evaluated in 49 field experiments over 3 years in Pennsylvania. Two recently proposed indexes based on the amount of NH4+ released by treating soil with 2 M KCl at 100°C for 4 hr or with a pH 11.2 phosphate-borate buffer for 8 min were not good predictors of NSC (r=0.484 and 0.254, respectively). The absorbance of a 0.01 M NaHCO3 extract at 260 nm was also poorly correlated with field-measured NSC (r=0.412). The pre-sidedress soil NO3− test (PSNT), the soil NO3− concertration in the surface 20 cm of soil at planting, and the UV absorbance at 200 nm of a 0.01 M NaHCO3 extract of at planting soils were all moderately well correlated with NSC (r=0.672, 0.750, and 0.737, respectively). The latter two indexes are very simple, rapid, and inexpensive to perform and offer the possibility of improving the prediction of NSC in heavily manured fields.

Diurnal, shade, and hybrid effects on nitrate content of young corn stalks

Abstract Significant correlations have been found between the nitrate concentration in young corn (Zea mays L.) stalks and available soi 1 N and relative grain yield when N availability is a yield limiting factor. To successfully use nitrate tissue testing as an indicator of the N status of plants, the effects of factors other than soil or fertilizer N on the nitrate concentration in the tested tissue must be understood. Diurnal effects on stalk nitrate content were studied in a greenhouse experiment, in which stalk samples were collected every two hours for 24 hours, and in a field study, where plants in an N‐fertilizer response experiment were sampled at sunrise and at mid‐day. A significant diurnal cycle was observed for stalk nitrate content in the greenhouse, with a peak at 0800 h and a low at 1400 h, but no diurnal effect was found in the field study, possibly due to plant stress from other environmental factors. In a second greenhouse study, stalk samples from seedlings in direct and 66% shaded nat...

Development of a quicktest kit method to measure soil nitrate

Abstract A soil nitrate test taken about 4 weeks after emergence has been proposed to predict the corn (Zea mays L.) yield reponse to sidedress N fertilizer applications. Use of this test would be increased if the soil analysis and interpretation could be done rapidly, since the fertilizer must be applied within one to two weeks after sampling. Because of this time constraint, mailing samples to a centralized laboratory is unattractive to many farmers. One potential solution to this problem would be to have the analysis done locally using a quicktest kit. A proposed method for analyzing soil samples for nitrate was adapted for use under field conditions. The method is based on the analysis of soil extracts using nitrate sensitive test strips and a hand held reflectometer. Two soil measuring methods, a conventional scooping method and a weighing procedure using an inexpensive balance, were evaluated for inclusion in the test kit. Evaluation was based on the ability of the methods to measure 20 g of soil. F...

Soil magnesium level, corn (Zea mays L.) yield, and magnesium uptake

Abstract The exchangeable soil Mg level recommended for agronomic crop production by different soil testing services ranges from 25 to over 180 ppm (?10% saturation of the cation exchange capacity). In some cases the justification for high soil Mg recommendations is to ensure that forage Mg concentrations are high enough to prevent hypomagnesemia in ruminants consuming it. There has been very little research on determining the minimum amount of soil Mg needed to produce optimum corn (Zea mays L.) grain yields. Some soil testing services recommend adding Ca to soils having high exchangeable Mg contents in spite of little published evidence to support the efficacy of this practice. In 1980, field experiments were initiated on two low and one high exchangeable Mg soils in Pennsylvania to determine: 1) the high and low critical soil Mg levels for corn grain production, 2) how well several soil test methods for determining Mg availability predicted Mg uptake by corn, and 3) the exchangeable soil Mg levels need...

Chemical characterization of two extracts used in the determination of available soil nitrogen

SummaryTwo soil extracts used for chemical indexes for N availability, 0.01M NaHCO3 and boiling 0.01M CaCl2, were analyzed in effort to learn more about the nature of the extracted organic matter (O.M.). The two extracts appeared to remove different fractions of the soil O.M. A study of five soils showed that the C/N value of the NaHCO3 extract (following decarbonation) was significantly higher than that of the total soil O.M.; while the C/N value in the boiling CaCl2 extract was not significantly different from that in the soil O.M. There was also significant variation in C/N values among soils for the boiling CaCl2 extract. The extracts of three soils were analyzed for apparent molecular weight distribution using gel filtration and the results compared to those for base-extracted humic substances. Almost all the molecules in the extracts had apparent molecular weights less than 21,000 daltons while 21 to 47% of the humic substances from the same soils (extracted with 0.5M NaOH) had molecular weights greater than 21,000 daltons. In the boiling CaCl2 extract, 78 to 87% of the humic substances had apparent molecular weights less than 1,000 daltons, whereas with the NaHCO3 extract, 42 to 83% of the humic substances were in the 1,000 to 21,000 dalton range. Forty-three to 92% of the N extracted by the NaHCO3 was in protein form, and 8 to 30% was ninhydrin-detectable. In the boiling CaCl2 extract 25 to 30% of the extracted N was ninhydrin-detectable. For the same 10 soils, ninhydrin-detectable N values of the boiling CaCl2 extract appeared closely related to greenhouse and field relative N uptake, while the ninhydrin-detectable N values of the NaHCO3 extract appeared unrelated to both. The protein N and protein in plus ninhydrin-detectable N values of the NaHCO3 extract were closely related to greenhouse relative N uptake only. The results of this study indicated that specific fractions of the soil O.M. were being extracted by the two solutions and that significant differences existed in the chemical nature of the two extracts.

A comparison of laboratory, greenhouse, and field indicators of nitrogen availability

Abstract In the past, greenhouse and field results have been used individually to test the predictive capacity of laboratory indexes of soil nitrogen availability. The field results are the most reliable measure of field available N, but greenhouse experiments can be conducted more easily and over the whole year. A comparison of the laboratory, greenhouse and field indicators of N availability was therefore needed to determine if greenhouse data could be substituted for field results in this capacity. In a study of ten Pennsylvania soils there was no significant correlation between field relative N uptake and greenhouse relative N uptake which suggested that greenhouse results could not be substituted for field results in testing the reliability of laboratory indexes. There was no significant correlation between the field results and the five laboratory indexes tested (total N, total organic matter, Fox‐Piekielek Test, MacLean Test, and Keeney‐Bremner Test). However, the latter three tests did correlate w...

Yield response to N fertilizer and N fertilizer use efficiency in no‐tillage and plow‐tillage corn 1

Abstract Yield, and N uptake response to several rates of ? fertilizer applied to non‐tilled (NT) and plow‐tilled (PT) corn were compared for 3 years in an experiment conducted on Hagerstown silt loam (Typic hapludult, fine‐loamy, mixed, mesic) in central Pennsylvania. Insufficient moisture limited yields two of the three years of the study. The 3‐year average grain yields were significantly lower with NT than with PT at the 0 kg/ha broadcast N rate and higher with NT than PT at the upper two rates (150 and 200 kg broadcast N/ha). In the year when moisture did not limit yield potential, yields with NT were lower than with PT at the 0 kg/ha broadcast ? rate, but maximum yields were equal with both tillages. It was speculated that the greater maximum yields with NT in the drier years were due to the greater soil moisture availability with NT. Analysis of the 3‐year average quadratic‐linear plateau yield response to ? fertilizer rate functions for the two tillage systems indicated that the economic optimum ?...

Effect of harvest method and feed value on the economic optimum nitrogen rate for corn

Abstract Consideration of the harvest method and protein content of corn grain and forage may be important variables for estimating Economic Optimum Nitrogen (N) (EON) rates for corn. Corn grain yield, forage yield, grain protein and forage protein data from twenty five N response experiments conducted in Pennsylvania were analyzed to determine the effect of harvest method and a price adjustment based on grain and forage protein content on the EON rate. The value of the protein in this study was assumed to be that of substituting soybean meal in the ration for growing beef cattle or dairy cattle. There was no difference in the EON for corn harvested for grain compared to corn harvested for forage when the protein content was not considered. When price adjustments were made for the protein content of the grain and forage, the EON rates increased 10 kg/ha for grain and 22 kg/ha for forage. With the protein price adjustments, the EON was 14 kg/ha higher for forage than grain. These results support the recomm...