Surface liming will prevent the formation of an 'acid roof' on the surface of soil cropped in no-till corn (Zea mays L.). A study was begun in 1985 to determine the effectiveness of unincorporated liming in raising pH in no-till soil which had developed significant acidity throughout the upper 15 cm. Lime was applied at 0, 3.36, 6.72 and 10.08 Mg ha-1. All lime was applied on 26 April 1985 and was not incorporated. The pre-liming pH at 0-5 cm below the surface was 4.5; after two months the pH was raised to 5.6, 5.8, and 6.0 by 3.36, 6.72 and 10.08 Mg ha-1 of lime, respectively. After 19 months soil-pH was raised to 6.0, 6.4 and 6.6 by liming at 3.36, 6.72 and 10.08 Mg ha-1 respectively. Soil-pH below 5 cm was not affected by any rate of lime during the first 19 months after liming. Tissue analysis of corn ear leaves indicated that calcium uptake was increased significantly by lime in 1985, while manganese uptake was significantly reduced. In 1986, increases in calcium were greater than in 1985 and additional significant reduction in manganese uptake was accompanied by significantly reduced zinc and copper uptake. In both 1985 and 1986, a trend toward lower average corn grain yield in unlimed plots than in limed plots was noted, but the yield increases due to lime were not statistically significant in either year. This study will be continued as a long term investigation of lime penetration into no-till soil and response of corn to soil-pH changes.
Because of both economic and environmental concerns, soil testing is becoming an increasingly important component of crop-production systems. This increasing demand for soil testing will necessitate more efficient methods for routine soil testing. The Mehlich-3 soil test has been proposed as an extractant that can be used for simultaneous extraction of several nutrients including both P and K. Before this extractant can be used in place of the current extractants, it must be evaluated in field calibration studies. This study was designed to compare the ability of the Mehlich-3 extractant to predict corn (Zea mays L.) yield response to P and K with the Bray-Kurtz P1 extractant for P and the neutral, 1N ammonium acetate extractant for K. A field study was conducted at 67 locations across Pennsylvania over 4 yr. A factorial arrangement of P (0 and 88 kg ha-1) and K (0 and 168 kg ha-1) was applied at each location. Corn-grain yield was measured as the response parameter. The Mehlich-3 extractant was highly correlated with the Bray-Kurtz P1 extractant (r=0.99) and neutral, 1N ammonium acetate K extractant (r=0.96). The calibrations for the Mehlich-3 P and Bray-Kurtz P1 were similar. While there was a large amount of scatter in both data sets, a Cate-Nelson partitioning of the data resulted in critical levels of 43 and 45 kg P ha-1 for the Bray-Kurtz P1 and Mehlich-3 P extractants, respectively. The calibrations for the Mehlich 3 and the neutral, 1N ammonium acetate extractants were also similar. Again, there was considerable scatter in the data. The Cate-Nelson critical levels for K were 0.20 and 0.24 cmol kg-1 for the Mehlich 3 and neutral, 1N ammonium acetate extractants, respectively. On this basis it appears that the Mehlich 3 is at least as good as the currently used extractants for P and K and could readily replace them in Pennsylvania. At the same time the large amount of scatter indicates the need for a more mechanistic approach to soil testing.
A soil nitrate test taken about 4 weeks after emergence has been proposed to predict the corn (Zea mays L.) yield response 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. Five extracting solutions including distilled water, 0.01M CaCl2, 0.02M CaCl2, 0.025M Al2(SO4)3, and saturated CaSO4 were also evaluated for use in the kit.
Extracting solutions were evaluated on the basis of their effect on strip color development, flocculating properties, potential for preparation of an extracting solution concentrate, and the comparison of quicktest analyses to results from a standard laboratory method. The standard deviation for weighing samples with an inexpensive egg scale was approximately six times less than when samples were taken with a standard 20 g scoop. Standards prepared in the different extracting solutions indicated differences in strip color development existed. Based on solubility and flocculating properties, 0.025M Al2(SO4)3 and 0.02M CaCl2 extracting solutions were selected for comparison to the laboratory method. From this evaluation, 0.025M Al2(SO4)3 was selected for use in the quicktest kit. A list of components of the quicktest kit is included. Use of the quicktest can increase the acceptance of the soil nitrate test for corn, and ultimately improve N use efficiency and minimize nitrate pollution problems.
Use of a presidedress soil NO3- test (PSNT) for corn (Zea mays L.) could help to minimize uncertainties associated with managing N contributions from manure and legume crop residues. Understanding the performance and impact of this test under a wide range of conditions is necessary to target its use. A proposed quicktest method could improve the utilization of this test. This study was established to evaluate: (i) soil NO3- levels at sidedressing and the impact of the PSNT on fertilizer use under a range of field history classifications and (ii) the accuracy of the quicktest performed by persons with minimal laboratory experience. Quicktest kits were developed and distributed to extension agents and crop consultants. These cooperators offered free soil testing to farmers and collected field history information on each sample they analyzed (2725 samples). A subset (610 samples) was sent to a soil testing laboratory to compare quicktest and standard laboratory results. Quicktest accuracy was less than the laboratory method but adequate to ensure recommendations within 25 lb of the laboratory recommendation in 82% of the cases. Soil NO3- levels in manured fields were 3.3 ppm higher than nonmanured fields. Soil NO3- levels from fields following alfalfa (Medicago sativa L.) without a manure history were not different than fields with no legume and no manure, indicating the PSNT did not account for the increased N availability from alfalfa residues. Based on this research, the PSNT is effective to reduce unnecessary N applications to corn, particularly where high soil NO3- levels result from manure applications.
This document was last modified on January 3, 2007.