A Simple Soil Test for Detecting Sites that are Nonresponsive to Nitrogen Fertilization
- S. A. Khana,
- R. L. Mulvaney *a and
- R. G. Hoeftb
Recent work indicates that accumulation of amino sugar N in soil reduces the yield response of corn (Zea mays L.) to N fertilization, and that nonresponsive sites are detectable by determination of amino sugar N in soil hydrolysates. Unfortunately, the hydrolysis process is too complicated and time-consuming for use in routine soil testing. A much simpler technique was developed to estimate amino sugar N without the need for acid hydrolysis. In this test, 1 g of air-dried soil is treated with 10 mL of 2 M NaOH in a 473-mL (1-pint) wide-mouth Mason jar, and the sample is heated for 5 h at 48 to 50°C on a hot plate to liberate (NH4 + amino sugar)-N as gaseous NH3 The NH3 is collected in H3BO3–indicator solution, and subsequently determined by acidimetric titration. Recovery ranged from 97 to 102% when analyses were performed after treating samples with 15N-labeled (NH4)2SO4 or glucosamine, but did not exceed 6.5% with labeled glycine and was undetectable with labeled NO3 or NO2 Comparative studies using 12 nonresponsive and 13 responsive soils showed a very high correlation between soil-test N and hydrolyzable amino sugar N (r = 0.90***). Test values were significantly higher (P < 0.001) for nonresponsive (237–435 mg N kg−1) than for responsive (72–223 mg N kg−1) soils. The soil test described has important economic implications for production agriculture, and also should be of value for controlling NO3 pollution of ground and surface water.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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