Research at SDSU shows that current soil tests are doing a good job indicating nitrogen fertilizer needed by corn, says Dr. Ron Gelderman of the SDSU Plant Science Department.

Gelderman presented a research paper entitled "Relation of Nitrogen Uptake and Yield of Corn With Several Soil Nitrogen Availability Indices" at the annual meeting of the American Society of Agronomy in Anaheim, California.

The preliminary data of the project is based. on two years of research conducted at 21 test sites throughout eastern South Dakota.

"The purpose of soil testing is to evaluae soil fertility so accurate fertilizer recommendations can be made. There are several steps involved in soil testing including sampling, analysis, correlation, calibration and interpretation. Our present concern with this research is correlation, which indicates the reliability of the soil test," said Gelderman.

"We found that the nitrate nitrogen soil test correlated the best. The samples taken to four feet correlated better than those taken at a shallower depth. The results imply that a deeper test may be more accurate, but practicability has to be kept in mind," said Gelderman.

"It is encouraging to look at the relationship between nitrate nitrogen and the yields that were obtained, because they differ only slightly from our present relationship. This is good, as it indicates that we are on the right track when making nitrogen recommendations," said Gelderman.

"We are trving to determine the best test or tests to use with corn," said Gelderman. This is accomplished by comparing corn grown without nitrogen to corn grown with adequate nitrogen in the test plots. The relative yield of the no nitrogen treatment is then related to the soil test. If a soil test is working, low relative yields are associated with low level tests, and high relative yields with high soil tests.

He added . that measuring organic nitrogen that will be released into the soil throughout the season could also that a successful means of predicting soil nitrogen that will be available to the crop. Gelderman also mentioned that perhaps we can make even better recommendations in the future by using the test along with the nitrate nitrogen test.

"This research should provide South Dakota with a good data base for nitrogen recommendations. In the past South Dakota has done much research of this nature with small grains, but not with corn. We had been using data for corn from other states," said Gelderman.

"Applying the correct amount of nitrogen and other fertilizers is very important," said Gelderman.