Nutrient Management for Sustainable Soil Productivity

There was a 5% return rate of clientele for submitting soil samples to NMSU for the time interval analyzed. Thirty percent of clients requesting organic recommendations returned for additional recommendations. Irrigation water management continues to be an important aspect to controlling nitrate leaching but continues to be problematic when faced with a need to leach for salinity control.

NMED permitted dairy farms with fields with excessive levels of nitrogen in the top three feet of soil were reduced by switching from corn/wheat rotation to perennial alfalfa. The use of improved, salt tolerant varieties of alfalfa also had an impact on crop yield which further improved nitrogen removal from fields and prevented movement of nitrate into groundwater resources by reducing surface soil nitrate concentrations. The NMSU Soil Test Interpretation Workbook now includes alfalfa with nitrogen removal rate when using dairy manure or effluent water. Organic recommendations also helped reduce the use of synthetic fertilizers as the nutrients in the organic amendments are accounted for and credited toward the nutrients needed for good plant growth. By giving credit where credit is due the impact is in both better yields and reduced source material for potential contamination of groundwater resources.

A total of 959 soil samples were evaluated for nutrient content so that guidance could be given to 468 clients as to what fertilizers or organic amendments could be added or incorporated into their rotations to soil to meet crop needs. Twenty clients requested organic amendment recommendations which resulted in manures, seed meals, or legume rotation recommendations to meet their cropping system goals. Nutrient recommendations were not always needed for clients as sufficient nutrients were already present. Water management practices were suggested in cases of high soil nitrate levels in order to reduce the chance for leaching nitrate to below the root zone. Clientele that were from dairies received recommendations to grow alfalfa as a means of removing excess nitrate-N from the soil profile and reduce risk of leaching to below the root zone and into groundwater. There was an 80 percent adoption of suggested amendment application as garnered from telephone interviews. Test scores increased from an average pretest score of 72% right to 88% after the lecture regarding nutrient management. However, the single most commonly missed question both before and after the quiz was regarding fertilizer grade. Scores improved after changes were made to the lecture on NM Fertilizer Law.

A project with the Southern Region Water Quality group demonstrated that the Soil Test Interpretation workbook is able to adequately predict nitrogen availability to plants when the source material is known. Nitrogen fertilization under furrow or flood conditions was shown to be highly inefficient where a significant portion of the nitrate-N observed before irrigating had leached below the sampling zone. High levels of nitrates in subsoils from selected farms also demonstrated the mobility of nitrate and the need to manage irrigation water to avoid excessive leaching. Over-winter irrigation events are most likely to bring about leaching events with shallow-rooted annual crops.

Most private consultants report that yearly samples are taken but different laboratories are used for determining the nutrient values. Of those that do re-use the NMSU lab it amounts to 1 or 2%.

Fertilizer cost, over the past 5 years, has been shown to be the largest single controller of application rates. However, credit is much more likely to be given to manure and effluent water applications as well as previous legumes.

Private consultants that use the NMSU Soil Test Interpretation workbook report that their clients are able to apply manure and effluent water for crop production and avoid regulatory punishment for non-compliance. Credit is given to those consultants for effectively communicating the nuts and bolts of land application strategies to match with Water Quality Control Commission standards.