Developing a practical guide to using the CSNT and ISNT for improved nitrogen balances on dairy farms

With the continuing rise in crop input costs farm mangers are interested in tools that allow them to properly credit the nutrients they have on the farm (manure, compost, cover crops, plant residues from crop rotations, etc.) and minimizing purchased fertilizer. The Illinois Soil Nitrogen test (ISNT) and corn stalk nitrate test (CSNT) are two management tools that can be used to illustrate where adjustments to N management for corn can be made, using an adaptive management approach with farmers as decision makers. While a growing number of farm managers see the value of the CSNT and ISNT information, feedback showed the need to find (1) more efficient and lower cost methods to gather the samples and run the tests, and (2) a more straightforward process to interpret the results.

This project addressed three practicality questions raised by farmers: (1) can CSNT samples be collected after harvest rather than walking through standing corn (time reduction); (2) can certain fields be targeted or should the whole farm be sampled; and (3) what is the cost of sample collection and testing compared to the benefits of reduced N fertilizer.

For the two farms in the project, all corn fields were sampled in fall 2011 with followup sampling for fields that remained in corn in fall 2012. Based on feedback from the two farmers and their advisors and other farm teams with experience with the test, and based on an evaluation of the impact of sampling protocol on CSNT values, a new protocol was developed and introduced at the 2012 NRCCA training held at the end of November, 2012, and attended by 73 certified crop advisors.

The new protocol is documented in Agronomy Factsheet 72 (“Taking a Corn Stalk Nitrate Test Sample After Corn Silage Harvest”, 11/21/2012) downloadable from our NMSP website: http://nmsp.cals.cornell.edu/publications/factsheets/factsheet72.pdf). Additional factsheets were developed featuring the adaptive management approach, on-farm research, and fine-tuning N management with the combined use of ISNT and CSNT (http://nmsp.cals.cornell.edu/guidelines/factsheets.html). Both farms considered whole farm CSNT sampling most useful for making management decisions, but would consider taking a subset of a minimum of six fields. Savings in fertilizer costs greatly depend on the distribution of CSNT levels and common practice (manure versus fertilizer use). Farm advisors (consultants) involved with the project have added the CSNT to the tools they recommend for farmer clients to evaluate N management of corn.

Introduction:

True to the old adage “you cannot manage what you do not measure”, data-driven decision making results in positive management changes that have measurable economic, social, and environmental impact at the farm level. This was shown by a group of 54 farms that completed whole farm nutrient mass balance (NMB) assessments for 4 years; on average, these farms achieved a 30-50% reduction in nitrogen (N), phosphorus (P), and potassium (K) use as measured by whole farm NMBs. While the NMB indicates an annual accumulation or loss of nutrients from the farm (nutrient excess or deficiency on a lb/acre or lb/cwt basis), it does not specifically identify the main drivers of the balances. As a result, farm managers made changes on a trial and error basis; we would like to make this a more directed process, and farmers have asked for guidance and tools for decision making for N fertilizer and manure use, recognizing the need to have actual verifiable data.

In recent years, two tools were evaluated, calibrated for local production conditions, and made available to farms to aid in N management decision making. The Illinois Soil Nitrogen Test (ISNT) is an organic N test that is an indicator of soil N supply potential (N expected from readily mineralizable organic matter). The Corn Stalk Nitrate Test (CSNT) allows managers to retrospectively evaluate if the corn had sufficient, insufficient, or excess N available that year (“a report card” to be used as guidance for the following year). Combining both tools allows farmers to measure, evaluate, and refine manure and fertilizer application strategies for delivering the right amount of N. In a previous project aimed at identifying nutrient management tools for small dairies, farmers identified soil testing and the CSNT as effective tools for small farms (http://nyfvi.org/default.aspx?PageID=2257&NewsID=276). Similarly, larger farms benefited from the test package.

Three main issues were identified in previous year: (1) can we make sampling for CSNT more practical (sampling after harvest rather than walking through standing corn); (2) do we need to sample the whole farm or can we target fields?); and (3) relating cost of sample collection and testing to benefits of reduced N fertilizer cost or reallocation of manure.

The Nutrient Management Spear Program CSNT database shows several farms have been assessing just one or two fields for CSNT raising questions related to transferability to other fields. Sampling more farm fields could result in a more complete whole farm N use evaluation and facilitate quicker improvements in N use efficiency (greater trust in data), reducing N losses to the environment and increasing farm profitability, but this creates an additional workload and will add to the costs.

This project, initiated by ideas from two dairy farm management teams, aims to identify a more practical and effective sampling process for the ISNT and CSNT for use by farmers and their advisors, independent of farm size.