Emmaline Long, Quirine Ketterings, Meghan Hauser, Willard DeGolyer
Nutrient Management Spear Program, Department of Animal Science, Cornell University, Ithaca, New York
Access to accurate yield records is essential if we want to identify limitations to crop production on individual farms, fields, or portions of fields, and to improve field and farm productivity over time. We also need to know yields to evaluate where investment of additional resources (labor, nutrients, seed, lime, tile, etc.) will result in an increase in yield.
Until the introduction of forage yield monitors, the only accurate way to determine whole-farm crop yields was with the use of farm scales combined with estimations of forage moisture obtained using microwave ovens or Koster testers. Portable axel truck scales can be used as well, but use of such scales (1) introduces greater error in yield estimates as typically not all axels can be weight simultaneously, and (2) slows down the harvest process. Driving trucks over permanent farm scales located close to the bunks causes less of a delay but still impacts the harvest process somewhat. Thus, few farms have long-term yield records. One exception is Table Rock Farm in Western New York where all truck-loads of all corn and hay fields have been weighed and recorded over the past fourteen years. Here we analyzed the yield data from this farm to: (1) determine the temporal variability of forage yields (corn silage, alfalfa/grass mixtures, and overall dry matter (DM) production); (2) assess yield and yield stability over time across all fields with at least two crop rotations; (3) evaluate soil physical and chemical properties as potential indicators of yield and yield stability over time; and (4) develop a method to analyze yield data.
Yield Data and Analyses
Yield was measured between 2000 and 2013. Spatial (field to field) and temporal (same field over years) variability was determined using 107 fields of which 61 had yield data for six corn years each and 71 fields had five full production years for alfalfa/grass mixtures. The average yield and coefficient of variation (CV for means over time) were calculated for each field. The fields were divided into four groups called quadrants (Q1-Q4), using the overall weighted mean yield and mean CV as cutoffs for the quadrants: (1) above mean yield, below mean CV (Q1); (2) above mean yield, above mean CV (Q2); (3) below mean yield, above mean CV (Q3); and (4) below mean yield, below mean CV (Q4). This methodology allowed us to identify fields that are consistently high yielding versus fields that sometimes yield high, sometimes low, or are consistently low in yield. The consistently high yielding fields are the fields with the greatest biological buffering capacity, able to produce also under challenging weather conditions.
Corn yields increased over time from 5.9 tons/acre dry matter (DM) in 2000 to 7.9 tons/acre in 2013 (from 16.9 to 22.6 tons/acre at 35% DM). The yield of alfalfa/grass mixtures did not increase, averaging 3.8 tons/acre DM (4.5 tons/acre at 85% DM). In 2013, the average yields for corn silage and alfalfa/grass mixtures on the case study farm were 37% and 22% higher than the state average that year. Growing degree days since planting and whole-season (March through October) rainfall were not correlated with yield of either corn or alfalfa/grass mixtures. Corn silage yield was impacted by rainfall during March and April, and during July and August. An increase in rainfall during March and April, just prior to corn planting, caused a decrease in overall yield. In contrast, an increase in rainfall during July and August, a time period in which tasseling occurs, was correlated with an increase in overall yield (Fig. 1). The yield of alfalfa/grass mixtures was not correlated with rainfall during individual months (data not shown), but increased with total rainfall in July and August (Fig. 1).
Corn silage average yield across fields and years was 7.0 tons/acre dry matter, with a mean CV of 16.4% (Fig. 2). In contrast, the overall yield for alfalfa/grass mixtures was 4.4 tons/acre dry matter, with a mean CV of 21.6% (Fig. 2). For corn and alfalfa-grass mixtures yielding above the farm average, there was a 74% and 86% probability of a CV below the farm average, respectively, indicating that high yielding fields tend to be more consistent in yield over time than low yielding fields.
The fields in Q1 and Q2 had a higher percentage of well-drained soils, versus primarily moderately and somewhat well-drained soils for Q3 and Q4. These results suggest that drainage of the soil and field yield and stability are correlated; higher yields are expected in better drained soils. It is important to keep in mind that these results are based on the predominant soil type in the field, and may not be the only driving force behind the overall performance. It is therefore important to also consider chemical properties when quantifying spatial variability.
Organic matter for consistently high yielding fields averaged 2.9 and 3.2% for corn silage and alfalfa/grass mixtures, respectively, versus 2.7 and 2.8% OM for low and variable yielding fields. Fields in alfalfa/grass mixtures with a lower than average CV had significantly higher OM levels suggesting a positive link between OM and yield and yield stability over time.
Consistently high yielding fields averaged 36 and 40 lbs P/acre on the Cornell Morgan soil test for corn silage and alfalfa/grass mixtures, respectively, versus 18 lbs P/acre for low yielding and more variable fields. Corn silage fields with a below average CV (less variable over time) had higher mean soil test P than those with a higher than average CV. High yielding fields with alfalfa/grass mixtures had higher soil test P than low yielding fields. However, across all fields for both crops, yield increased as Cornell Morgan soil test P increased up to 32 lbs P/acre for corn silage, and 29 lbs P/acre for alfalfa/grass (Fig. 3); there was no relation between yield and soil test P at soil test levels that were higher than these values reflecting past manure applications and indicating it is not the P in the manure that is linked with the high yielding fields but more likely the benefits of organic matter addition and stimulation of microbial activity with the addition of manure.
Summary and Conclusions
Corn silage yields increased from 2002-2013, while yields of alfalfa-grass mixtures remained constant over time. Yield varied both temporally with rainfall throughout the growing season and spatially among fields. The consistently high yielding corn fields exceeded 7.0 tons/acre dry matter with a CV less than 16.4%. Fields in alfalfa-grass mixtures that were consistently high yielding exceeded 5.5 tons/acre with a CV less than 21.6%. The highest and most consistently yielding fields had better-drained soils, optimum or higher in soil test P, and higher OM levels than the lower yielding and more variable fields. These results could suggest that farmer practices that improve soil drainage (tile drainage), conserve or even increase organic matter (reduced tillage and cover crops), and enhance soil test P (manure application) to optimal (not excessive) levels, might be effective in increasing the overall corn silage yield and yield stability. Similar assessments can be done (and much faster) when analyzing forage harvester yield maps. Such work is ongoing in the Nutrient Management Spear Program.
Funding was provided by a USDA-Conservation Innovation Grant and a NESARE grant. For questions about these results contact Quirine M. Ketterings at 607-255-3061 or firstname.lastname@example.org, and/or visit the Cornell Nutrient Management Spear Program website at: http://nmsp.cals.cornell.edu/. For more details on the study, see our article in Agronomy for Sustainable Development DOI 10.1007/s13593-016-0349-y (Long and Ketterings, 2016).