To reduce nutrient loading in waterbodies, farms are encouraged or mandated to develop nutrient management plans. For dairy farming systems, there are three types of practices for reducing nutrient upload in waterbodies: 1) reducing nutrient excretion in manure, so it reduces its load on the soil, 2) reducing the amount and changing the method and/or timing of application to reduce nutrient runoff, and 3) reduce the potential of nutrient runoff to surface water. The use of stream buffers, conservation tillage, and cover crops are common means to reduce nutrient runoff. The purpose of these practices is to increase the utilization of nutrients, keeping them above ground, therefore reducing the potential of runoff through underground water.
Old and more recent studies reported that increasing corn planting density can increase substantially forage yields. Increasing forage yields while maintaining nutritional quality of the forage has major environmental implications, as there is an increased retention of nutrients above ground when increasing planting density. Nitrogen (N) and phosphorus (P) are the two nutrients for which dairy farmers need to prepare nutrient management plans. Ferreira and Teets (2016) reported that N uptake through corn silage was increased when corn planting density was increased from 22,000 to 40,000 plants per acre. In addition to suggesting a greater nutrient efficiency use, this outcome indicates that the potential of N runoff to surface water can be reduced by increasing planting density of corn for silage.
Runoff and erosion control refers to practices that reduce the potential for P delivery to surface water. Whether increasing corn planting density increases P uptake is unknown. For this study, we hypothesized that increasing corn planting density can be used strategically to increase nitrogen (N) and phosphorus (P) recycling through the soil-crop system, while increasing forage production in dairy farming systems. Increased forage production accompanied by nutrient recycling should provide a two-fold benefit enhancing economic and environmental sustainability simultaneously.
On one side, obtaining adequate amounts of good quality forage is critical for the economic sustainability of dairy farming systems. On the other side, adequate nutrient management is critical for the environmental sustainability of dairy farming systems and related watersheds. In agreement with the Southern SARE’s On-Farm Research Program focus area of ‘increasing sustainability of existing farming practices,’ we aim to evaluate cropping strategies to maximize forage yields and reduce nutrient runoff to surface water. Specifically, for this on-farm research project we propose evaluating the effects of increasing corn planting density with different fertilizer rates on forage yield, forage quality, and nutrient uptake on a dairy farm in the Southern region of the US.
For this study we hypothesized that P uptake from the soil will be increased when corn planting density is increased. This increased P uptake from the soil should reduce P buildup and runoff, therefore enhancing environmental sustainability. Therefore, the overall objective of this on-farm research project is to evaluate cropping strategies to maximize forage yields, while enhancing environmental sustainability, to ensure economic sustainability of dairy farming systems.
Location and Cultural Management
This on-farm research project will be performed in a dairy farm located in Wythe County, in the Southwest region of Virginia. Owners of this farm milk more than 200 cows, and grow all the forage needed to feed milking cows and growing heifers. The goal is to have 2 diverse “growing environments”. Therefore, 2 cornfields (hereafter named sites) will be used in this 2-year study (i.e., site and time replication). These sites will differ in their yield potential of the soil according to the farm manager’s experience. Both sites are currently on a no-till management system. Approximately 20,000 gallons per acre of dairy manure will be spread in the fields immediately before planting corn. Weed and pest control management will be performed according to standard operating procedures and recommendations for the cornfields.
This experiment is designed as a split-plot in a completely randomized design for a 2x3x2 factorial arrangement of treatments. The factors of interest are 2 corn hybrids (whole plot), 3 planting densities (whole plot), and 2 N fertilization regimes (split plot).
Treatments, Plots and Replicates
Two diverse corn hybrids (normal and brown midrib genotypes) recommended for silage production will be planted at a theoretical seeding rate of 60,000, 80,000, and 100,000 plants per acre in four replicates per treatment in each site.year. The selected seeding rates represents a wide range that include typical seeding rates utilized in the Southern region of the US. Planting will be performed with a 6-row no-till planter. Plots will consist of 3 100-feet-long rows separated by 30 inches (3 rows/hybrid). The total number of plots per hybrid within a cornfield will be 12 (i.e., 4 replicates/density x 3 densities). At approximately V6 stage of crop growth, all plots will be fertilized with 2 doses (1X vs. 2X) of nitrogen. The 1X dose will be determined according to standard operating procedures and nutrient management plans.
Soil samples will be collected from each cornfield each year before planting. In addition to this, a second soil sample will be obtained from each plot immediately after harvesting. Soil samples will be collected at 0-20 cm and at 20-40 cm of depth. All samples will be analyzed for organic matter, nitrate nitrogen, and phosphorus concentrations.
Corn plants will be harvested at approximately ½ milk-line stage of maturity (>33% dry matter concentration). For each plot, 10 plants will be cut, weighed, and chopped using a portable fodder cutter (Stanley CH2 Shredders, GXi Outdoor Power, LLC Clayton, NC). After mixing adequately, we will collect and freeze a 1-kg sample of the chopped corn to determine the nutritional composition of corn silage. To evaluate the nutritional composition of corn silage, the chopped material will be fermented using mini-silos. For this, we will place 400 g of chopped whole-plant corn into polyethylene bags (MR-1014 embossed pouches, Doug Care, CA) that will be sealed anaerobically with a vacuum-sealer (FastVac, Doug Care, CA) as described by (Der Bedrosian et al., 2012). We will store the mini-silos for at least 60 days until further analysis.
Nutritional Composition of Corn Silages
Ensiled samples will be analyzed for dry matter (Goering and Van Soest, 1970), ash (AOAC, 2000), crude protein (AOAC, 2000), neutral detergent fiber (Van Soest et al., 1991), acid detergent fiber (AOAC, 2000), lignin (Goering and Van Soest, 1970), starch (Hall, 2009), sugars (Hall, 2009) and phosphorus (Feng et al., 2015) concentrations.
Based on the standard deviation for dry matter weight of 32 g per plant, a 90% confidence interval, and four replicates per treatment, a difference of 63 g per plant can be detected with an 80% statistical power. This reflects a 20 to 25% difference in corn plant dry matter weight. Data will be analyzed using the Mixed Procedure of SAS as for a split-plot in a completely randomized design. The model will include the fixed effects of year, site, hybrid, planting density, fertilization, and 2-, 3-, 4- and 5-way interactions, and the random effects of whole-plot and split-plot errors. The effect of planting density will be evaluated posteriori for linear and quadratic effects.
This is an on-going study, for which we need to obtain samples from a second season. Final results and discussion will be available for the final report.
Educational & Outreach Activities
Effect of corn planting density on forage yields.
Effect of corn planting density on forage P and N concentration.
This is an on-going study, for which we need to obtain samples from a second season. Final outcomes will be available in the final report.
This is an on-going study, for which we need to obtain samples from a second season. Final recommendations will be available in the final report.