- Agronomic: corn
- Animals: bovine
- Animal Products: dairy
- Animal Production: feed/forage, manure management
- Crop Production: cropping systems, crop rotation, double cropping, drought tolerance, fertilizers, nutrient cycling, nutrient management, water management
- Education and Training: on-farm/ranch research
- Production Systems: integrated crop and livestock systems
To reduce nutrient loading in waterbodies, farms are encouraged or mandated to develop nutrient management plans. Reducing the potential of nutrient runoff to surface water can keep nutrients above ground. We hypothesized that increasing corn planting density can be used strategically to increase N and P recycling through the soil-crop system. Therefore, the objective of this study was to evaluate the effects of corn planting density with different fertilizer rates on forage biomass yield, silage quality and digestibility, and N and P removal from the soil in a commercial dairy farm. This on-farm study was performed at a 425-cow commercial dairy farm located in Crockett, VA. During the springs of 2017 and 2018, a conventional (CONV) corn hybrid and a brown midrib (BMR) corn hybrid were planted at a theoretical seeding rate (i.e., treatments) of 60,000, 75,000, and 90,000 seeds/ha (60K, 75K, and 90K, respectively). Four plots (2.3-m wide and 25-m long) were planted for each treatment and hybrid, therefore leading to 24 plots for each field in each growing season. Also, when the crop showed 6 visible leaves (V6), all plots were split into half plots (hereafter known as subplot), and each subplot was fertilized with either 50 or 100 kg N/ha as UAN (1N and 2N, respectively). At harvesting, 10 plants were cut by hand at 15 cm above ground. Whole plants were weighed and chopped for chemical and digestibility analyses. The experiment was designed as a split-plot in a completely randomized design. All variables were analyzed using the MIXED procedure of SAS, and the statistical model included the fixed effect of year (degrees of freedom, df = 1), the fixed effect of field (df = 1), the fixed effect of treatment or planting density (fixed; df = 2), the fixed effect of corn hybrid (fixed; df = 1), the random whole-plot error (df = 72), the fixed effect of fertilization (df = 1), all 2-, 3-, 4- and 5-way interactions (df = 41), and the random split-plot or residual error (df = 72). Resulting populations were 63,200, 72,600, and 86,300 plants/ha for 60K, 75K, and 90K, respectively. Planting corn at the highest population (90K) resulted in the greatest biomass yield (21.4 Mg/ha), whereas biomass yield was similar for the intermediate (75K) and the lowest (60K) corn planting population (20.3 Mg/ha). Doubling the dosage of N fertilizer increased biomass yield only by 3.1%, and the conventional hybrid yielded 19.2% more than the BMR hybrid (22.5 vs. 18.9 Mg/ha, respectively). Planting corn at the highest population (90K) resulted in the lowest concentration of crude protein (81 g/kg), whereas the concentration of crude protein was similar for the intermediate and the lowest corn planting population (84 g/kg). Due to the negligible differences in biomass yield and crude protein concentration, the removal of N from the soil did not change by increasing corn planting population (276, 271, and 269 kg/ha for 60K, 75K, and 90K, respectively). Doubling fertilization increased N removal by 21 kg/ha. Planting corn at the lowest population (60K) resulted in the greatest concentration of P (266 mg/kg), whereas the concentration of P was similar for the intermediate and the highest maize planting population (257 and 255 mg/kg, respectively). Contrary to our hypothesis, the removal of P from the soil did not change by increasing corn planting population (55, 53, and 56 kg/ha for 60K, 75K, and 90K, respectively). Neither corn planting population nor N fertilization affected the in vitro dry matter digestibility or the in vitro neutral detergent fiber digestibility of corn silages. In conclusion, under the conditions of this on-farm study, increasing corn planting density did not increase the removal of neither N nor P from the soil.
Increasing corn planting population can substantially increase corn silage yields. Cusicanqui and Lauer (1999) reported that the greatest dry matter yields were obtained when corn plant population was increased to 98,000 plants/ha. Similarly, Ferreira et al. (2014) reported that forage yields increased linearly and by 41% when plant population was increased from 60,000 to 90,000 plants/ha. In a more recent study, Ferreira and Teets (2016) also reported higher forage yields when corn planting population was increased from 55,000 to 100,000 plants/ha. An interesting observation from the latter studies was the similar nutrient composition of the forages obtained when corn was planted at different planting populations (Ferreira et al., 2014; Ferreira and Teets, 2016).
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 population (Ferreira and Teets, 2016). To reduce nitrogen (N) and phosphorus (P) loading in waterbodies, dairy farmers or managers are encouraged or mandated to develop nutrient management plans (Bosch et al., 2006; DCR, 2014). For dairy farming systems, there are three types of practices for reducing nutrient upload in waterbodies: 1) reducing nutrient excretion in manure, 2) reducing the amount and changing the method and/or timing of fertilizer application to reduce nutrient runoff, and 3) reducing the potential of nutrient runoff to surface water (Dou et al., 2001; Bosch et al., 2006). The use of stream buffers, conservation tillage, and cover crops are common means of reducing nutrient runoff. The purpose of these practices is to increase the utilization of nutrients, keeping them above ground, and therefore reducing the potential runoff.
As more biomass was harvested without affecting the N concentration of the biomass, the increased yield of corn for silage translated into a greater uptake of N from the soil (Ferreira and Teets, 2016). As N is one of the two nutrients for which dairy farmers need to prepare nutrient management plans, increasing corn planting population can have great relevance enhancing environmental quality of farm operations. 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 population of corn for silage (Bosch et al., 2006).
For this study, we hypothesized that increasing corn planting population can be used strategically to increase N and P recycling through the soil-crop system (Powell et al., 2008), while increasing forage production and maintaining forage quality in dairy farming systems (Ferreira and Teets, 2016). Therefore, the objective of this study was to evaluate the effects of corn planting population with different fertilizer rates on forage biomass yield, silage quality and digestibility, and N and P removal from the soil in a commercial dairy farm.