Warm Season Forages and Nitrogen Study

Objective:       

To evaluate the nitrogen response of seven warm season grasses under different levels of nitrogen fertility and contrasting moisture regimes

Personnel:                                                                                          MFAC      

Jessica A. Torrion, Eeusha Nafi, Daniel Porter                                                                                                                              

Summary:

The trial was planted on May 27-28, 2021. The detailed management information is provided in Table 1. The seven forage species planted were pearl millet (Tifleaf 3), sudangrass (Piper), teff (Corvallis, 20BAR_ET), and three sorghum-sudan species (S5501, AS6402, S6504) with cutting intensities provided (table 2). The study was conducted in irrigated and rainfed environments. The rainfed environment received 4.3 inches of rainfall, and the irrigated environment received an additional 8 inches of irrigation.

Under rainfed, all grass cultivars did not respond to nitrogen rates except the sorghum-sudangrass (S5501), which responded to 233 lbs N/A available in the soil. However, this response is considered economically risky. The crude protein in Teff (20BAR_ET) and two sorghum-sudan (AS6602 and S5501) responded to the high N rates. No crude protein response with the rest of the cultivars. Overall, crude protein in teff was higher than others due to its relatively lower yield. Yield and crude protein have inverse relations (Figure 1). There is no interaction with the cultivar and N levels for water-soluble carbohydrates (WSC). The WSC, in general, increases with N levels. The relative feed value (RFV) was related to either N or cultivar. Generally, RFV increases with N. Also, teff and pearl millet tend to have higher RFV than others.

Under irrigation, teff yields (Corvallis and 20BAR_ET) did not respond to N. The yield response with N either plateaud or decreased as N further increased for the rest of the species. For pearl millet, sudangrass, and sorghum-sudangrass (only for S5501 and S6504), they pushed their yield potential under irrigation and 253 lbs/A total N. Although, the sorghum-sudangrass (AS6402) had its maximum response at 193 lbs/A under irrigation.  Only the Piper sudangrass’ crude protein did not respond to N levels. Overall, teff species have superior crude protein but lower WSC than others. The WSC of all sorghum-sudangrass species, in general, have higher WSC but do not respond to N (except S6504, where the highest WSC was observed in the highest N level). Overall, the RFVs of the teff species are superior to others. Only the sudangrass (Piper) and  sorghum-sudan (S5501) RFVs did not respond with N.        

Table 2. Trial entries, seeding rates, and number of cuttings

Table 3. Nutrients applied in 2021. Total N supply includes the residual (73 lbs/A) + faba credit (20 lbs/A) + the applied nitrogen using urea and the N associated with the applied monoammonium phosphate.

Table 4: Total forage yield and average quality with nitrogen (N) under rainfed. The total N comprises of: 1) soil residual nitrates, 2) applied fertilizers, and 3) credit from previous Faba.

YLD, yield; CP, crude protein; WSC, water-soluble carbohydrates; RFV, relative feed value; ns, not significant  

Table 5: Total forage yield and average quality with nitrogen (N) under irrigation. The total N comprises of: 1) soil residual nitrates, 2) applied fertilizers, and 3) credit from previous Faba.

YLD, yield; CP, crude protein; WSC, water-soluble carbohydrates; RFV, relative feed value; ns, not significant

Figure 1: Total forage yield (sum of all cuttings) and average crude protein content (mean of all cuttings) relationship between forage yield and crude protein contents across species, nitrogen, and environments.