Broiler Litter Fertility Regimes Influence Forage Nutritive Value of Sorghum-sudangrass

Broiler Litter Fertility Regimes Influence Forage Nutritive Value of Sorghum-Sudangrass

Byron B. Sleugh, Associate Professor, Rebecca A. Gilfillen, Associate Professor, and William T. Willian, Associate Professor, 1906 College Heights Blvd. #41066, Department of Agriculture, Western Kentucky University, Bowling Green 42101-1066

Abstract

Fertility regimes for sorghum-sudangrass [Sorghum bicolor (L.) Moench] that include broiler litter and that can produce similar forage yield and quality to inorganic fertilizer while reducing nutrient loading have not been fully investigated. Unfortunately, many producers still apply broiler litter and other animal manures on a nitrogen basis and thereby over-apply phosphorus which can lead to potential pollution problems. This research focused on identifying fertility programs utilizing broiler litter applied based on plant P requirement but which would still produce forage yield and quality comparable to that produced using inorganic fertilizer. Our results show that lower rates of broiler litter, applied based on the P requirement of the crop and supplemented with inorganic N, can produce forage with similar nutritive value to that fertilized with inorganic fertilizer only or broiler litter applied to meet crop N requirements.

Introduction

Broiler (Gallus gallus) production has increased ten-fold in Kentucky over the last 8 years (8) and continues to increase in the Southeast United States. Many farmers are attracted to broiler litter (a mixture of chicken manure, wasted feed, wood shavings or crop residue such as rice or peanut hulls, and feathers) as an alternative nutrient source for their forage crops because it is inexpensive and in some cases very readily available. Broiler litter is often over-applied to fields in close proximity to broiler production areas in an effort to "dispose" of the litter. This practice may cause water pollution and soil nutrient imbalances. Long-term application of broiler litter to soils can lead to an accumulation of soil nutrients including P, K, Cu, and Zn (10,14) and can have adverse environmental impacts (9). Even with these risks, Kingery et al. (9) concluded that land application remains the most practical way to manage large quantities of broiler litter.

Crops receiving nutrients from broiler litter can be harvested as hay or silage in an effort to export the nutrients from the site where they were applied. Forage crops remove a relatively small quantity of some nutrients relative to the amounts of those nutrients applied but hay production is an important component of nutrient management (4). Additionally, high-yielding hay crops will remove more nutrients because nutrient removal is a product of forage yield and nutrient concentration (13). Broiler litter as a source of N has been used to produce forage with yield and nutritive value that is equal to or better than forage fertilized with ammonium nitrate (16). Generally, broiler litter is slightly greater in N than P. However, forage crop requirement for N is considerably greater than the requirement for P. Because of this difference in the concentration of the various nutrients contained within broiler litter, one nutrient (for example N) may be undersupplied while another (for example P) is oversupplied, thus creating a potential pollution problem.

Sorghum-sudangrass has been found to be a good alternative for nutrient management hay systems in the southeastern USA (11). With the increased popularity of sorghum-sudangrass in forage-livestock systems in the region and the increased use of broiler litter as a fertilizer source, it is important to determine fertility regimes that will produce adequate forage yield and nutritive value.

Many studies (1,2,3,5,7,11) address the use of broiler litter, swine effluent, or dairy slurry as a nutrient source for crops but these materials are usually applied based on the N requirement of the crop or on consistent tonnage (flat rate) or comparative rates. It is important to develop management strategies for applying animal wastes based on crop P requirements to help reduce nutrient loading. Therefore, the objective of this study was to determine broiler litter fertility regimes for sorghum-sudangrass that would produce comparable forage yield and nutritive value to that of inorganic fertilizers alone while reducing the potential for excessive accumulation of some soil nutrients.

Field Experiment, Data Collection, Analysis, and Interpretation

Sorghum-sudangrass plots (8 × 100 m) were established in 2001, 2002, and 2003 at Western Kentucky University’s Agricultural Research and Education Complex in Bowling Green, KY on a Pembroke silt loam (fine-silty, mixed, mesic Mollic Paleudalf) with a pH of 5.1. Mean monthly temperature and precipitation for the growing season (April to October) are shown in Fig. 1 and Fig. 2, respectively. Soil samples (15-cm depth) were taken prior to planting to determine fertility needs for each plot. The initial soil analysis of the plot site before any treatments were applied indicated 70, 2.58, 187, and 3.03 mg/kg for P₂O₅, Cu, Fe, and Zn, respectively. The nutrient content of the litter (Table 1) was determined and the amount of litter or inorganic fertilizers applied (Table 2) was based on soil test results obtained for the field each year. Nitrogen and P were assumed to have 50% and 80% availability from the broiler litter, respectively. Plots were disked twice, fertility treatments applied, incorporated with a spring-tine harrow, and cultipacked prior to planting. Fertility treatments used were: (i) broiler litter applied at the recommended nitrogen rate (Litter-N); (ii) broiler litter applied at the recommended phosphorus rate (Litter-P); (iii) broiler litter applied at the recommended phosphorus rate with supplemental inorganic nitrogen to meet crop nitrogen needs (Litter-P+N); and (iv) recommended inorganic fertilizer. All treatments were applied prior to planting once for the season and were reapplied on the same plots in each of the three years.

Fig. 1. Monthly and 30-year average temperature for the growing season (April to October) in 2001, 2002, and 2003.

Fig. 2. Monthly and 30-year average precipitation for the growing season (April to October) in 2001, 2002, and 2003.

Table 1. Nutrient composition (as received) of broiler litter applied in 2001, 2002, and 2003.

Year	N	P₂O₅	K₂O	Cu	Fe	Zn
Year	(g/kg)			(mg/kg)
2001	36.2	45.3	27.2	523	1835	617
2002	29.3	30.9	20.6	458	978	419
2003	28.1	34.1	22.7	329	874	283

Table 2. Broiler litter and actual inorganic fertilizer nutrients applied to sorghum-sudangrass in 2001, 2002, and 2003.

Fertility treatment	2001	2002	2003
Litter-N	7.3 Mg/haBL^x	10.7 Mg/haBL	10.8 Mg/haBL
Litter-P	1.4 Mg/haBL	1.3 Mg/haBL	0.8 Mg/haBL
Litter-P+N	1.4 Mg/ha BL and 53 kg/ha N	1.3 Mg/haBL and 116 kg/ha N	0.8 Mg/haBL + 188 kg/ha N
Inorganic fertilizer	190 kg/ha N 45 kg/ha P₂O₅ 79 kg/ha K₂O	156 kg/ha N 33 kg/ha P₂O₅ 39 kg/ha K₂O	233 kg/ha N 33 kg/ha P₂O₅ 48 kg/ha K₂O

^x Broiler litter.

Plots were harvested three times in 2001, and twice in 2002 and 2003 when the crop was at the boot to early head stage. An area 0.81 × 3 m was harvested at a height of 5-cm with a sickle-bar mower to be used for yield determination. Random forage samples were collected from each plot prior to harvest by clipping 15 plants at a 5-cm height, chopping, and combining them to form a composite sample for that plot. The rest of the plot was then harvested as hay and removed from the field. Composite samples were weighed, dried in a forced-air dryer at 60°C for 48 h, weighed again, and then ground to pass through a 1-mm screen. These samples were used to determine forage dry matter content and nutrient concentration. In addition to the mineral concentration (P, Cu, Zn, and Fe) we measured ADF, CP, and NDF because many producers will use these parameters as their sole indicator of forage nutritive value. A set of calibration samples were used to determine CP, ADF, NDF, P, Cu, Zn, and Fe and the other samples were predicted using near-infrared reflectance spectroscopy (17). Crude protein was determined using a Leco-528 nitrogen combustion analyzer (Leco Corp., St. Joseph, MI) while ADF and NDF were determined using the Georing and Van Soest (6) method. The concentration of P, Cu, Zn, and Fe were measured using a Perkin Elmer 3300 XL ICP (Shelton, CT).

The experimental design was a randomized complete block with four replications. Statistical analysis was performed with the General Linear Model (GLM) procedure of SAS (SAS Institute Inc., Cary, NC). Mean comparisons were made with an F-protected LSD (15) at P ≤ 0.05 unless otherwise noted. Data for each year are presented separately because there was a significant treatment-by-year interaction for the various forage nutritive value parameters and nutrient concentration. The data represent the mean of all harvests for individual treatments.

Acid Detergent Fiber, Neutral Detergent Fiber, and Crude Protein

Inorganic fertilizer plots had the greatest CP concentration but CP was similar for the Litter-P+N and Litter-N treatments (Table 3). The lowest CP was in Litter-P in 2001. This indicates that applying large quantities of broiler litter did not improve forage CP concentration compared to inorganic fertilizer and that Litter-P plots were N deficient. This finding (for 2001) agrees with that reported by Harvey et al. (6) that forage CP content was only slightly increased when higher levels of N were applied. However, in our study CP in Litter-N plots was greater than Litter-P+N and inorganic plots in 2002 and 2003 even though they received the same level of N fertilization. This was likely because treatments were applied to the same plot each year and N that was not immediately available in 2001 may have become available in 2002 and 2003. The low CP concentration in Litter-P plots may have been because this treatment did not provide enough N for formation of forage protein. Lower rates of broiler litter, applied to meet crop P requirements and supplemented with inorganic N (Litter-P+N), produced forage with similar CP concentration to inorganic fertilizer in 2002 and 2003.

Table 3. Average concentration of ADF, NDF, and CP in sorghum-sudangrass with varying broiler litter and inorganic fertilizer fertility regimes in 2001, 2002, and 2003.

Treatment	ADF			NDF			CP
	2001	2002	2003	2001	2002	2003	2001	2002	2003
	Concentration (g/kg DM)
Litter-N	359a	332c^x	357c	646a	555b	594b	111b	207a	177a
Litter-P	358a	364a	388a	642a	585a	634a	90c	142c	96c
Litter-P+N	351a	357ab	367b	641a	578ab	603b	113b	172bc	136b
Inorganic fertilizer	348a	345bc	366bc	634a	576ab	603b	121a	186ab	141b

^x Means followed by the same letter are not different at the P ≤ 0.05 level.

In 2003, all treatments except Litter-P had similar NDF while Litter-P+N, Litter-N, and inorganic fertilizer were similar in ADF concentration (Table 3). Data for 2003 were similar to that reported by Harvey et al. (7) who found that NDF and ADF of bermudagrass were not affected by level of N. Even though high rates of broiler litter (Litter-N) offered a slight advantage in ADF and NDF in 2002, if a producer is committed to reducing nutrient loading by reducing application rates, lower rates of litter should be applied (Litter-P) and supplemented with inorganic N to provide comparable ADF and NDF concentrations.

Forage Mineral Concentration (P, Cu, Fe, Zn)

In 2001, inorganic fertilizer plots had the lowest P concentrations (Table 4). However, in 2002, inorganic fertilizer plots were similar in P concentration to Litter-P and Litter-P+N. Concentration of P was similar for all treatments in 2003 except Litter-P. This may have occurred because available N in the Litter-N plots boosted yield (Table 5), and thus nutrient uptake. Adeli and Varco (1) reported that for grasses to be used in nutrient management plans, high rates of N are needed. However, our results indicate that P concentration was similar for Litter-P (low N) and Litter-P+N plots in two of three years. Additionally, Litter-P (low N) plots had similar P concentration to Litter-N plots in 2001 and 2002 and had the greatest P concentration of all treatments in 2003. Our results indicate that Litter-P+N was similar to inorganic fertilizer plots in P concentration in 2 of 3 years (2002 and 2003). Even though average total yield was similar for Litter-N and Inorganic plots, the soil concentration of P, Cu, Fe, and Zn were greatly elevated in the Litter-N plots (Table 5). This is due to residual nutrients from the previous years’ application of litter on the Litter-N plots. Soil Zn, Cu, and P concentrations were 100% greater in Litter-N plots than inorganic fertilizer plots at the end of the study period. This suggests that a producer who wishes to utilize broiler litter could reduce the amount of litter applied (apply based on crop P needs) and supplement with inorganic N and still produce forage with similar nutritive value and cause less soil nutrient accumulation.

Table 5. Sorghum sudangrass forage yield, pre-experiment and post experiment chemical characteristics of the soil at the end of the experiment period (2003).

Fertility treatment	Soil charactersistics (mg/kg DM)					Yield (kg/ha)^y
Fertility treatment	pH	P₂O₅	Cu	Fe	Zn	Yield (kg/ha)^y
Initial analysis^x	5.1a	160.3c	2.5c	187b	3.0c	N/A
Litter-N	5.9a	478.6a	6.3a	331a	8.3a	4307a
Litter-P	5.8a	309.1b	4.1b	325a	4.8b	2238b
Litter-P+N	5.9a	247.3b	3.2b	301a	3.6b	3030b
Inorganic fertilizer	5.9a	251.9b	3.4b	322a	4.1b	4447a

^x Background soil samples taken at the beginning of the experiment before the application of fertility treatments.

^y Total season yield averaged over the 3-year period.

Each treatment was significantly different in Cu concentration in 2003 (Table 4) with the greatest concentration in Litter-N, followed by inorganic fertilizer, Litter-P+N, and Litter-P, respectively. The amount of Cu supplied by the litter mineralization in Litter-P and Litter-P+N treatments was not enough to cause a difference in forage Cu concentration in those treatments in 2001 and 2002. Generally, lower Cu concentration was observed in Litter-P and Litter-P+N plots. This may have been due to a combination of the limited growth/yield (Litter-P plots) and the increased growth attributable to the supplemental N in Litter-P+N plots (Fig. 3) that caused a dilution of the nutrients. In addition, less Cu was applied due to the lower amount of broiler litter applied.

Fig. 3. Sorghum sudangrass fertilized with broiler litter based on crop P requirements and supplemented with inorganic N (left) compared to sorghum sudangrass fertilized with broiler litter based on crop P requirement and no inorganic N supplementation (right).

There was no difference in Fe concentration among treatments in 2001 and 2002 (Table 4). In 2003, the greatest concentration was seen in Litter-N plots and the lowest in Litter-P plots. Even though Fe content of the broiler litter was lowest in 2003 (Table 1) it may have taken 2 years to build up enough soil Fe to affect forage uptake. Elevated forage Fe and Cu concentration could cause toxicity problems for livestock (10). With the exception of forage Zn (2001) and Cu (2003) concentration in the Litter-P plots (Table 4), all other forage mineral concentration were higher than the minimum requirements for beef cattle but less than the maximum tolerable level (12).

Summary and Conclusion

Our results show that lower rates of broiler litter, applied based on the P requirement of the crop and supplemented with inorganic N, can produce forage with similar nutritive value to that fertilized with inorganic fertilizer only or broiler litter applied to meet crop N requirements. This is a very important finding because producers growing sorghum-sudangrass can now apply less broiler litter if they apply based on crop P requirements and therefore reduce the likelihood of soil accumulation of nutrients such as P, Cu, Fe, and Zn. Soil Zn, Cu, and P were 100% to 300% of what they were prior to the application of litter at high rates (Litter-N) after 3 years of application of broiler litter. Soil nutrient accumulation is more likely when litter is applied in an attempt to meet the N requirement of crops since very large quantities may have to be applied.

Acknowledgment

This research was funded by a grant from the USDA-ARS and is part of the National Program 206 - Manure and Byproduct Utilization.

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