Developing Environmentally Sound Poultry Litter Management Practices for Sustainable Cropping Systems

[Note to online version: The report for this project includes special characters that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact Southern SARE at (770) 412-4787 or sare@griffin.uga.edu.]

Many broiler enterprises produce excess manure for environmentally safe recycling in cropping systems on available land under their control. Application rates and frequencies are often excessive. Including cover crops in rotational cropping systems, such as vegetables followed by grass forage for temporary grazing, hay, or silage, may enable producers to apply litter at higher rates more frequently, and reduce nutrient losses due to runoff.

The objectives of this study are: (1) evaluate the environmental and economic impact of broiler litter application rates and frequencies on selected vegetables; (2) investigate the feasibility of growing warm and cool season annual forage crops in rotational cropping systems to remove excess nutrients supplied by poultry litter; (3) determine nutrient loss due to runoff in a vegetable, forage, litter management system; (4) demonstrate litter management practices on grower owned land under grower conditions.

The litter rates applied for all objectives were based on soil test nitrogen (N) requirement of the crop and percent N content of the litter. Treatments were incorporated immediately after application by power tilling.

In objective 1, litter was applied at the recommended rate or at two or four times the recommended rate and either all pre-plant or half pre-plant and half side-dressed. Throughout the study, sweet corn was the spring crop followed by broccoli in the fall. Data were collected on crop yield, nutrient uptake, nutrient accumulation, and nutrient leaching. This study indicates that producers could apply all the litter preplant or in split application without affecting growth or yield of either the spring or fall crop.

Increasing litter application at more than twice the recommended rate decreased yield. Applying litter in excess of the recommended rate increases the risk of nitrate leaching into ground water. Regardless of rate applied, phosphorus (P) continued to increase in the surface 6 in. of soil. This suggests that non-point source pollution of surface waters might occur after years of continued applications of litter on sandy soils. Continuous litter application rates greater than recommended causes a subsequent increase in K concentration in the surface 1 ft. of soil which can lead to negative effects on soil salinity and lower availability of magnesium. There is little effect from litter rate increase on Mg and Ca concentration in the surface 1 ft. but does increase Ca at depths below 3 ft. Litter rate increase does not significantly effect soil pH. Neither litter rate or fertilizer blend caused any detrimental salt accumulation.

Treatments in objective 2 consisted of cropping system (spring veg.-fall veg., spring forage-fall veg., spring veg.-fall forage) with litter applied at either recommended two times the recommended rate. Litter was applied in the spring, fall, or spring and fall. Tomatoes were the spring vegetable crop followed by turnips in the fall. Sorghum-sudan was the spring forage crop with Elbon rye planted in the fall. Data were collected on yield, nutrient uptake, nutrient accumulation and leaching. This study showed litter applications in both spring and fall increased yields of vegetable and forage crop. Producers utilizing a system of spring vegetables followed by fall forage could reduce leaching of nitrogen through the soil profile as well as reduce phosphorus accumulation in the surface 6 in. of soil. Applying litter rates sufficient to meet crop needs for N, regardless of cropping system or season of application, results in P accumulation that can lead to non-point source pollution of surface water. None of the cropping systems studied had any significant effect on K or Ca. All cropping systems reduced Mg concentration at all soil depths while reducing soil pH in the surface 1 ft. A cropping system of spring vegetables followed by a fall cover crop reduces salt accumulation and leaching.

Regardless of the season in which litter is applied K, Ca, and Mg concentration as well as soil pH decreases over time. Applying litter and commercial blend fertilizer in both spring and fall tends to increase salt accumulation and leaching below 1 ft.

In objective 3, cropping systems of spring vegetable-fall forage, spring vegetable-fall fallow, and spring vegetable-fall vegetable were studied. Fertility treatments consisting of a control, the recommended litter rate, four times the recommended rate, and a commercial blend were applied. The spring vegetable crop was sweet corn followed by broccoli in the fall. Sorghum-sudan was the spring cover crop. Elbon rye was seeded in the fall. Data were obtained on NO3-N and P accumulation, leaching, and runoff. The data indicated that a system of spring vegetables followed by a fall forage could reduce leaching and accumulation of N. Leaving the soil fallow in the fall increased NO3-N leaching. Regardless of cropping system used P will continue to increase in the surface 1 ft. of soil. A system of spring vegetables followed by fall cover greatly reduced the amount of NO3-N in the soil solution. Very little NO3-N and almost undetectable amounts of P were found in runoff water. This would indicate that incorporation of litter, which would be a normal practice under row crop production, would greatly reduce the chance of surface water pollution.

Demonstrations of litter use in vegetable production has increased grower awareness of this valuable nutrient source. Several are beginning to utilize this nutrient source in their operations. One grower in particular utilized litter in his intensive watermelon production program (mulch, drip irrigation) and realized yields of approximately 72,000 lbs/ac. Another producer of greens and onions, has begun incorporating poultry litter into his fertility program. A poultry producer diversified his operation by utilizing excess litter in a vegetable production program that supplies a local grocery chain with year round vegetables as well as a roadside stand market.

Studies in Texas and Oklahoma were established in 1992 to evaluate utilization of poultry litter in vegetable production systems. Three replicated studies were established at The Texas A&M University Research and Extension Center at Overton, and at Oklahoma State University Vegetable Research Station at Bixby. These studies consisted of: (1) evaluation of poultry litter rate and frequency of application on vegetables (Texas); (2) feasibility of growing warm- and cool-season annual forage crops to remove excess nutrients supplied by litter in rotational cropping, vegetable systems (Texas-Oklahoma); (3) evaluate runoff and leaching in vegetable-forage litter management systems (Texas); (4) demonstrate litter use in vegetable production systems on grower owned land under grower conditions (Texas-Oklahoma). In all studies litter rates were based on N requirement of the crop and percent N in the litter. Rates were compared to fertilizer blends and a 0 check. Frequency of application of litter (total, split) had no significant effect on yield of vegetables. Increasing litter application to more than twice the recommended rate decreased yield as well as increased the risk of NO3-N leaching and accumulation at lower depths of the soil profile. A system of spring vegetables followed by fall forage reduced leaching of NO3-N through the soil profile and the amount in the soil solution. Regardless of the cropping system, very little NO3-N and almost undetectable amounts of P were found in runoff water. This would indicate that incorporation of litter would greatly reduce the chance of surface water pollution. Phosphorus accumulation increased in the surface 30 cm (1 ft) of soil each season regardless of cropping system or time of application. As litter rate increased, P accumulation increased accordingly. Accumulation of P from fertilizer blend treatments was found to be significantly less than from poultry litter. Due to demonstrations of litter use in vegetable production programs, grower interest and awareness of the nutrient value of poultry litter has been augmented.

Project objectives:

The objectives of this study were to: (1) evaluate the environmental and economic impact of broiler litter application rates and frequencies on selected vegetable crops; (2) investigate the feasibility of growing warm and cool season annual forage crops in rotational-cropping, vegetable systems to remove excess nutrients supplied by poultry litter; (3) determine nutrient loss due to runoff in a vegetable, forage, litter management system; and (4) demonstrate litter management practices on grower owned land under grower conditions.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.