1992 Annual Report for LS92-048
Developing Environmentally Sound Poultry Litter Management Practices for Sustainable Cropping Systems
Summary
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.
Objectives
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 economic litter management practices on grower-owned land under grower conditions.
Approach and Results
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 preplant or half preplant 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 six inches 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 one foot 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 one foot but does increase Ca at depths below three feet. 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 six inches 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 one foot. 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 one foot.
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 one foot 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/A. 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.
Impact
Results of this study indicate a significant impact to sustainable agriculture. Poultry litter has been shown to be an excellent source of nutrients for crop production. If rates of litter are applied according to soil test results and litter nutrient content, yields can be maximized and environmental problems such as NO3-N leaching and accumulation minimized.
Including cover crops in a vegetable production system has a positive effect on reducing NO3-N accumulation and leaching, thus reducing the incidence of ground water pollution. A systems approach of using cover crops in a vegetable production program reduces the risk of contamination of surface water and ground water by NO3-N.
The information gained from this study will be beneficial to producers by helping them develop management plans that will qualify for Best Management Practices. Poultry producers will benefit by enabling them to dispose of a larger amount of waste product with less environmental impact.
There was one aspect that emerged from this study that could create a problem with the use of poultry litter as a fertilizer source. Regardless of litter rate applied or cropping system used, residual soil P continued to increase. This was most pronounced in the surface 0-15 cm (0-6 in) of soil. This is the zone most susceptible to runoff, thus increasing the risk of non-point source pollution of surface water.
Legumes are able to use significant amounts of P. An advantage of using legumes for removing excess P is that no additional N fertilizer has to be applied since legumes can obtain N from the atmosphere through N2 fixation. A study was initiated this spring (1995) to evaluate the use of warm- and cool-season legumes in rotational vegetable cropping systems to remove excess P supplied by poultry litter.
December 1995.