PROJECT RESULTS

In-Crop Application of Liquid Hog Manure in Irrigated Potato Production

Table of Contents:

• Background and Objectives
• Procedure and Project Activities
• Results and Discussion
• Conclusions

ARDI Project:

Total Approved:

Date Approved:

Project Status:

#98-102

$36,000

May 20, 1998

Completed February, 2001

Background and Objectives:

Manitoba produced over 4 million hogs in 1998, up 15% from the previous year, with the trend toward larger hog barns. Strategies for waste disposal need to be an integral part of management of hog operations. The high volume of liquid waste associated with hog operations, combined with the high costs of liquid waste transport highlight the need to identify approaches to waste disposal that maximize efficiency both of nutrient use and transport.

Application of swine manure on potatoes affords distinct advantages to both the hog and potato producer. Potatoes are a high value crop that require large nutrient inputs to achieve maximum production. To the hog producer, manure is the cost of doing business. A heavy user of the waste product of the hog industry would be of considerable benefit. And unlike cattle manure, swine manure does not appear to cause scab lesions.

Fall manure application raises serious concerns related to odour production, and volatile and leaching losses. Nitrate leaching could be particularly serious on the light-textured soils that are ideal for potato production.  There are, as yet, no adequately explored alternatives to fall swine manure application on potato soils.

In this study we explored the use of in-crop soil injection of swine manure on potatoes prior to canopy closure as an alternative to fall manure application. The advantages to this approach are 1) it provides the crop with nutrients at a time when nutrient demand is rapidly increasing, 2) it reduces the losses of N due to volatilization and leaching, 3) it minimizes the spread of the odour to at or near ground level, and below the canopy.

The objective of the project is to determine the effect of in-crop injection of liquid swine manure on potato yield and quality.

Procedure and Project Activities:

The project was conducted during the 1999 and 2000 field seasons. The study was carried out at two sites:

Experimental plots, 6.0 m wide x 10.0 m long, were laid out for Russet Burbank potatoes, according to a randomized complete block experimental design with 7 treatments, 4 replicates per treatment. The treatments are shown in Table 1. All fertilizer was applied prior to planting based on soil test recommendation, except for plots that were to receive manure or commercial fertilizer after planting. Phosphorus, potassium and sulfur were applied to achieve a final rate of (kg / ha): 134 P, 180 K and 34 S in the top 30 cm of soil. Actual amounts of fertilizer applied were adjusted to reflect the nutrient concentration in each manure treatment.

In 1999, plots were sown on June 2. In 2000, plots were sown May 23. Treated seed pieces were planted using a four-row commercial potato planter with a between-row spacing of 0.95 m and an in-row spacing of 0.38 m. Liquid swine manure was applied to the center three rows using a customized liquid manure injector with a 260 mm wide sweep. Manure was injected between potato rows to achieve manure N rates of 0, 50, 150 and 200 kg / ha. In 1999 manure was injected on July 12, 40 days after planting. In 2000 manure was applied July 10, 47 days after planting. These dates corresponded to five days after the first hilling operation, and approximately 10 days before full canopy closure. Commercial fertilizer N was applied, according to treatment protocol, as an in-crop treatment in liquid form between the hills by hand on the same day as manure was applied.

Table 1. Rate of N applied as swine manure or commercial fertilizer (kg/ha)

Measurements

Plants were destructively sampled from two-meter rows outside of the center two rows final harvest area for 1) above-ground biomass, 2) tuber number and 3) tuber mass, according to size. Leaf petiole samples for nitrate-N content to be taken at mid and late tuber bulking stages, and in 2000 at early- and mid-tuber bulking. Tubers from the center two rows of each plot were harvested, weighed and graded according to size classification, and assessed for quality based on shape, specific gravity, external blemishes, and incidence of physiological disorders. In 1999, tubers were graded for diseases between 16 and 21 weeks of storage. Coliform bacteria residual on the tubers after harvest were assessed by a rinse test.

Statistical Analysis

Data for each date and study site were analyzed separately. For each variable measured, data were analyzed by a one-way anova using PROC GLM of SAS software (SAS Institute Inc. 1990), to obtain analysis of variance, least square means, and standard error of the means.

Results and Discussion:

Potatoes that received swine manure at hilling yielded similarly to potatoes receiving 200 kg ha' commercial fertilizer at planting (Figure 1). Marketable yields were on average 64.5% of gross yields on the sandy soil, and 72.2 and 75.3% of gross yields on the 1999 and 2000 clay loam soils.

The timing of manure injection coincided with the onset of tuber initiation. It is therefore not unexpected that manure treatments might have a larger affect on early tuber development than on final yield, given this crop's capacity for compensatory growth. In 1999 on clay-loam soil, swine manure injected at the highest N rate ( 200 kg / ha N) significantly decreased tuber number in the two smallest size categories (1 - 3 and 3 - 5 cm) measured about two weeks after manure application. This translated into reduced tuber numbers in two of the larger size categories by late tuber bulking. Commercial fertilizer applied at the same time and rate had a similar effect at late tuber bulking. High N rates around the time of tuber initiation are known to delay tuber formation, particularly in the case of Russet Burbank. Fewer small tubers at early sampling suggest that tuber initiation was delayed at the highest N rates of manure or fertilizer. This did not occur at in-crop injection rates under 200 kg /ha N, indicating that it is probably safe to apply manure at hilling at rates up to 150 kg / ha N on clay-loam soil. On sandy soil, there was no indication of a delay in tuber development at even the highest N application rate. More rapid movement of water and nutrients away from the hill in the sandy soil may account for this greater tolerance to high N application at the time of tuber initiation.

Commercial fertilizer applied at hilling at the highest rate caused a similar decline in small­-to-medium grade tubers, indicating that the decrease in tuber number measured during early sampling was not due to manure, but I rather more likely, to an N-concentration effect.

Yields in both 1999 and 2000 were somewhat lower than the expected average for the region. This may have been due to the crop being planting two to three weeks later than normal for the region.

While potato is a crop sensitive to nitrogen deficiency, the lower yields observed in this trial were probably not related to insufficient N. Petiole nitrate values generally fell within the "adequate" nitrate-nitrogen range (800 - 1400 ppm in sap) for the mid-to-late-season crop development stage. Treatment effects on petiole N were not significant.

Tuber Disease

Tuber disease was low in both years of the study, though there was more evidence of diseased tubers in 2000 than in 1999. In 1999, the percentage of tubers rated "clean" ranged L, from 90 to 97% on the sandy site (Riverbend), and from 81 to 87.8% in tubers from the clay­ loam site (MCDC). Manure treatments in 1999 tended to have a higher disease incidence than the control and fertilizer treatments, though differences between treatments were small. In 2000, the percentage of clean tubers ranged from 58.5% to 67.5%. The cleanest tubers in 2000 were associated with the highest rate of manure application, while the most diseased were tubers from the next highest manure treatment. Results did not point to any consistent affect of manure on the incidence of any given tuber disease. Notably, rhizoctonia and scab, two diseases associated with animal waste, were not detected. The results suggest that a single year of exposure to swine manure is insufficient to increase or decrease disease severity in potatoes.

Potato Quality

While there was a greater incidence of tuber defects and tuber rot in clay loam than in sandy soil, there was no effect of manure treatments on these variables in 1999 or 2000 (Table 1).

Specific gravity was reduced in response to manure treatment in sandy soil, significantly so in  the case of the two highest manure rates (Treatments 3 and 4). By comparison, on clay-loam soil, specific gravities tended to be higher when manure or fertilizer was applied in-crop at the highest rate (Treatments 5 and 6). The potato processor requires a specific gravity of between 1.080 and 1.095 for frozen french fry processing.

Table 2. Effects of swine manure on the number of tuber defects (% of marketable yield), weight of rotten tubers (% marketable yield), and tuber specific gravity (g/cm') in sandy and clay-loam soil in 1999.

Human Pathogens

There were no fecal coliform bacteria present on the harvested tubers. From a food safety viewpoint this is a critical issue since the manure is applied to what will eventually become the product for human consumption. The soil environment does not present ideal conditions for the persistence of Fecal coliforms. The results suggest that the interval from tuber initiation to tuber harvest is of sufficient length to assure elimination of pathogens potentially harmful to human health.

Conclusions:

Following two seasons of study on clay-loam soil and on sandy soil, the results suggest few negative affects of in-crop manure injection on potato marketable yield or on potato quality. In the main, the effects of manure are the same as the effects of similar rates of commercial fertilizer applied at hilling.

Manure application at so late into the growing season raises legitimate concerns regarding possible risks of crop nutrient deficiency on the one hand, and crop nutrient excess, on the other. The results suggest that the demand for nitrogen by the crop during early establishment was not high enough to be affected by late manure or chemical fertilizer application. While manure injection at hilling may delay tuber initiation, the impact on final marketable yield was not significant.

A serious concern that of tuber disease, did not appear to be a problem after a single year of manure use.

These results, while encouraging, are inconclusive because of the short time-span of the study. There is a risk that tuber pathogens could become a problem upon repeated use of swine manure. Further work is necessary to support the findings of this study. Further work is also needed to determine the extent of movement of the N and P through the soil profile, when liquid manure is applied at rates of around 200 kg/ ha. In addition it will be important to monitor the longer-term effects on soil quality.

In the case of Russet Burbank, a high yielding late processing variety, fertilizer rates of at least 200 kg ha' of N are required for profitability. Input costs for fertilizer of $75 per acre represent the third highest cost next to seed and fungicide in potato production. Supplementation or complete replacement of commercial fertilizer with swine manure, which to date is without cost except for costs associated with transport and distribution, would be a significant saving to potato producers in proximity to hog barns.

Acknowledgements:

This project was made possible through funding from the Governments of Manitoba and Canada through the Canada-Manitoba Agri-Food Research and Development Initiative (ARDI).

Thanks also to the excellent technical assistance of Mr. Roger Fortier and Ms. Rhonda Thiessen.

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