Mulberry production with swine lagoon effluent

T.O. Ramos, L.P.E. Lara, L.J.A. Rivera & G.J.R. Sanginés
Instituto Tecnológico Agropecuario No. 2, Conkal, Yucatán, México.

INTRODUCTION

In sustainable animal production systems, the procedures for nutrient management to enhance environmental conditions have always been a well-recognized priority. The advent of concentrated, large animal production units presents the monumental challenge of responsible management of manure nutrients (Adeola, 1999). Swine manure is primarily a mixture of urine and faeces, and it contains undigested dietary components, endogenous end- products and indigenous bacteria from the lower intestinal tract (Sutton et al., 1999). On average, 60 to 80 percent of ingested N and P are excreted, while for K it is over 90 percent (Voermans, Verdoes and den Hartog, 1994). Swine waste from anaerobic lagoons contains virtually all of the nutrients needed for plant growth and development. This represents a valuable resource that can replace costly inputs in pasture and crop production (Mueller et al., 1994), and with appropriate application rates, potential soil and water pollution is eliminated (Sutton et al., 1978). The application of lagoon effluent to land is facilitated with crops that assimilate large amounts of nutrients.

The Yucatán peninsula is located in southeast Mexico. Geologically, the northern part of the peninsula may be characterized as a Cenozoic carbonate platform, with extremely permeable carbonate rocks, that consists of an undulating karst plain with gentle slopes from sea level to an elevation of 30 m. The insoluble fraction of limestones produce the soils of Yucatán. They are thin, residual, terra rossa soils, commonly rich in the mineral halloysite. Soils rarely exceed a few centimetres, and most of the terrain consists of bedrock outcrops with thin accumulations of soil in topographic lows. The high surface infiltration and rock permeability, and the low relief of the area combine to produce a regional aquifer with a very low hydrologic gradient (Dohering and Butler, 1974).

The only natural source of fresh water in the Yucatán peninsula is a fragile aquifer system consisting of a fresh water lens floating on saline water, and the great vulnerability of the aquifer is revealed in studies related to water pollution in wells (deeper than 30 m) in the city of Mérida, with faecal coliform bacteria exceeding the maximum permissible levels for treatment to produce a safe water supply (Vázquez & Manjarres, 1993; BGS, FIUADY, CNA, 1995).

Swine production in Yucatan is economically important. Its value was over US$100 million in 1999. The pig population has been growing dramatically since 1975 has increased more than 20 percent annually between 1990 and 1997 (INEGI, 1998). Although swine production has been transformed into a dynamic activity, soil and water pollution can occur whenever large quantities of organic waste materials are concentrated in a single area and soluble materials move downwards into the groundwater. Nitrate concentration in wells near swine farms reaches high levels, of more than 45 mg/l (Pacheco, Cabrera and Gómez, 1997). On the other hand, phosphorus does not yet represent a pollution risk, because of its lower soil mobility than that of nitrate-N (Coffey, 1999) and it is adsorbed in limestone (Pacheco and Cabrera, 1996).

Mulberry demands a lot of nutrients in order to produce large biomass yields with high nutritional value. The maintenance of soil fertility and plant persistence become important if significant amounts of soil nutrients are to be extracted in the biomass under cut-and-carry systems (Sánchez, 2000). There is also a close relationship between fertilizer dosage and quantity/quality of mulberry leaves (Ye, 2000). Therefore, mulberry represents an alternative to applying nutrient-rich swine lagoon effluent and to decreasing the environmental impact of intensive swine production.

MATERIAL AND METHODS

The study was conducted at the Instituto Tecnológico Agropecuario No. 2, located near Conkal (Yucatán, Mexico). The experimental site is located at 9 m above sea level in a tropical (Aw 0) climate with annual rainfall ranging from 900 to 1 000 mm. Average temperature is 26.5ºC (García, 1981). Soils are calcareous, rocky and shallow and are classified as leptosol rendzic (FAO, 1998), with a medium depth of 15 cm.

Stakes measuring 30-40 cm, with at least four buds, were directly planted. Rooting was induced with indol 3-butyric acid.

The experimental design was a complete randomized block in a split-plot arrangement with four replicates (Table 1). The main plot was density (10 000 and 20 000 plants/ha), and subplots were level and type of nitrogen application; including a control (T₀) no nutrient addition; urea (U) at 300 kg of N/ha/year, in four applications (every 91 days); and effluent loading rates (ELR) from an anaerobic lagoon (10 m in diameter by 2.5 m in depth) to apply approximately 150, 300 and 450 kg of N/ha/year in ten applications (every 35 days) with a pump for solids. The experimental plot measured 5 x 5 m and the useful plot 4 x 4 m. Cuts were every 91 days beginning on 15 July, 1998.

TABLE 1

Description of treatments

Treatment	Density Plants/ha	Nitrogen level kg/ha/y	Fertilization type
1	10 000	0	None
2	10 000	300	Urea (U)
3	10 000	150	Swine lagoon effluent (SLE 150)
4	10 000	300	Swine lagoon effluent (SLE 300)
5	10 000	450	Swine lagoon effluent (SLE 450)
6	20 000	0	None
7	20 000	300	Urea (U)
8	20 000	150	Swine lagoon effluent (SLE 150)
9	20 000	300	Swine lagoon effluent (SLE 300)
10	20 000	450	Swine lagoon effluent (SLE 450)

Forage production and nutritive value were determined. Forage samples were used to evaluate DM production from the whole plant. The proportion of leaves, young stems and mature stems were determined from two plants in every experimental plot. DM, CP and OM were determined by AOAC (1980). NDF was determined following Goering and Van Soest (1970). Sample preparation for Ca, Mg and K was according to Fick et al. (1979) and concentration was measured in an atomic absorption spectrophotometer (GBC 901). P concentration was evaluated according to Harris and Popat (1954) in a ultraviolet light spectrophotometer (Spectronic 21). Nitrogen recovery was calculated by subtracting amounts taken up in the control treatment and dividing by the amount of nitrogen applied (Kelling et al., 1977). When data effects were significant (P < 0.05), means were separated by using the Tukey test option of the ANOVA procedure of SAS for Windows v. 6.11 (1996).

RESULTS AND DISCUSSION

There was no density x N level interaction (P > 0.10) in DM production and its fractions. Therefore, only the principal effects are discussed. Total biomass yield was significantly increased (P < 0.01) with density, of 20.3 and 25.7 tonnes DM/ha for low and high density, respectively. This increase represents 26.6 percent more DM yield. These results are in agreement with Benavides, Borrel and Esnaola. (1986) who found that DM yield was increased when plant density per ha was higher. DM yield was significantly different (P < 0.01) among applications of urea and ELR compared with the control treatment. However, no significant yield difference was found between urea and ELR. Thus, N in the swine lagoon effluent was as effective as urea for forage production. Regression analysis shower a linear trend (P < 0.01) of total forage yield with increasing application rates of lagoon effluent. The linear equation, fitted to the control treatment and the three ELR treatments, was Y = 17.32 + 0.021 x, R2 = 0.356 where Y = total DM yield (tonnes/ha) and x = effluent N application rate (kg/ha). The 450 kg N/ha ELR produced the greatest DM yield, but it was not statistically different (15.7, 22.9, 26.0 and 26.8 tonnes/ha/year for 0, 150, 300 and 450 kg N/ha/year, respectively.

Swine lagoon effluent has been shown to be an effective nutrient source and can replace commercial fertilizer. Goat manure applied to mulberry in Costa Rica increased DM yield linearly (Benavides et al., 1994) and yield was higher when N was applied in the form of manure in comparison with fertilizer (Takahashi and Kronka, 1968). In agreement with this, DM yield in the present work was significantly different (P < 0.01) with 300 kg N as urea compared to 300 kg N as ELR (23.4 against 26.1 tonnes/ha/year, respectively).

Leaf: stem proportion (49.2: 50.8) did not change among planting densities and nitrogen level, despite yield differences. Leaf DM yield was significantly different (P < 0.01) among densities, 7.4 against 9.9 tonnes/ha/year. Leaf proportion decreased linearly with harvest length (Boschini, 2000).

Mineral concentrations of mulberry leaves are given in Table 2. No effects were observed (P > 0.05) on NDF (mean of 23.4), OM (mean of 87.1) and Ca (mean of 4.3 percent). Liu et al. (2000) observed higher NDF values in mulberry leaves cutting in spring and autumn, with 38.8 and 41.4 percent, respectively. Kitahara, Shibata and Nishida, (2000) reported lower Ca level (2.98 percent). There was a density x nitrogen level interaction in P concentration in leaves. Mg and K content were significantly affected (P < 0.001) by N fertilization form and level.

TABLE 2

Mineral concentration on dry basis in mulberry leaves when fertilized with swine lagoon effluent

Plants/ha	N level kg/ha/y	N source	Ash %	Ca %	P %	Mg %	K %
10 000	0		13.2	3.9	0.35	0.49	1.52
10 000	300	Urea	13.0	4.1	0.29	0.56	1.41
10 000	150	ELR	12.9	4.4	0.29	0.61	1.24
10 000	300	ELR	13.2	4.5	0.28	0.58	1.44
10 000	450	ELR	13.2	4.3	0.29	0.62	1.43
20 000	0		12.5	4.4	0.29	0.49	1.47
20 000	300	Urea	12.1	4.1	0.24	0.59	1.20
20 000	150	ELR	13.2	4.5	0.30	0.59	1.35
20 000	300	ELR	12.0	4.3	0.27	0.57	1.51
20 000	450	ELR	12.6	4.6	0.28	0.59	1.28
Density			0.0473	0.2342	0.0110	0.4762	0.0697
N level			0.3848	0.2226	0.0071	0.0001	0.0001
Density x N level			0.3897	0.3953	0.1134	0.4994	0.0027
Standard error			0.301	0.182	0.014	0.017	0.042

ELR = effluent loading rates.

Table 3 shows nutrient recovery by mulberry plants. These recoveries were affected (P < 0.01) by density and N level. Nitrogen uptake by the crop is important when land application is used as a wastewater treatment system because N is removed from the soil. Thereby preventing NO₃-N leaching to groundwater (Liu et al., 1997).

TABLE 3

Total nutrient uptake and recovery in mulberry as affected by N source and rate of swine lagoon effluent application

Density plants/ha	N level kg/ha/year	N source	N kg	Ca kg	P kg	Mg Kg	K kg
10 000	0		140.0	270.5	25.7	34.4	109.2
10 000	300	Urea	259.8	458.0	32.7	62.1	165.4
10 000	150	ELR	212.0	411.6	28.3	57.6	113.1
10 000	300	ELR	267.5	501.1	31.8	64.3	186.4
10 000	450	ELR	303.2	478.1	33.4	69.0	183.5
20 000	0		165.5	361.3	24.1	40.4	113.6
20 000	300	Urea	286.6	517.0	31.1	74.2	176.9
20 000	150	ELR	300.8	562.2	38.6	74.2	206.3
20 000	300	ELR	337.4	618.5	39.6	80.8	195.3
20 000	450	ELR	402.5	695.9	43.3	88.2	225.1
Density			0.0033	0.0011	0.0401	0.0044	0.0154
N level			0.0001	0.0004	0.0133	0.0001	0.0007
Density x N level			0.6380	0.6558	0.2727	0.8977	0.1531
Standard error			30.385	54.967	3.649	7.144	19.504

ELR = effluent loading rates.

Mulberry removed large quantities of the nutrients applied in the effluent. Removal per hectare increased with higher loading rates, resulting from both higher DM yields and higher concentrations in dry matter. The application of effluent to deliver the equivalent to approximately 450 of N/ha/year, did not cause agronomic problems and represents an alternative to diminish ambient concerns about swine production.

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