Element composition and quality of lettuce (Lactuca sativa var. Biweri), grown with sheep-manure composts
Radics, L.; Pusztai, P1, Biró, B.; Biró, Zs.1; Németh, T.2, Monori, I.
Key words: compost, manure, phosphorus, nitrogen, lettuce
Abstract
Two representative Hungarian soil-types (slightly humus sandy and loamy saline) were used to study the effect of various compost-products, made from sheep-yard manure and phosphorous amendments on the biomass-production of lettuce (Lactuca sativa var. Biweri) in a pot-experiment. Two types of phosphorous amendments, such as raw-phosphate with high- or a phosphorous rock with low solubility were used as amendments during the twelve-week composting process. Pots of five-hundred g weight were used and considering the ecophysiological demand of the lettuce, low (30 t/ha) optimum (60 t/ha) and provocative (120 t/ha) levels of manure compost were applied to the soils. Yield of lettuce and mineral content analysis were done by ICP and soil-analysis by TVG. Statistical differences were shown (LSD5%) following ANOVA. An increasing yield of lettuce was recorded simultaneously by the compost doses up to the provocative level at both soil-types. Effect of composts was found to be the best at the low-fertility sandy soil with slight humus content. Among the compost-types, the low-releasing-phosphorous-rock was the most appropriate also on the sandy soil. Summarizing the results, sheep-manure-composts could be the prospective amendments for the low-fertility soils.
Introduction
It is common to improve the soil fertility with different types of artificial and natural fertilisers in the farming practice (Biró et al. 2005). Composting has become an everyday routine in manure treatments nowadays to keep the original nutrient value, improve the physical characteristic and to speed up the biological degradation, while reducing the nitrate-nitrogen losses (Füleky, 1999).
It is expected that composts enriched with different amendments can provide advantages (ie. higher yields) or disadvantages because of some plant chemical ingredients (e.g. higher nitrate content) depending of the actual type of the compost, dosage and not least of the soil type. Our experiment was targeted on getting information on these parameters. Typical Hungarian soil types were selected and used for the test with different dosage of sheep manure based compost mixed and amended with different substances. All the rules of organic farming regulation were strictly kept when the amendments, manure and management were selected (Radics, 2001).
Materials and methods
Two representative, but in their main characteristic different Hungarian soil-types (low humus sandy soil and loamy saline one) were used to study the effect of various compost-products. Sheep manure was composted for 3 month. This compost was completed with phosphorous amendments to measure the effect of different compost mixtures on the biomass-production of the lettuce in a pot-experiment.
Originally the research involved nine compost types. We’ve also examined the effect of some compost types, which were ameliorated with selected phosphates. Phosphorus is one of the most crucial nutrients in the soil because of its low availability. During the composting process we used a highly soluble raw-phosphate (K4) and a high phosphorous content rock (K7) of low solubility (Zapata, 2004). The added phosphate provided more continuous nutrient supply. The particular amount, the mixture content and the technology itself are under procedures for obtaining patent protection, so that it is not public yet. Two controls were used: sheep manure compost with zero P amendment (K1) and pure soil without any compost as null control (K0). After completing the compost mixtures, soil and compost samples were dried, ground and filled into the pots. To find the optimal amount of compost three different doses were tested according to the needs of lettuce as it was cited in literature. Low level was 30 t/ha equivalent, optimum level was 60 t/ha equivalent and provocative level was 120 t/ha equivalent dosage. The total weight of soil and compost sample mixture was 500g in pots and was placed in a light room (Penning, 1989).Fresh weight of shoots, length and width of leaves of lettuce were measured after 10 weeks and dried to a constant weight on 65 °C before the plant nutrient content was analysed (ICP). Soil samples were scrutinized with standardised general and full analyses (TVG**). Data were analysed by one-way ANOVA with t-test.
Results
The total nitrogen content of lettuce leaves is shown on Figure 1. 

Figure 1: Total nitrogen content in the leaves of lettuce on slightly humus sandy and (solid white) loamy saline soils (stripped) depending on different compost doses. Significant differences from zero phosphorus amendment (K1-x) are labelled with *.
Mineral content analyses of lettuce showed that the total nitrogen content of lettuce was practically equal on both examined soil types. Compared to the control treatment (pure sheep manure, K1) the highest dose showed significant difference in most cases.
But, on sandy soil plots, the treatment with medium dose compost with raw-phosphate amendments also gave significantly higher nitrogen content of lettuce.
Each treatment had significantly higher phosphorus content in lettuce leaves compared to the control treatment (no added phosphorus, K0) on sandy soil plots except the smallest dosage of phosphorous rock. The smallest dosage could only be significantly higher in raw phosphate amended mixture on saline soil plots. Phosphorous rock was more effective to provide nutrients for lettuce than raw phosphate.
Phosphorus content in the leaves of lettuce is shown on Figure 2. 

Figure 2: Phosphorus content in the leaves of lettuce on slightly humus sandy and (solid white) loamy saline soils (stripped) depending on different compost doses. Significant differences from zero phosphorus amendment (K1-x) are labelled with *.
The phosphorus content is significantly higher in lettuce leaves compared with the control treatment (K0) in almost all doses on sandy soil tests. The only exception was the smallest dose of phosphorous rock compost treatment.
Low-dose treatments could only have significant effects on plant phosphorus content if the treatment was raw-phosphate enriched compost in loamy saline soil test.
Comparing compost mixture varieties, phosphorous rock treatment effectively increased phosphorous content of lettuce. Presumably phosphorous with slow solubility is ideal because it provides steadier availability during the growing season. Increment of phosphorous content was less on loamy saline than on sandy soil, but differences were still well detectable. 

Discussion
Mineral content of lettuce strongly increased under high doses of compost on sandy soil. The total nitrogen content was 2-3 times higher in the lettuce leaves in these cases. This phenomenon indicates, that there is a potential risk of the nitrate-accumulation especially on sandy soil as it could be found in the literature (Biró et al. 2005, Fodor et al. 2006).
Changes of phosphorous content were similar to the ones of the nitrogen content. It was verified that phosphorous amended compost could provide more soluble phosphorous to the soil and to the crops compared with not treated compost.In the case of loamy saline soil, significant nitrogen-growth was also observable in the soil at the end of the growing season, but in the lettuce leaves only. The highest dose of both compost forms caused a significant difference. Accordingly, the risk of nitrate and nitrite uptake is lower compared to sandy soils. 
Summarising economical, environmental and food-quality aspects low and medium doses of compost seems to be expedient. When you determine doses at establishment of a new crop production system, basic physical, chemical and biological characteristics of the soil and quality of the applied compost should be considered too, as other authors referred it also (Radics, 2001; Seléndy, 1999; Füleky, 1999, Várallyay, 2002).
Conclusions
Summarizing the results, the sheep-manure-composts could be a promising amendments for the low-fertility soils and it is recommended to use as compost for lettuce. At the higher doses, however, beyond the optimal level for organic agricultural conditions, there could be a potential risk of nitrate-accumulation, which needs to be considered at the frequent application.
However, it is expected that the results are the same under field conditions, it is necessary to extend the experiment to outdoor trials to get information about the true effect in the circumstances of a farm production.
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