Reconciling scientific approaches for organic farming research: Part II - Effects of manure types and white clover (Trifolium repens) cultivars on the productivity of grass-clover mixtures grown on a humid sandy soil

Summary

This Part describes the agronomic results of the multidisciplinary grassland study. This project concerned the effects of clover varieties and spring applications of animal manure on the yield of grass-white clover mixtures on a moist sandy soil (1993-1996). To be aware of the context of the findings in a multidisciplinary approach, attention was paid to: chemical soil fertility, damage to clover by slugs and soil borne nematodes. To increase the understanding of soil fertility, earthworm dynamics were also measured. At the end of the period the botanical composition of all plots was assessed. Factors measured besides total yield and clover yield were N, P and K yield. It was found that these ‘context ’-measurements were important for the overall explanation of the scientific results. Data were used for modelling several relationships between yield
parameters. The overall findings of this project led to an understanding and description of the main aspects of manure with regard to grass-white clover growth on a moist sandy soil.
It was concluded that on a moist sandy soil the amount of inorganic and organic N, the N
release and the K input were the main manure factors relating to fluctuations in total yields on white clover development and on N yields in the first six years after sward establishment. The inorganic N component in manure can be used strategically to improve the growth of the herbage in spring. Maintenance of soil fertility in terms of P, K and Ca levels is an important key factor for a successful organic grass-clover sward. Carbon rich FYM derived from a deep litter stable and composted before application increased the earthworm population, reduced the number of nematodes and maintained the highest level of soil pH, all factors which might positively affect white clover growth in the long term. FYM applied in spring resulted in the typical extended growth season in the second part of the growing season. On a sandy soil the high concentration of K in the FYM positively affects the potential white clover growth.
The choice of a persistent white clover cultivar is another important factor affecting herbage and N yields of an organic grass-clover sward. However, winter losses were not found to be the main cause of white clover reductions over the years. Losses in the growing season were related to slugs which reduced white clover leaf area. The literature shows that the cyanide concentration in DM herbage affects the susceptibility of white clover to pests.