Nutrient cycling in grazing systems.

Abstract

This research was conducted at the University of KwaZulu-Natal, Pietermaritzburg, South Africa. The research encompasses five different studies to assess nutrient cycling in intensive and extensive grazing systems with a view to optimising livestock production. The first study was designed to assess the effect of teff-lucerne mixtures on teff, lucerne and teff-lucerne mixture yields. Lucerne and teff-lucerne mixtures benefited from the association. The overall soil N content of the teff-lucerne mixture plots was greater than the teff alone plots. The second study focused on teff-leucaena association evaluation. It had two leucaena plant row spacings as treatments, 180cm and 120cm, respectively. Teff grown in mixture with leucaena produced a total teff dry matter (DM) of 7931.57 kg ha¯¹ for the 180cm row spacing and 8329.57 for the 120cm row spacing compared to the 3548.93 kg ha¯¹ of DM obtained from the teff alone treatment. The teff-Ieucaena stand also had a greater DM yield response to leucaena row spacing compared to the teff alone. In terms of nutritive quality, all stands from the teff-leucaena plots were better than the quality obtained from the teff alone plots. Total N content of teff from the l80cm row spacing was 21.83 g kg¯¹ and that from the 120cm 16.07 g kg¯¹ compared to the total nitrogen (N) content of 19.77 g kg¯¹ of the teff alone treatment. The total phosphorus (P) content was 2.73, 1.96 and 2.07 g kg¯¹ for the 180cm, 120cm and teff alone treatments respectively. However, the total soil N content was higher for the teff alone plot than for the teff-leucaena plots, which are 1.91, 1.48 and 100 g kg¯¹ for the teff alone, 180cm and 120cm treatments respectively. The third study was designed to assess the effects of different N fertilizer application rates on teff yield response. The rates applied were 0, 50, 100 and 150 kg N ha¯¹. There was significant difference in teff response of the three N fertilizer application rates compared to the control and teff DM yield response was lower for the 150 kg N ha¯¹ (838 kg ha¯¹) treatment compared to the control (553 kg ha¯¹). Both teff DM and nutritive value were higher in the plots treated with N fertilizer than in the plot which received no N fertilizer (control). The soil N content was also higher in those plots treated with N fertilizer. Study four was conducted on the Department of Grassland Science's grassland management techniques trial field at Ukulinga. The effects of nutrient cycling under different management techniques such as burning, mowing and grazing on grass yield response, plant quality and soil nutrients were assessed. However, the response of grass DM yield and P content was not significant but the three treatments had a significant effect on grass N content. Their effect on soil N content was also significant and the grazing plot had the greatest soil N levels. The last study was conducted in the rural areas of Okhombe and Zwelitsha to assess the effects of grazing intensity on grass yield response, plant quality and soil nutrient status at different distances from homesteads. Grass DM yield and nutritive value declined when distance from the homestead increased. The soil N content also was higher nearer to the homestead than further away. Most farmers, particularly in developing countries including those in Eritrea, often experience that their animals prefer forages from some plants such as lucerne, leucaena, and other indigenous leguminous plants. They also observe that they get greater yield from crops grown near leguminous plants or in rotation with legumes. They are also still using manure from their animals to fertilize their croplands. Therefore, it is still the duty of the researchers to demonstrate to farmers on farm studies to convince farmers that it is because leguminous plants have the ability to add quality and quantity to the feed of the animals and soil nutrients to the croplands. Hopefully, this study will convey to farmers the use of growing integrated grassllegume pastures and crops, and illustrate that livestock have their own role in transporting nutrients and hence use them as good means of distributors of soil nutrients.