The Impact of Biointensive Cropping on Yields and Nutrient Contents of Collard Greens in Kenya.
Gatua W. Mbugwa1, Erick C.M. Fernandes2, Max J. Pfeffer2, and Eloy Rodriguez2. (1) Univ of Wyoming, Plant Sciences Dept 3354, 1000 E University Avenue, Laramie, WY 82071, (2) Cornell Univ, Dept of Crop and Soil Sciences, Ithaca, NY 14853
A study was conducted in Kitale, Kenya, to compare yields of collard greens (Brassica oleracea var. acephala) of both biointensive and conventional cropping. Soil and plant nutrient dynamics in the two cropping systems, nutrient transport, and potential sustainability of biointensive agriculture were evaluated. This field study was a 2 X 2 X 2 factorial experiment in a randomized complete block design. The three factors were digging, spacing, and natural pesticides. There were a total of three experiments with eight treatments each in two seasons (Experiment 1-3). Crops of Experiment One and Experiment Two were grown in the first season. Experiment Three crop was grown in the second season. Biointensive spacing was found to have significantly greater collard yields than conventional spacing in all three experiments. There was a significant interaction between double digging and biointensive spacing in Experiment Two that resulted in higher yields. In the second season, double digging had greater yields than single digging, but significance was at a lower alpha of 0.10. The greater yields in the second season suggested that the beneficial effects of double digging increased with time. Natural pesticides did not increase yield and may have had adverse effects. In Experiment Two, beds with pesticides had lower yields than beds without pesticides, but at a lower alpha of 0.10. Soil macronutrients, except Nitrate and Magnesium, increased after cropping. This increase was attributed to the manure used. Soil Nitrate was significantly less in biointensively spaced beds after cropping. Magnesium was significantly less in double dug beds after cropping. This showed that the greater yields attained by biointensively spaced beds and by double dug beds came with some minor cost to the soil. Double digging may have increased leaching of magnesium from the topsoil. Accumulated C and accumulated N in collard leaves were significantly greater for biointensive spacing than for conventional spacing for all the three experiments. Percent C and percent N in plant tissue (Experiment Three) were significantly higher in biointensively spaced beds than in conventionally spaced beds suggesting some symbiotic N fixation and increased C under intensive cropping conditions. A concomitant increase in both percent C and percent N in collard tissue is consistent with increased protein content. It was therefore concluded that biointensively spaced collards had more protein content than conventionally spaced collards. Keywords: Biointensive agriculture, collard greens, conventional spacing, double digging, Kenya, macronutrients, micronutrients, single digging, sustainable agriculture.