[Estimation of the nitrogen fertilization needs of Brussels sprouts (Brassica oleracea var. gemmifera L.)]

The present thesis had as main objective to determine some parameters to be used in Brussels Sprouts nitrogen fertilization needs. The parameters are: harvest index, nitrogen internal requirement and nitrogen recovery from the fertilizer. Also the nitrogen fertilization effects in dehydration and conservation in post harvest sprouts were evaluated. The K and P internal requirements and its recovery from the fertilizer were estimated. The development of the crop was not affected by applications of these nutrients, due to the high soil natural fertilization. Testing crop was c.v. Lunet. Treatments consisted of different nitrogen rates (0-75-150-225 and 300 kg N/ha). Fertilization included phosphorus (92 kg P2O5/ha) and potassium (150 kg K2O/ha). Urea, CSP and potassium sulfate were used as sources of N, P and K. Maximum yield was obtained with 225 kg N/ha. Nitrogen also increased the production of total dry biomass. However, the ratio between sprouts dry biomass and total dry biomass remained constant with a value of 0.214. This is the harvest index. Nitrogen rates appeared to increase yields by increasing the number of sprouts rather than their size, using as maturity harvest index its size. Total areal absorption of nitrogen allowed to determine the average nitrogen concentration in the crop, this is, the internal requirement of N. The value obtained was 2.38%. The total nitrogen absorbed from the control treatment (without N) and the total N in the treatment with 150 kg/ha allowed to estimate N recovery finding a value of 40%. Using the mentioned parameters, it was possible to build a N recommendation table assuming different soil N supplies and different N requirement from the crop according to different potential yields. Finally, during post harvest sprouts were significantly affected in the decrease of their loss of weight, by rates of nitrogen over 75 kg/ha, that is, taking into account that uniformity is not necessarily considered in the harvest's state of maturity, as is the size of the sprouts, which doesn't imply the same state of development of each one of them, making this point questionable