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POTASSIUM REQUIREMENTS FOR GARLIC UNDER FERTIGATION
Crop yields under fertigation have greater yield potential that previously imagined (Papadopoulos, 1987; Hartz, 1994; Castellanos et al., 2001a). This is due to optimized systems for supplying water (i.e. drip irrigation) and nutrients in a way that is practically permanent and includes optimum conditions of soil aeration. At these yield levels, demand for nutrients also increase well above those that normally occur in systems using gravity irrigation (Castellanos et al.,2001b). As crop yields increase, the amount of potassium (K) required also rises, as do demands for all other nutrients. The volume of K applied to garlic crop ranges from 60 to 150 kg K2O ha, depending on the level of K in the soil, crop nutrient absorption, target yields, and the characteristics of the soil itself. Three basic steps are involved in maximizing yields of garlic under fertigation:
1) Soil analysis,
2) Crop nutrient demand throughout the season, and
3) Most recently mature leaf (MRML) nutrient concentration references.
Of these three factors, the last two are not very well known in garlic. Potassium demand by garlic has been reported to range from 125 to 180 kg K2O/ha (Bertoni et al., 1988; Zink, 1963).
The present study was conducted in a Vertisol with a pH of 7.8 at the Celaya Agricultural Research Station of the National Institute of Agricultural Research (INIFAP); located in Central Mexico. The study consisted of two experiments, one conducted in 1997-1998 using furrow irrigation, and a second in 1998-1999 in which fertigation was used. Potassium extraction curves were obtained for both experiments, while a third experiment (also using fertigation) was established in 1999-2000 in order to explore the effects of plant density on yields and the amount of K extracted by garlic plants. In all three experiments, the crops received 80 kg of P2O5/ha at the time of planting. Figure 1 shows the amount of K extracted by the crop in both experiments.
Figure 1. Potassium extraction by garlic under different production levels in a Vertisol in Central Mexico.
In the furrow irrigation experiment, the final K2O extracted by the crop was 175 kg of K2O/ha (yield 19.1 ton/ha). In the fertigation experiment, the final extraction of K was 295 kg of K2O/ha (yield 29 ton/ha). On the basis of these data, one ton of garlic removed as much as 9.1 to 10.1 kg of K2O. Figure 2 shows the effects of plant density on crop yield and K extraction.
Figure 2. Bulb yield and potassium extraction (kg K2O extracted/ha) of garlic under fertigation for four different population densities.
As yields increased, bulbsize decreased, thus affecting the crop value on the fresh market. For industrial purposes, however, high population density is not a problem. Otherwise it is more convenient to use a plant density of 300 thousand plants/ha.
This research project was supported by PPI/PPIC in Mexico, and the field work was done by Dr. Javier Castellanos at the "El Bajio" INIFAP field research station. For more information, please contact the INPOFOS office.
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