Abstract
Information about nutrient extraction and exportation by crops, as well as the periods of highest nutrient demand is important for an adequate fertilization management. However, there are no studies on the nutrient uptake of short-stature hybrid castor bean. Therefore, the purpose of this study was to evaluate nutrient extraction and exportation by short-stature castor bean hybrid Lyra, in the spring-summer and fall-winter growing seasons. The experiments were conducted in the 2005/2006 spring-summer and 2006 fall-winter growing seasons on an Oxisol, in Botucatu, SP, in a randomized block design, with four replications. The plots consisted of plant samplings, which occurred 17, 31, 45, 59, 73, 97 and 120 days after emergence (DAE) in the spring-summer and 17, 31, 45, 59, 80, 100 and 120 DAE in fall-winter growing season. The growth of hybrid Lyra was slow and nutrient uptake lowest between emergence and the beginning of flowering. The period of highest dry matter (DM) accumulation rates and highest nutrient demand were observed 40 to 80 DAE, in both growing seasons. The order of nutrient extraction by the plants in the spring-summer growing season was: N>K>Ca>Mg>S>P>Fe>Mn>Zn>B>Cu>Mo. In fall-winter, S was more absorbed than Mg. Seed yield was higher in the spring-summer (2.995 kg ha-1), but nutrient extraction and exportation per ton of seed were similar in both growing seasons. Around 58 % of N and 84 % of P, and approximately half of the S and B absorbed throughout the cycle were exported with the seeds. However, most of the other nutrients accumulated in the plants returned to the soil in plant residues.
Highlights
For satisfactory yields of castor bean (Ricinus communis L.), the nutrient availability in the soil has to meet the crop requirements
In fall-winter, the dry matter (DM) accumulation increased until 100 days after emergence (DAE), when the accumulation rate became zero and the amount of DM remained stable until the end of the cycle (Figure 2)
I.e., in the fall-winter, the racemes showed higher DM accumulation rate between 50 and 80 DAE, in a shorter period than in spring-summer and at rates of 31.1 kg ha-1 day-1 only, which led to a reduced raceme growth and seed yield (Figure 2 and Table 1)
Summary
For satisfactory yields of castor bean (Ricinus communis L.), the nutrient availability in the soil has to meet the crop requirements. In a subsequent study, Nakagawa & Neptune (1971) found that the nutrient amounts absorbed by this oilseed crop throughout the crop cycle (133 days) were 156 kg ha-1 N, 5.3 kg ha-1 P, 172 kg ha-1 K, 13.8 kg ha-1 Ca and 12.5 kg ha-1 Mg, demonstrating the high nutrient demand during the growth and development of this crop. Aside from not taking the micronutrients into consideration, the said studies involved cultivars with a long growth cycle, medium height and non-uniform maturity, suited for manual harvest only. Since the production system of this oilseed crop has changed significantly with the development of new, short hybrids and cultivars, adequate for mechanized harvesting, with short growth cycle, high yield, uniform maturity and high oil content in seeds (Moro, 2008; Silva et al, 2010), further studies on the mineral nutrition of this crop plant are required. Since short hybrids have a high yield and short growth cycle, the nutrient demand concentrated in a short period is possibly much higher than of traditional cultivars, with long growth cycle and indeterminate growth
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