AdubaÃÃo orgÃnica da batata (Solanum tuberosum l.) com esterco e/ou Crotalaria juncea l. em um neossolo regolÃtico

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Potato (Solanum tuberosum L) is the main cash crop in the Agreste region of the state of ParaÃba in Northeastern Brazil. The main limiting factors of agricultural production in this region are the low amount and variable pattern of rainfall precipitation and the low fertility of the soils, particularly regarding N and P availability. Animal manure is practically the only nutrient source applied to soils during potato cultivation. However, the amount of manure available is usually not enough to fertilize the agricultural fields, due to the small size of most farms. Farmers often have to buy manure from other areas, which increases production costs. For this reason, the cultivation of Crotalaria juncea L. as a cover crop for incorporation into the soil was proposed as an alternative to replace or reduce the amounts of animal manure necessary for crop production and soil fertility maintenance. The objective of the first part of this study was to quantify potato productivity and evaluate the status of soil nutrient stocks throughout 5 years of manure and/or C. juncea incorporation to an Entisol in the Agreste region of ParaÃba. The study was conducted on field plots (6 x 10 m) from 1996 to 2002 (between 1997 and 1998, experiments were not conducted due to insufficient rainfall precipitation). Experimental treatments were: planting and incorporation of C. juncea during flowering (C); application of 15 t ha-1 of animal manure (E), planting and incorporation of C. juncea during flowering + application of 7.5 t ha-1 of animal manure (CE), control plots without C. juncea or animal manure (T). Soil nutrient levels and pH increased significantly in the treatments that received manure (E and CE) throughout the 5 years of the study, mostly for the treatment E. Even though the greatest increases in soil nutrients were observed in the treatment E, potato yields were greatest for the CE treatment. It was hypothesized that this occurred because the mineralization of nutrients was more synchronized with the demand of potato in the CE treatment. In order to test this hypothesis, field and glass-house experiments were conducted in 2003 and the dynamics of soil nutrient availability during the growing season of potato was evaluated. In the field experiment, the dynamics of residue weight and nutrient loss were evaluated. Samples of manure and plant biomass were placed into nylon screen bags and buried at 20 cm of depth. Every two weeks, one bag in each plot was removed, oven-dried, weighed, and the nutrient content was analyzed. Weight and nutrient losses were greater during the first month after incorporation for all treatments. At the end of the growing season, the proportion of the biomass and nutrients, which were incorporated and still remained in the bags, was greater for the treatments E and CE. This indicates that the decomposition of manure is relatively slower, compared to the plant biomass incorporated. The dynamics of soil nutrient availability was also evaluated in the field plots through bi-weekly soil sampling (0-20 cm) during the potato growing season. Extractable P and K were greater for treatments E and CE throughout the whole season. However, inorganic N (N-NO3- + N-NH4+) was lower in the treatments E and T, in comparison to treatments C and CE, during the initial period after incorporation, indicating that manure leads to N immobilization and may limit potato growth during the beginning of the growing season. In the green house experiment, the availability of nutrients in the soil from the field plots was evaluated by cultivating buffel grass in pots for three consecutive 35-day periods and measuring biomass production and nutrient uptake at each period. Buffel grass biomass production and nutrient uptake were greater for the treatment CE 35 days after planting. However, at 70 and 105 days after planting, biomass production and nutrient uptake was greater for treatment E, followed by CE, C and finally T. The results indicate that the combination of manure and C. juncea led to a more synchronized mineralization with the demand of potato, since it was able to supply enough P and K without causing deficiency of soil N through immobilization during early season. This is of particular importance for annual crops, which demand nutrients during its relatively short life growing cycle. The incorporation of manure may be more adequate for perennials crops, since the manure supplies enough P and K and releases N at slow rates, which may be enough for certain perennial plants. The cultivation and incorporation of C. juncea as green manure, without the addition of manure, may lead to soil nutrient depletion, particularly P and K, since the amount of these nutrients that are removed by harvest are exported from the system. The N fixation by C. juncea could even promote a priming effect and lead to depletion of native soil organic matter

ASSUNTO(S)

batatas engenharia nuclear adubaÃÃo organica esterco solanum tuerosum adubaÃÃo crotalaria juncea

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