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Title: Advances in nitrogen fertigation of citrus

Author
item Alva, Ashok
item MATTOS, DIRCEU - SYLVIO MOREIRA CITRUS RES
item QUAGGIO, JOSE - CENTRO DE SOLOS E RECURSO

Submitted to: Journal of Crop Improvement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2007
Publication Date: 2/2/2008
Citation: Alva, A.K., Mattos, D., Quaggio, J.A. 2008. Advances in nitrogen fertigation of citrus. Journal of Crop Improvement. 22:121-146.

Interpretive Summary: Application of nutrients with irrigation water is termed as “Fertigation”. Progress in micro irrigation technology, such as micro-sprinklers and/or drip irrigation contributed to increased adoption of fertigation technology. This technology facilitates application of nutrients with increased frequency with no or minimal cost for application. Furthermore, fertigation allows nutrients to be applied in small doses, when it is needed, and within the zone of maximum root distribution. The nutrient uptake efficiency is often greater as well as increased yield and crop quality with fertigation as compared to those with other methods of fertilizer application. In this paper, some general guidelines for fertilization of horticultural crops are discussed. Furthermore, responses of citrus trees (of different age, rootstock/scion combination and different production conditions) to fertigation verses broadcast application of dry granular fertilizer are discussed. A five-year demonstration study on a large commercial grove showed lower groundwater NO3-N concentrations with fertigation as compared to that of the grove which received similar N rate as broadcast application of dry granular fertilizer.

Technical Abstract: Advances in micro irrigation techniques, i.e. drip and under the tree sprinklers, have facilitated greater adoption of fertigation especially for perennial crops including citrus. It is generally believed that fertigation improves nutrient uptake efficiency, and increases the yield as well as crop quality as compared to those with conventional dry fertilizer broadcast application. Fertigation, as compared to the dry fertilizer broadcast application, is expected to minimize leaching of NO3-N below the root zone. The evaluation of tree response to changes in nutrient management requires long term studies because of large nutrient reserve in the woody portion of the trees. In this paper, we summarized the recent fertigation studies on horticultural crops, with main emphasis on citrus. Two year studies on newly planted citrus trees showed no significant difference between the fertigation and dry fertilizer broadcast treatments. This is in part due to relatively low nutrient demand during at least two years after planting. Conditioning the trees with different nutrient management programs since the planting and evaluation done during the seven and eight-year old trees showed significantly greater fruit yield with fertigation as compared to that with dry granular fertilizer broadcast application. The optimum N rate with continuous fertigation treatment was lower by 35 kg.ha-1 as compared with that for the dry fertilizer broadcast treatment. Six year study on twenty-plus year old ‘Hamlin’ orange trees on ‘Cleopatra mandarin’ rootstock showed no significant difference between the fertigation and dry fertilizer broadcast treatments. A five-year study on thirty-five plus year old ‘Valencia’ orange trees on ‘Rough lemon’ rootstock showed a significant decrease in surficial aquifer NO3-N concentration underneath a grove which received total fertigation as compared to that in a grove which received dry granular broadcast (3 appl/year) of similar N rates. In the former, the groundwater NO3-N concentrations were below the maximum contaminant limit (MCL) for drinking water quality standards of 10 mg.L-1, while those of the latter were above the NO3-N MCL throughout the duration of the study. Despite the positive effects observed on fruit yield of citrus trees in temperate growing conditions, soil acidification and consequently losses of Ca and Mg through the soil profile might be increased in tropical conditions because of localized application of nutrients. Therefore, careful management practice must be observed in order to maintain the sustainability of fertigated groves.