I.Q. Ferreira

Response of stevia to nitrogen fertilization and harvesting regime in northeastern Portugal

ABSTRACT The adaptation of stevia to the growing conditions of NE Portugal is assessed, including the tolerance of this species to cold temperatures, and the potential to produce biomass when grown as an annual crop and when subjected to various nitrogen (N) rates and two harvesting regimes. Almost all the plants died during the winter of 2014 (minimum temperatures peaked at −8.0°C), making it necessary to replant the crop the following spring. With the best cutting regime (double cut) and N rate (150 kg N ha−1), 1514.4 and 2390.0 kg ha−1 of dry leaves were produced, respectively, in 2014 and 2015. Leaf chlorophyll concentrations estimated by the SPAD (Soil and Plant Analysis Development)-502 chlorophyll meter and a NDVI (Normalized Difference Vegetation Index) carried out by the Field Scout CM 1000 spectroradiometer showed significant differences among N rates, proving to be good indicators of plant N nutritional status. Based on the leaf analysis, provisional sufficiency ranges for N are proposed, namely 25–35 g kg−1 for mid-summer and 15–25 g kg−1 for early autumn. The fluorescence of chlorophyll a and the transient fluorescence intensity performed by the OS-30p+ fluorometer failed to show any stress induced by no-N control treatments in comparison to N-treated plants.

Management of Nitrogen-Rich Legume Cover Crops as Mulch in Traditional Olive Orchards

A low-input agricultural system needs a natural source of nitrogen (N). Legume species can fix great amounts of N that can be subsequently used by a nonlegume crop. In this study three legume cover crops were grown in traditional olive orchards in northeastern Portugal from October 2009 to May 2010, and the aboveground biomass was mechanically destroyed and left on the ground as a mulch. In the following growing season, from October 2010 to May 2011, two nitrophilic plant species were grown in circular microplots of 154 mm surrounded by polyvinyl chloride rings to assess the soil N availability. The N fixed by the legume cover crops, estimated by the difference technique, was shown to vary from 79.7 to 187.5 kg N ha−1. The nitrophilic plant species identified a small peak of soil available N in the autumn of 2010, probably resulting from the mineralization of the root system of the legume species. In the next spring, the increase of soil-available N in the plots where the legume cover crops had been grown, in comparison to the control plot, was residual. The great amounts of N present in the mulched materials seem to disappear without having entered the soil. Mulching with high-N content biomass may be troublesome due to the high risk of N losses probably by ammonia (NH3) volatilization.

Sufficiency ranges for lemon balm and nutrient removals in aboveground phytomass

ABSTRACT A set of fertilizer experiments were conducted during three growing seasons with the aim of establishing sufficiency ranges and crop nutrient removals for Melissa officinalis L. Critical nutrient concentrations were determined by the Cate–Nelson method or by removing 10% of extreme high and low values, respectively if a positive response to a given nutrient was recorded or not. Sufficiency ranges for macro, micronutrients, and SPAD-readings were set as: 27.0–40.0 g N kg−1; 0.8–2.7 g P kg−1 (May–August); 1.5–3.8 g P kg−1 (September–November); 10.0–25.0 g K kg−1 (May–August); 18.0–32.0 g K kg−1 (September–November); 5.0–25.0 g Ca kg−1; 3.5–8.5 g Mg kg−1; 18–125 mg B kg−1; 5–25 mg Cu kg−1; 75–500 mg Fe kg−1; 20–300 mg Zn kg−1; 30–250 g Mn kg−1; 30–45 SPAD-units. These results will allow laboratories to use plant analysis as an important tool in improving the fertilizer recommendations for this species.

Sufficiency ranges and crop nutrient removals for peppermint (Mentha X piperita L.) established from field and pot fertilizer experiments

ABSTRACT Peppermint is an important aromatic and medicinal plant used across the world in pharmaceutical, cosmetic and food industries. However, there is a lack of agronomic research on this crop which hinders the implementation of best agricultural practice at farm level. Plant analysis, for instance, cannot be used as a tool to implement a suitable fertilizer recommendation program, since sufficiency ranges and crop nutrient removals have not yet been established. Thus, the main objectives of the present work were to assess the response of peppermint to varying nitrogen (N), phosphorus (P), potassium (K) and boron (B) rates, to establish sufficiency ranges from macro, micronutrients and SPAD-readings and to estimate crop nutrient removals in the aboveground biomass. Field trials and pot experiments were conducted from 2013 to 2015 in a wide range of conditions involving 12 N, P, K or B fertilizer trials and a total of 48 cuts of biomass. Nitrogen fertilization increased dry matter yield of peppermint on the vast majority of sampling dates. In contrast, P, K, or B did not produce a significant effect on dry matter yield in any of the experiments. The sufficiency ranges set for macronutrients N, P, K, Ca and Mg are respectively 32.0 – 42.0, 1.2 – 4.5, 10.0 – 30.0, 7.0 – 23.0, and 4.0 – 10.0 g kg−1. Those for micronutrients B, copper (Cu), iron (Fe), zinc (Zn), and manganese (Mn) are respectively 20 – 200, 5 – 25, 100 – 600, 25 – 300, and 30 – 200 mg kg−1. Sufficiency range for SPAD-readings is 45 – 50 SPAD units. All these ranges were established for the commercial harvesting date. The amounts of N, P, K, calcium (Ca), and magnesium (Mg) removed in aboveground biomass are respectively 22.7, 1.6, 26.4, 16.4 and 4.8 kg Mg−1 of dry biomass.

Assessing the potential use of two portable chlorophyll meters in diagnosing the nutritional status of plants

ABSTRACT The SPAD-502 and the FieldScout CM 1000 chlorophyll meters were compared in their performance in diagnosing the nutritional status of plants. Leaves of a wide range of greenness were used to push the sensitivity of the tools to their limits. Both devices showed high reproducibility when used by different operators. The SPAD-readings were well-correlated with leaf nitrogen (N) concentrations, since leaves from heavily fertilized plants were not included in the sample population. The FieldScout-readings showed a marked saturation curve with the leaf N concentration, thus it cannot be used as a reliable N nutritional status index. The results also showed that the use of SPAD-502 in the diagnosis of the nutritional status of an orchard requires the establishment of specific critical concentrations for cultivars and sampling dates. The SPAD-502 appeared to have potential in the diagnosis of the nutritional status of the orchard for nutrients other than N.

The Effect of Legume Species Grown as Cover Crops in Olive Orchards on Soil Phosphorus Bioavailability

Some legume species are able to utilize phosphorus (P) from sparingly soluble P sources benefiting companion crops or those following in the rotation. Lupinus albus, Vicia villosa, and a mixture of eleven annual pasture legumes were used in olive orchards as mulched cover crops as a means of increasing the soil P availability. By soil testing and growing bioindicator P plants in the next season, it was possible to detect a slight but consistent increase in soil P availability. The results indicated that the increase in soil P availability was mainly due to the mineralization of the high P content legume residues, rather than the direct effect in the rhizosphere of the living plants. The results also suggested that the good adaptation of white lupine to low P environments might be due to a high internal P use efficiency of this species, producing high dry matter yields with low P concentration in their tissues.