Development and production of iceberg lettuce irrigated with magnetically treated water

Irrigated agriculture has become a concern, given the scarcity of freshwater. To reduce its water consumption, new techniques and technologies have been proposed. Based on this, the objective of this work was to evaluate the influence of different soil water tensions at initiation of irrigation with magnetically treated water, on ‘iceberg’ lettuce Lucy Brown (Lactuca Sativa L.) development and production. The experiment was conducted in a greenhouse, using a completely randomized factorial design, to evaluate two water types (magnetically treated water – MW and ordinary water – OW) and four soil water tensions at initiation of irrigation (T1 – 15 kPa, T2 – 25 kPa, T3 – 40 kPa and T4 – 70 kPa), with three replicates. Tensiometers were used to estimate soil water tension. The evaluated parameters were: aerial part fresh and dry total mass; commercial head fresh and dry mass, root fresh and dry mass; stem fresh and dry mass; stem length and diameter; percentage of leaves with tip burn, total and commercial yield; water use efficiency related to total and commercial yield; plant exposed area; and dry matter content. Despite achieving greater water use efficiency, the magnetic treatment may have hindered the removal of water from the soil by the crop, especially at increased soil water tension at initiation of irrigation.

DESENVOLVIMENTO DE SENSOR DE UMIDADE DO SOLO UTILIZANDO O PRINCÍPIO DA RESISTÊNCIA ELÉTRICA

DESENVOLVIMENTO DE SENSOR DE UMIDADE DO SOLO UTILIZANDO O PRINCÍPIO DA RESISTÊNCIA ELÉTRICA FRANCISCO AÉCIO DE LIMA PEREIRA1; JOSÉ FRANCISMAR DE MEDEIROS2; NILDO DA SILVA DIAS2; FRANCISCO VANIES DA SILVA SÁ2; SUEDÊMIO DE LIMA SILVA3 E MIGUEL FERREIRA NETO2 1Departamento de Ciência e Tecnologia, Universidade Federal Rural do Semi-Árido, Campus Caraúbas, (Avenida Universitária Leto Fernandes, Sítio Esperança II, CEP: 59780-000, Caraúbas/RN – Brasil), [email protected]. 2Centro de Ciências Agrárias, Universidade Federal Rural do Semi-Árido, Campus Mossoró (Av. Francisco Mota, 572, Bairro Costa e Silva, CEP: 59.625-900, Mossoró/RN, Brasil), [email protected]; [email protected]; [email protected]; [email protected] 3Centro de Engenharias, Universidade Federal Rural do Semi-Árido, Campus Mossoró (Av. Francisco Mota, 572, Bairro Costa e Silva, CEP: 59.625-900, Mossoró/RN, Brasil), [email protected] 1 RESUMO A determinação do teor de água do solo é usada para decisões de manejo de irrigação. Com isso, objetivou-se avaliar tipos de eletrodos e materiais de enchimento e encapsulamento no desempenho de sensores de umidade do solo. Com base no princípio da resistência elétrica, diferentes sensores foram confeccionados e avaliados em um delineamento de blocos casualizados em esquema fatorial de 2 x 5, com dois eletrodos (20 x 5 e 15 x 5 mm) e cinco materiais de enchimento e encapsulamento (areia grossa + gesso com 30% pó de mármore, areia fina + gesso com 30% pó de mármore, lã de vidro + gesso com 30% pó de mármore, areia fina + gesso com 30% areia fina e areia grossa + gesso com 30% areia fina), com quatro repetições. Os resultados indicaram que os eletrodos de anéis concêntricos de tela de inox fixados com resina de poliéster mantêm uniforme as leituras de condutividade elétrica na medição da tensão da água no solo. Os eletrodos de 20 x 5 preenchidos com areia fina e encapsulado com gesso + pó de mármore foram mais sensíveis às baixas tensões e com leituras mais precisas da umidade do solo. Palavras-chave: agricultura de precisão, eficiência do uso da água, manejo da irrigação. PEREIRA, J. A. L; MEDEIROS, J. F.; DIAS, N. S.; SÁ, F. V. S.; SILVA, S. L.; FERREIRA NETO, M. DEVELOPMENT OF SOIL MOISTURE SENSOR USING THE PRINCIPLE OF ELECTRIC RESISTANCE 2 ABSTRACT The determination of soil water content is used for irrigation planning decisions. This study aimed to evaluate electrode types and filling and encapsulation materials on the performance of soil moisture sensors. Based on the principle of electric resistance, different sensors were made and evaluated in a randomized block design in a 2 x 5 factorial scheme with two electrodes (20 x 5 and 15 x 5 mm) and five filling and encapsulation materials (coarse sand + gypsum with 30% marble powder, 30% fine sand + 30% marble sand, 30% sand and gypsum with 30% sand) with four replicates. The results indicated that the concentric stainless steel mesh ring electrodes fixed with polyester resin keep the electrical conductivity readings uniform in the measurement of soil water tension. The 20 x 5 electrode filled with fine sand and encapsulated with gypsum + marble powder were more sensitive to low voltages and with more accurate readings of soil moisture. Keywords: precision agriculture, water use efficiency, irrigation management.

Analysis of soil oxygen dynamics as a diagnostic tool of the soil oxygen status in-situ

<p>Soil oxygen has been recognized as a potential limiting factor in plant production second only to water and nutrients. While it is widely accepted that soil gaseous oxygen levels below 10% V/V are detrimental to plant production, there are currently no accepted indices to quantify the effect of different agricultural practices on soil oxygen supply and availability. To address this challenge, a new approach is introduced, whereby indices describing the soil oxygen dynamics are determined using data from continuous in-situ soil oxygen measurements. To give the measurements a mechanistic interpretation, we developed a conceptual model describing the soil oxygen dynamics as a simplified mass balance between oxygen supply rate and oxygen consumption rate. The approach was applied to analyze field measurements of soil oxygen and water tension at 35 cm depth in avocado orchards irrigated with either Fresh Water (FW) or Treated Wastewater (TWW) in clay soil (~60% clay). The reliability of the method was shown, as soil respiration rates equivalent to 1-2 g O<sub>2</sub><sub></sub>m<sup>-2</sup> d<sup>-1</sup> were established, in line with previous reports for evergreen trees. The model defines the soil water tension at which oxygen supply to the measurement depth after irrigation surpasses the oxygen consumption rate as the critical soil water tension, and a value of ~50 mbar was established for the experiment site, again within the range described in the literature for soils with similar properties using other methodologies. Using the new approach, it was established that more hypoxic conditions occur in TWW irrigated plots as compared to FW irrigated plots due to a difference in the time required to reach the critical soil water tension – TWW irrigated plots took nearly 50% longer to reach a soil water tension of 50 mbar after each irrigation in the height of the irrigation season. This delay in TWW irrigated plots was directly related to the soil drying rate, which was lower in the TWW irrigated soils in both night and day periods, indicating both a hindering of drainage and of plant water uptake. In a second study site, the values describing the soil oxygen dynamics were found to relate to the soil stone content (particles>2mm), a known effector of soil aeration. By utilizing in-situ<sub></sub>measurements, the method aims to represent the intricate interrelations occurring in the field which may be missed using methods focusing on the individual factors affecting soil oxygen. The insights gained can provide the basis for designing management techniques to resolve unfavorable low oxygen levels in agriculture, as well as in natural environments where hypoxia affects soil carbon turnover, the evolution of greenhouse-gasses, and the fate of toxic elements in soils.</p>

Pigeonpea Yield and Water Use Efficiency: A Savior under Climate Change-Induced Water Stress

Frequent droughts have threatened the crop yields and livelihoods of many smallholder farmers in South Africa. Pigeonpea can be grown by farmers to mitigate the impacts of droughts caused by climate change. An experiment was conducted at Fountainhill Farm from January 2016 to December 2017. The trial examined grain yield in addition to water use efficiency (WUE) of pigeonpea intercropped with maize versus sole pigeonpea and maize. A randomized complete block design, replicated three times, was used. Soil water tension was measured at 20, 50, and 120 cm within plots. The highest and lowest soil water tension was recorded at 20 m and 120 m respectively. Combined biomass and grain yield were significantly different: pigeonpea + maize (5513 kg ha−1) > pigeonpea (3368 kg ha−1) > maize (2425 kg ha−1). A similar trend was observed for WUE and land equivalent ratio (LER), where pigeonpea + maize outperformed all sole cropping systems. The inclusion of pigeonpea in a traditional mono-cropping system is recommended for smallholder farmers due to greater WUE, LER and other associated benefits such as food, feed and soil fertility amelioration, and it can reduce the effects of droughts induced by climate change.

Peat depth as a control on moss water availability during drought

Peatlands are globally important long-term sinks of carbon, however there is concern that enhanced moss moisture stress due to climate change mediated drought will reduce moss productivity making these ecosystems vulnerable to carbon loss and associated long-term degradation. Peatlands are resilient to summer drought moss stress because of negative ecohydrological feedbacks that generally maintain a wet peat surface, but where feedbacks may be contingent on peat depth. We tested this ‘survival of the deepest’ hypothesis by examining water table position, near-surface moisture content, and soil water tension in peatlands that differ in size, peat depth, and catchment area during a summer drought. All shallow sites lost their WT (i.e. the groundwater well was dry) for considerable time during the drought period. Near-surface soil water tension increased dramatically at shallow sites following water table loss, increasing ~5–7.5× greater at shallow sites compared to deep sites. During a mid-summer drought intensive field survey we found that 60%–67% of plots at shallow sites exceeded a 100 mb tension threshold used to infer moss water stress. Unlike the shallow sites, tension typically did not exceed this 100 mb threshold at the deep sites. Using species dependent water content - chlorophyll fluorescence thresholds and relations between volumetric water content and water table depth, Monte Carlo simulations suggest that moss had nearly twice the likelihood of being stressed at shallow sites (0.38 ± 0.24) compared to deep sites (0.22 ± 0.18). This study provides evidence that mosses in shallow peatland may be particularly vulnerable to warmer and drier climates in the future, but where species composition may play an important role. We argue that a critical ‘threshold’ peat depth specific for different hydrogeological and hydroclimatic regions can be used to assess what peatlands are especially vulnerable to climate change mediated drought.

Monitoring of Soil Water Content in Maize Rotated with Pigeonpea Fallows in South Africa

Maize production under smallholder systems in South Africa (RSA) depends on rainfall. Incidences of dry spells throughout the growing season have affected maize yields negatively. The study examined water distribution and water use efficiency (WUE) of maize rotated with two-year pigeonpea fallows as compared to continuous maize without fertilizer. A randomized complete block design, replicated three times, was used with four treatments, which included continuous unfertilized maize, natural fallow-maize, pigeonpea + grass-pigeonpea-maize, and two-year pigeonpea fallow-maize. Soil water mark sensors were installed 0.2; 0.5; and 1.2 m on each plot to monitor soil water tension (kPa). Soil samples were analyzed using pressure plates to determine water retention curves which were used to convert soil water tension to volumetric water content. Maize rotated with two-year pigeonpea fallows had higher dry matter yield (11,661 kg ha−1) and WUE (20.78 kg mm−1) than continuous maize (5314 kg ha−1 and 9.48 kg mm−1). In this era of water scarcity and drought incidences caused by climate change, maize rotated with pigeonpea fallows is recommended among smallholder farmers in RSA because of its higher WUE, hence food security will be guaranteed.

Tensiometers for Rice Water Footprints

Water footprints (WFs) of rice are quite higher viz. 992 billion cubic metres per year (Gm3 yr−1) than from the other cereals which further responsible for the lower water productivity. Out of global WFs for crop production viz. 7404 Gm3 yr−1 corresponds to 78 % green, 12 % blue, and 10 % grey water, respectively. Around 3000-4000 litres of water required for one kg of rice grains and conventional puddle transplanted flood irrigations responsible for this. Therefore, there is an urgent need to cut down rice WFs share. Over irrigated pounded water under conventional puddle transplanted rice responsible for the emissions of the green house gases in atmosphere, which further has its own complications. With time, due to excessive withdrawals of the underground water, the water table is declining at a faster rate and seems to be beyond the reach of the middle class rice farmers. Rice water productivity declining day by day due to huge water demand of rice crop followed by reduced yields. A major share of the applied irrigation water lost/evaporate in the atmosphere. Soil water tension controls the soil moisture dynamics and directly linked to the plant need based approach. Being a kharif crop, rice season faces harsh summers and where evaporative demands of atmosphere intensified to many folds and thus, irrigation water has to be applied frequently. Annually additional water of worth US $ 39 million is withdrawn in NW Indian Punjab state for feeding crops, particularly rice. Tensiometer is the only instrument provided to the rice farmers for applying irrigation water judiciously based on the plant need which further cut down WFs from 18 to 22%. This practise where on one side saves irrigation water, improves declining land as well as water productivity of rice, also controlled the emissions of GHGs from the soil.

Content of basil essential oil on a loam texture soil under water regimes and different harvest stages

The essential oil of basil (Ocimum basilicum L.) has high economic value and is produced in the plant by secondary metabolism. Its quantity and composition tend to vary as a response of the plant to stress situations due to changes in the environment and phenological phase. This work aimed to evaluate the development, the chemical composition, content, and the yield of essential oil of basil rich in Linalool, as a function of the soil water tensions and the harvest stages, in a loam texture soil. The experiment was carried out in a greenhouse and consisted of three harvest times (BF - beginning of flowering, FF - full flowering, and EF - end of flowering) and five values of soil water tension to define when to irrigate (20, 30, 40, 50, and 60 kPa), totalizing 15 treatments. The irrigation in the soil water tension of 60 kPa generated a reduction in the content and the yield of essential oils compared with 20 kPa, only in the FF harvest stage. However, it did not modify the composition of the essential oil. Regardless of the soil water tension to define irrigation, the highest levels and yields of essential oil were found in the EF harvest stage. Harvest stages did not change the composition of the essential oil or the content of Linalool. In turn, the contents of the components Cineol, Camphor, ∝-Terpeneol, and Isobornyl acetate increased with the harvesting period from BF to EF. Eugenol had the opposite trend, reducing the content from BF to EF. Linalool, a component in greater proportion in essential oil, showed a higher content in soil water tensions up to 50 kPa, decreasing only by 60 kPa. In loam textured soils, it is recommended that basil producers, who aim to extract Linalool, irrigate when the soil water tension reaches up to 50 kPa, with the harvest at any stage of flowering.

Bell Pepper Development and Water Potential as Affected by Soil Water Tensions and Nitrogen Doses

Considering the lack of technical information on the water depth and nitrogen fertilization via fertigation in bell pepper cultivation, this work aimed to provide management data for its production in the northern region of Brazil. The experiment was carried out in a greenhouse at FEIGA / UFRA, with a 1.0 x 0.50 m spacing, in a randomized block design, with a 5 x 4 factorial scheme, with three replications. The treatments consisted of five water tensions in the soil (15, 25, 35, 45 and 65 kPa) and four nitrogen doses (0, 135, 265 and 395 kg.ha-1). There was no interaction between the factors of water tension in the soil and nitrogen doses for any of the variables analyzed. Height of plants, fresh shoot mass and dry shoot mass showed significant differences only for nitrogen doses. Predawn potential, showed significant difference for soil water tensions and nitrogen doses. Ahead of the conditions under which this work was carried out and the results obtained for the variables analyzed for the bell pepper cultivation in a protected environment, we found that the soil water tension of 15 kPa and the nitrogen dose of 265 kg.ha-1 were ideal for the crop.

YIELD OF FERTIGATED BELL PEPPER UNDER DIFFERENT SOIL WATER TENSIONS AND NITROGEN FERTILIZATION1

ABSTRACT Considering the lack of technical information on the water depth and nitrogen fertilization via fertigation in protected cultivation for bell pepper production in northern Brazil, this paper aimed to study the soil water tensions under different nitrogen doses for the cultivation of bell pepper in protected environment. The experiment was conducted in a greenhouse at the Igarapé-Açu School Farm of the Federal Rural University of the Amazon, at 1.0 x 0.50 m spacing, using the experimental design of randomized blocks in a 5x4 factorial scheme, with three replicates. The treatments consisted of five soil water tensions (15, 25, 35, 45 and 65 kPa) and four nitrogen doses (0, 135, 265 and 395 kg ha-1). There was interaction between soil water tension and nitrogen doses only for nitrogen use efficiency, and the best value was obtained with the combination between soil water tension of 15 kPa and nitrogen dose of 135 kg ha-1. Total number of fruits, fruit length and fruit diameter showed significant differences only as a function of soil water tensions. Production per plant, total yield and water use efficiency were statistically significant for soil water tensions and nitrogen doses. Therefore, for the conditions in which this study was carried out, it is recommended to apply a soil water tension of 15 kPa and nitrogen dose of 265 kg ha-1 for bell pepper cultivation in protected environment.