Development of Suitable Microclimate Using Low˗tech Greenhouse for Off-Season Production of High Value Crops in Bangladesh

Low˗tech greenhouses (low˗techs) have been used globally to cultivate horticultural crops since many years, but their utilization in Bangladesh is a recent phenomenon. Moreover, information on altered microclimate inside the low˗tech is hardly reported. An investigation has been conducted in the Crop Botany Field Laboratory, Bangladesh Agricultural University (24o72´N, 90o43´E and 18 masl), Mymensingh during the late autumn to winter seasons from mid-October to mid-February of 2015/16, 2016/17 and 2017/18 years to find out the variation in microclimatic parameters between inside and outside of low˗techs and to evaluate the suitability of altered microclimate inside the low˗techs for off˗season production of high value crops in Bangladesh. Three low˗techs were erected in each year using bamboo frame covered with single inflated polyethylene film (thickness = 0.2 mm). Major microclimatic parameters inside and aside outside the low˗techs were measured with standard devices or techniques. Around 30 percent incoming photosynthetically active radiation (PAR) was cut˗off by low˗tech cover during solar noon when the sun’s zenith gets minimum value (around 0o). However, this cut˗off portion of PAR was gradually increased with the sunrise and sunset when zenith is around 90o. During the daytime, low˗tech retains higher air temperature than that found at outside and the differences in air temperature between inside and outside of low˗techs was gradually increased after sunrise with a peak difference of 7 to 9 oC following the solar noon (i.e., 13:00-14:00 hour). No distinct variation in relative humidity was recorded between inside and outside of the low˗tech. Low˗tech cover retains higher soil temperature than that was recorded in outside. The variation of both air and soil temperatures between inside and outside of low˗techs was higher during the daytime but lower at nighttime or even at daytime when the sky remained overcast. The variation in microclimatic parameters under low˗techs not only protect the growing crops from climate vagaries during autumn, winter and spring seasons but also provide suitable warmer environment for growing many high value crops during that seasons and thus crop production in off˗season and/or season extension benefits can easily be achieved by low˗techs.

Effect of shelterbelt on the microclimate of the gram (Cicer arietinum) crop

The shelterbelt influence on the microclimate of gram crop in different intercropping systems comprising of four treatment, viz., pure gram, 1 : 1, 2 : 1 and 4 : 1 gram and raya, was quantified. Albedo varied from 14.8 to 22.6 percent in various treatments with highest value fo 18.3 percent in pure gram treatment, whereas, photosynthetically active radiation absorption was highest in 2 : 1 gram treatment (76%). Maximum reduction (69.2 per cent) in wind speed was observed in 1 : 1 intercropping system at 4h distance from the edge of the shelterbelt in comparison to pure gram field. Relative humidity was 8 to 15 percent less in the sheltered gram as compare to the pure gram, whereas, the average air temperature increased by 1 to 2 C in the sheltered crop over that of the pure gram and this increase was in the range of 9.9 to 12.2 per cent at 4h distance from the edge of shelterbelt. The grass minimum temperature was higher by 0.7degree cent grate in 2 : 1 treatment over that of pure gram during the months of January and February.

Do Greenhouse Cover Materials Affect Cannabis Performance?

A greenhouse pot experiment was conducted in the Agricultural University of Athens in order to evaluate the effect of several greenhouse cover materials on the performance and yield of hemp. The experiment was set up in a completely randomized design (CRD) with five treatments/greenhouses (G1, G2, G3, G4/Control, and G5). Measurements included plant height, PAR (Photosynthetic Active Radiation), chlorophyll content, solar irradiance, soil and leaf temperature, and yield components (the number of buds, their weight, length, and compact index, CBD content, and CBD yield per plant). The results of the present study suggest that the different polyethylene cover films alter the environment within the greenhouse and thus, affect the agronomic characteristics and yield traits of hemp. G1 reported the best results as it increased soil temperature and PAR values by 11-16% and 50-110% respectively, compared to G4. Concurrently, the majority of the bud characteristics were significantly improved in G1. Even though further research should be conducted in order to define the most suitable films for greenhouse hemp production, our results indicate that the optical properties of the greenhouse cover materials affect its yield and should always be considered.

Correcting PAR data from photovoltaic quantum sensors on remote weather stations on the Great Barrier Reef

The study addresses a network of remote weather stations on the Great Barrier Reef that house Licor192 quantum sensors measuring photosynthetically active radiation (PAR) above water. There is evidence of significant degradation in the signal from the sensors after a two-year deployment. Main sources of uncertainty in the calibration are outlined which include degradation of the photodiode, soiling of the sensors by dust and salt spray, cosine responses and sensitivity to air temperature. Raw PAR data are improved using correction factors based on a cloudless PAR model. Uncertainties in cosine responses of the instrument are low but significant errors may occur if the supporting platform is mis-aligned and not horizontal. A set of recommendations are provided to improve the quality of the PAR data.

Solar Radiation Transmittance Characteristics of Textile Woven Fabrics suitable for Greenhouse covering Materials

Nowadays, greenhouse covering materials have a vital role in terms of a protective cultivation process. Many farmers use polyfilms, rigid or semi-rigid plastic panels, and glazing materials as greenhouse covering materials in the present scenario. However, these plastic covering materials are known for their high cost, short service life, and cause of harmful environment. Solar transmittance property is one of the main criteria for choosing any greenhouse covering materials. This study prepares various woven fabrics made of polyester, cotton, and polyester–cotton blend yarns. Their solar transmittance characteristic is analyzed to develop fabric and compare it with a polyethylene film already used as a greenhouse cladding material to substitute for plastic materials. The solar transmission of polyester fabric is achieved as high as 70% in the photosynthesis active radiation, suitable for a commercial greenhouse material. In addition, the polyester fabric has tensile strength and extension much higher than that of commercial plastic greenhouse material.