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Design and evaluation of modified screen net house for off-season vegetable raising in composite climate

机译：复合气候下淡季蔬菜栽培改良型筛网房屋的设计与评价

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摘要

Currently the use of conventional screen net houses for off-season vegetable raising in north India composite climate is not so effective and has many constructional and operational limitations like poor structural design, higher constructional cost, no greenhouse effect in winter and higher plant temperatures in summer. Similarly, the use of polyethylene sheet covered greenhouses also has problems like much higher constructional and operational costs and higher inside air temperatures in summers. In this study, modified designs of 500 m~2 (one kanal) and 250 m~2 (half kanal) screen net house have been presented particularly suitable for composite climate (where both winters as well as summers are harsh) as a replacement for conventional net house and polyethylene sheet covered greenhouse design. To make these designs low cost and more effective, low tunnels (covered with low density polyethylene sheet) have been designed and used in winter over the plant rows to generate localized greenhouse effect for faster plant growth. By doing so, average daily air temperature under the tunnels was raised about 9-10℃ above the open field air temperature. In this way, huge cost of covering the net house or greenhouse during winter with costly polyethylene sheet could be saved. Similarly, in extreme summer when the ambient air temperature exceeded 40℃ (during the fruiting stage of the crop) a 50% shade net was used inside the modified net house at 2.5 m height (instead of using active cooling system) resulting in 4-6℃ drop in the plant temperature. Experimental evaluation of the modified net house was conducted during winter and summer months of year 2007-08 (December to June) by growing brinjal crop and compared with conventional net house, polyethylene sheet greenhouse and in open field condition. It was observed that due to the combined effect of low tunnels (in winter) and shade net (in summer), the micro-climatic parameters like air temperature, plant temperature, solar radiation and light intensity remained within desirable range during different stages of crop growth resulting in 37.6% and 11.5% increase in the yield of brinjal crop as compared to conventional net house and PE covered greenhouse yield, respectively, at 31°N latitude. Economic analysis of the modified net house was also conducted and compared with the conventional net house and PE covered greenhouse of the same area. It was observed that 500 m~2 area modified net house (coupled with low tunnels and shade net) produces highest yield and has the highest net present worth (Rs 3,35,324) and the lowest payback period (5.2 years) as compared to the conventional net house (Rs 2,04,712 and 6.5 years) and PE covered greenhouse (Rs 1,52,614 and 10.5 years). On the other hand for 250 m~2 modified net house, the net present worth and payback period was Rs 1,20,417 and 9.7 years as compared to Rs 65,497 and 11.5 years and Rs 10,616 and 17 years for conventional net house and PE covered greenhouse.
机译：当前，在印度北部的复合气候中，使用常规的筛网房屋进行淡季蔬菜种植并不那么有效，并且存在许多施工和操作上的局限性，例如不良的结构设计，较高的建造成本，冬季无温室效应和夏季较高的植物温度。同样，使用聚乙烯覆盖的大棚也存在一些问题，例如更高的建筑和运营成本以及夏天的室内空气温度更高。在这项研究中，提出了500 m〜2（一个卡纳尔）和250 m〜2（半卡纳尔）筛网房的改进设计，特别适合于复合气候（冬季和夏季都比较恶劣）的替代方案。传统的网箱和聚乙烯板覆盖温室设计。为了使这些设计成本更低，更有效，已经设计了低通道（覆盖有低密度聚乙烯板），并在冬季在植物行上方使用，以产生局部温室效应，从而加快植物生长。这样，隧道下的日平均气温比野外气温高出约9-10℃。这样，可以节省在冬天用昂贵的聚乙烯片材覆盖网状房屋或温室的巨大成本。同样，在极端的夏季，当环境空气温度超过40摄氏度时（在农作物的结实阶段），在改良后的网箱内部以2.5 m的高度使用了50％的遮阳网（而不是使用主动冷却系统），导致4工厂温度下降6℃。在2007-08年冬季和夏季（12月至6月）通过种植茄子作物进行了改性网棚的实验评估，并将其与常规网棚，聚乙烯薄板温室和露天环境进行了比较。观察到，由于低隧道（冬季）和遮阳网（夏季）的共同作用，在作物的不同阶段，气温，植物温度，太阳辐射和光强度等微气候参数保持在理想范围内在北纬31°时，与常规的网房和PE覆盖的温室相比，茄子的产量分别增长了37.6％和11.5％。还对改造后的网箱进行了经济分析，并将其与常规网箱和相同区域的PE覆盖温室进行了比较。观察到，与之相比，面积为500 m〜2的改建净房屋（加上低隧道和遮阳网）产生的产量最高，净现值最高（3,35,324卢比），投资回收期最低（5.2年）。传统的净温室（2,04,712卢比和6.5年）和PE覆盖的温室（1,52,614卢比和10.5年）。另一方面，对于250 m〜2的改良净房屋，净现值和投资回收期为1,20,417卢比和9.7年，而常规净房屋和PE覆盖温室的净现值和投资回收期为65,497卢比和11.5年，以及10,616卢比和17年。 。

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