Sustainable Technology to Reduce Energy Use in Travelling Sprinkler Irrigation

Hose reel irrigation entails high energy consumption especially when water is supplied by big gun sprinklers. Despite much of the energy being used to put water under pressure, additional amount of energy is required for positioning (towing by tractor) and rolling (towing by reel machine) the travelling cart. Moreover, under field conditions such as missing cart lane (e.g., pipe to be unrolled over actual crop when complementary irrigation is practiced) or light rainfall just moisturizing the surface of clay soils (e.g., mud hindering the sliding movement of the pipe), positioning of a travelling cart supporting either big gun or boom sprinkler can be difficult. Critical conditions may occur also when long pipes are used and the tractive force of the tractor is inadequate (i.e., unable to completely unroll the pipe). On the other hand, larger tractors can overcome the problem, at the price of strong mechanical stress on the pipe (e.g., elongation), increased fuel consumption and higher investment and overheads. During pipe retrieval, power supply is in charge of the machine. In spite of the low rewinding speed (e.g., 20 to 30 meters per hour), similar stress to the pipe can occur. In addition, mechanical components of the machine (i.e., reel and gear) are subjected to abnormal stress and, in some cases, rollover prone conditions can arise due to unexpected lateral movements of the machine. Energy used for these operations is expected to vary with the length of unrolled pipe, pipe weight (e.g., whether empty or filled) and friction coefficient between pipe and surface during relative movement. In order to reduce the aforementioned problems and limitations, an innovative system named Protector was conceived by Irriland srl, an Italian manufacturer of reel machines, and developed with the support of the GESAAF Department of the University of Florence. During cart pulling for positioning at the field far end, the pipe unrolls from the reel machine, while the tape does the same from the cart reel and lays down on the ground, under the hose. During irrigation, both pipe and tape roll up in the respective reel. The result is that friction between soil and sliding pipe is replaced by friction between tape and sliding pipe, which is lower due to the characteristics of the tape. The length of the tape is at least equal to that of the irrigation pipe. Field tests, still in progress, aim to investigate and assess the potential advantages allowed by Protector, which in principle consists of a tape, about 60 cm wide, made of recycled plastic, rolled up in a small reel positioned in the travelling cart. Two prototypes, coupled to machines having different pipe lengths and diameters, have been used on Sugarbeet and Alfalfa in order to assess the influence of the tape on the traction force necessary for the movement of the travelling cart in different conditions (i.e., with and without Protector, whether pipe is filled or empty). According to results, traction force increases linearly and Protector tape is able to reduce dramatically (i.e., from about 30% onwards) the sliding friction occurring during pipe unrolling, regardless of crop type, pipe diameter and length. When filled of water, about 30% additional traction force has to be applied. Under test conditions, applied traction force to protected empty pipe does not exceed 1 ton/250 m of unrolled pipe in all cases. This condition can allow the use of lighter pipes (i.e., thinner thickness given the same outer diameter), so potential advantages, such as reduced energy use for water lifting and emission of Greenhouse Gases (GHG), reduced energy consumption and impact during PE pipe production, reduced monetary cost for the farmer due to non replacement of the standard pipe (e.g., working in protected sliding conditions), were assessed under irrigation scenario that is normal in sub humid Mediterranean climate (i.e., 210 mm seasonal irrigation depth). Results indicate that GHG emissions due to water lifting is reduced up to 25.5 %, while emissions during PE pipe production, assessed according to the Life Cycle Analisis (LCA), are reduced from 37% to 69% depending on whether pipe lifetime is equal to or shorter than that of the machine, respectively. Under the reasonable hypothesis of replacing the standard pipe (i.e., Protector is not used), total cost for the farmer and impact on climate increase by 48.7% and 39.6%, respectively, at the end of the economic lifetime of the machine. It should be noted that energy use for pumping is by far both the main source of GHG and cost for the farmer, and that the use of lighter pipes, allowed by Protector, can reduce dramatically both GHG emissions and pumping cost.