1. Field of Art
The present invention generally relates to soil measurement and testing, and more specifically, filtration of a soil-extractant mixture.
2. Description of the Related Art
Nutrient levels in soil have significant spatial and temporal variations. Accordingly, there has been significant effort placed into development of local nutrient management schemes, often referred to as “precision agriculture,” addressing nutrient level variation. Local nutrient management increases agricultural efficiency while reducing its environmental impact by allowing growers to locally apply nutrients where needed. Increases in nutrient costs and a growing awareness of the environmental consequences of current agriculture practices have made improvements in agricultural efficiency and environmental impact increasingly important.
For example, fertilizer inputs are a large fraction of agricultural input costs and prices of nutrient input have almost doubled in recent years, increasing concern about future price fluctuations among growers. Meanwhile, in addition to long-standing concerns about the effect of fertilizers on water quality, greenhouse gas emissions caused by nitrogen-based fertilizers have become an increasing concern. For example, it is estimated that N2O emissions caused by fertilizer volatilization are responsible for 5-10% of the forcing for global warming. Thus the ability to optimize the use of fertilizer inputs, and nitrogen-based fertilizers in particular, is increasingly recognized as a vital component of environmental sustainability. As a result of these factors, there is a rapidly growing interest in more efficient nutrient management.
Local measurement of soil nutrient levels is a significant component of local nutrient management scheme. However, conventional methods for locally measuring soil nutrient levels have limited the effectiveness of existing local nutrient management schemes. Conventionally, capturing a number of samples/acre at the appropriate time to make effective decisions is often prohibitively time consuming and expensive. For example, lettuce growers in certain area typically plant several crop cycles each year, and have a five day window between harvesting and planting the next crop. Logistically, this results in a very small time window, 1-2 days, in which to sample the field and apply fertilizer. This short time frame prevents use of standard laboratory-based soil testing, which often takes 1-2 weeks to provide a result. Consequently, growers typically make decisions on fertilizer application based on historical analysis, instead of on current soil conditions.
As another example, in-season nitrogen management in corn-growing regions is often difficult because of the slow turnaround time of laboratory-based soil testing. Extending the time when corn growers are able to measure soil nitrogen levels would allow corn growers to test fields before their last application of fertilizer. This enables corn growers to test fields later in the growing season and implement nitrogen management practices. Further, allowing growers to promptly retest fields, such as retesting after a rain, allows growers to adopt more efficient nitrogen management practices. Additionally, laboratory-based soil measurement costs scale directly with the number of samples, making it prohibitively expensive to sample at high grid densities. Thus, the development of a fast, simple, and inexpensive soil would expand the benefits of precision agriculture.
Additionally, standard laboratory-based tests are relatively slow and expensive. For example, a traditional laboratory-based test may use a filtration system that incorporates a filter that operates using the force of gravity. For example, gravity acts on a liquid mixture to generate filtrate for a measurement. This process is not only tedious but requires frequent replacement of filters, ideally a new filter for each sample processed. Labs may speed up these measurements by creating a vacuum on the filtrate side of the filter to generate a negative pressure differential to increase the rate of filtrate generation. Such methods are often used in controlled lab environments with specialized and fragile lab equipment such as Buchner flasks with a vacuum pump and the like. Such setups are impractical for use in the field.
Accordingly, there have thus been numerous efforts to develop various other fast soil nutrient detection tools for use in the field. Technologies used include mid-infrared (mid-IR) spectroscopy, ion-selective electrodes, and chemical-reaction based strip tests. However, the use of each method has suffered from some combination of expense, low accuracy, stringent calibration requirements or difficulty of use.
Accordingly, a rapid and economical system for soil analysis that does not require a controlled lab environment could provide more accurate and timely nutrient management recommendations which improve agricultural efficiency.