Organic waste recycling in agriculture and related effects on soil water retention and plant available water: a review

The decrease of organic matter content in agricultural soils is a problem of great concern to farmers around the world. Indeed, it lowers soil fertility that directly impairs agricultural crop production and affects a number of other soil properties like water retention capacity, aggregation and structure formation, soil mechanical strength or compactibility. Scarcity in plant available water poses a risk to agriculture, especially in drought-prone areas. However, the increase of organic waste recycling in agriculture may also lead to an increase in soil organic matter contents and to changes in related soil properties. Here, we review 17 long-term field experiments (>= 9 years) that investigated the effects of organic amendments on organic carbon and water availability in topsoils. We paid particular attention to the effects of added organic matter on soil bulk density or porosity and consequently on plant available water. Our main findings are that (1) plant available water generally improves after organic waste addition (relative changes from -10 to +30 vol%; p = 0.052), (2) organic matter quality affects changes in organic carbon (p < 0.05), (3) it is more suitable for plant available water quantification to use volumetric rather than gravimetric water contents, (4) the value of the matric potential defining field capacity is an issue, (5) pedotransfer functions developed for American soils adequately predicted most water contents at field capacity and wilting point, and (6) prevailing climate and initial organic carbon content may affect plant available water. This review confirms that organic amendments generally induce beneficial effects on plant available water and other soil properties. It also highlights the influence of organic matter quality on soil organic carbon. Compared with a previous review, this study reinforces reported trends of increasing plant available water with organic waste additions. This may be due to a more restrictive selection of recently published data and the use of volumetric water contents. Our findings are significant for sustainable agriculture regarding the sustainable use of organic wastes and water.