Increasing image resolution and shrinking camera size facilitates easy mounting of digital cameras on Unmanned Aerial Vehicles (UAVs) to collect large amounts of high-resolution aerial photos for soil surface and vegetation monitoring. Major challenges remain geo-referencing of these images, reliable stitching (mosaicking), elimination of geometric image distortions and compensation of limited image quality and high cost of the equipment. In this study, we report upon the design and field-testing of a custom-made, cost-effective mini-UAV allowing the acquisition of RGB and near-IR images covering areas of 1–2 km2 in each flight and the development of a software tool to automatically combine the geo-referenced images into a seamless image mosaic. Object-orientated image classification was used to estimate plant biomass. The images allowed to determine the distribution and biomass of selected plant species and other landscape features such as field borders and settlement patterns as well as to construct a simple 3D model of the topography of the surveyed area. The setup facilitates the cost-effective acquisition, mosaicking and classification of hundreds of RGB and near-IR images with a spatial resolution of 5–10 cm.

Plant breeding makes genetic gains over years, so growing newer varieties generally provides greater benefits than growing older ones. However, in low-altitude districts of Nepal, a few rice varieties covered 75% of the rice area and were more than 20 years old (first paper in this series). We test here if this slow rate of adoption of new varieties could be accelerated using a participatory method, Informal Research and Development (IRD), where packets of seeds of new rice varieties are widely distributed to many farmers. From 2008 to 2011, over 117 000 IRD packets were distributed in 18 districts of the Nepal Terai, including over 70 000 of three released varieties from a client-oriented breeding (COB) programme in Nepal. The IRD significantly increased the adoption of the three COB varieties. The benefits obtained by farmers in a single growing season equal the costs of IRD, if for every 75 kits distributed an additional 1 ha is grown. This assumes that the new varieties produce a 10% increase in yield (lower than that evidenced in their release proposals). On an average, fewer than three IRD kits were distributed for each hectare of a new variety grown by farmers in 2011. Furthermore, the effectiveness of IRD could be increased 1.2 to 2.7 fold (depending on the COB variety) if the IRD distribution were to be restricted to the region where the variety was most accepted. The best comparison of IRD with extension by the conventional system was their popularity compared with similar-aged varieties that had been promoted in the two systems. The adoption of three COB varieties was about twicethat of three varieties from the National Rice Research Programme (NRRP) that were closest in release date to the COB varieties. Unlike cost effectiveness assessed by hectares grown per IRD kit distributed, this comparison can only indicate efficacy because, as well as extension method, many factors influenced the adoption rates of the COB and NRRP varieties. The costs of IRD are small, both relative to the cost of breeding new varieties and to the benefits gained; so it is one of the simplest and most cost-effective interventions to increase agricultural productivity.

The capability of some plant species to mobilize phosphorus (P) from poorly available soil P fractions can improve P availability for P-inefficient plant species in intercropping. White lupin (Lupinus albus) has been investigated as a model P-mobilizing plant for its capability of enhancing the P acquisition of neighbouring species under P-limited conditions. To date, investigations have led to contrasting findings, where some reports have described a positive effect of intercropped lupins on companion plants, whereas others have revealed no effects. This review summarizes the literature related to lupin–cereal intercropping. It explores the underpinning mechanisms that influence interspecific facilitation of P acquisition. The P-mobilization-based facilitation by lupins to enhance P-acquisition of co-occurring plant species is determined by both available P concentration and P-sorption capacity of soil, and the root intermingling capacity among two plant partners enabling rhizosphere overlapping. In lupin–cereal intercropping, lupin enhances the below-ground concentration of labile P pools through mobilization of P from sparingly available P pools, which is accomplished through carboxylate exudation, where neighbouring species acquire part of the mobilized P. The non-P-mobilizing species benefit only under P-limited conditions when they immediately occupy the maximum soil volume influenced by P-mobilizing lupin. Positive effects of mixed cropping are apparent in alkaline, neutral and acidic soils. However, the facilitation of P acquisition by lupins to companion species is eliminated when soil becomes strongly P-sorbing. In such soils, the limitation of root growth can result in poorer root intermingling between two species. The P mobilized by lupins might not be acquired by neighbouring species because it is bound to P-sorbing compounds. We suggest that the lupins can be best used as P-mobilizing plant species to enhance P acquisition of P-inefficient species under P-limited conditions when plant species are grown with compatible crops and soil types that facilitate sharing of rhizosphere functions among intercropped partners.