Storing vs economizing water in agricultural landscapes ?

Picture copyright Cattiau, Inra

Scientists Allain et al., using a modeling platform, revealed that reducing water use does not necessarily improve downstream river flows nor decrease crop yields. Symmetrically, they showed that a new distribution of reservoirs can highly impact the water consumption and the agricultural economy without changing the water storage capacity. These are new reasons to argue that solving water imbalances is not only a matter of storing versus economizing water!

Organic wastes improve plant water supply

Picture copyright Houot

Plant available water is held in soil pores, which size is affected by soil organic matter content. Organic waste recycling in agriculture can increase soil organic matter contents and improve related soil properties. Agronomists Eden et al. analyzed data from long-term field experiments and found that in almost all cases, plant available water is increased in soils amended with organic wastes.

Human virus contamination from sprayed wastewater

Picture copyright GIRARDIN et al.

Domestic wastewaters are used to irrigate soils, thus saving pristine waters. However wastewater contains human enteric viruses that may contaminate the atmosphere after wastewater spraying. Scientists Girardin et al. found that 11-89% of murine mengoviruses applied to the soil were aerosolized during the first half hour. They have developed a model to help policymakers refine standards governing wastewater reuse in irrigation.

Farming without irrigation

Picture copyright ANDERSON et al.

Rainfed agriculture refers to farming that relies solely on rainfall for crop growth, versus irrigated agriculture that use extra water. Rainfed agriculture accounts for 60-95% of farmlands in developed countries in Africa, Asia and Latin America. Agronomists Anderson et al. review recent research on rainfed agriculture and suggest that conservation agriculture should improve soil water content and, in turn, crop yields.

Deficit irrigation to save water in agriculture

Picture copyright PITSCH, INRA
Picture copyright PITSCH, INRA

Agriculture consumes more than two-thirds of the planet freshwater. As a consequence there are conflicts of freshwater allocation between agriculture and other water users. There is therefore a need for advanced methods to save water in agriculture. Scientists Gan et al. found that regulated deficit irrigation is an alternative method that saves large amounts of water without yield decrease. Moreover, deficit irrigation enhances plant adaptation to drought stress.

 

Strategies for agriculture with less water: back to the roots

Climate change is decreasing water content in many parts of the world. There is therefore a need to adapt by designed practices that save water and use less water. This can be done for instance by reduced tillage, mulching, selecting drought-tolerant cultivars and synchronizing plant demand with rainfall. Bodner et al. describe the most efficient strategies for better water management under dry climate. They found that selecting plant roots is a promising solution, yet still overlooked.

 

Water saved by wheat-maize relay planting with straw covering

Relay planting is planting seeds of a new crop among the plants of a mature crop so they will have a head start when the mature crop is done. As a consequence more crops per year can be brought to maturity in the same planting space. In northwestern China maize is planted about 40 days after wheat seeding, and this relay planting is popular for high yields. Yin et al. show that relay planting with reduced tillage and stubble mulching increases water use efficiency up to 46%.

 

Rice cultivation with less water

Rice is traditionally cultivated by transplantation by farmers in water. However there is an increasing scarcity of water in a time of climate change. Moreover, transplanting in water is costly because many workers are needed. Therefore dry direct-seeded rice cultivation appears as a promising alternative. Liu et al. have compared dry direct-seeded rice and transplanted-flooded rice. They propose that dry direct-seeded rice should successfully replace transplanted rice in Central China due to less water requirement, identical grain yield and higher resource use efficiency.

 

Irrigation increases soil carbon and greenhouse gas N2O emissions

Irrigation controls food production as plant do not grow without water. The article by Trost et al. review the effects of irrigation on soil carbon and greenhouse gas N2O emissions. Findings include that irrigation increases soil carbon up to 500 % in  cultivated deserts and up to 35% in semiarid regions. In humid regions N2O emissions often increase after precipitation or irrigation.