Higher-than-recommended fertilizer application is considered by farmers as insurance to maintain sufficient levels of plant nutrients during periods of excessive rainfall, or to capitalize on favorable market conditions and facilitate an extended harvest period. In addition to increasing the likelihood of eutrophic waters, excess fertilizer application may exacerbate soil salinity that reduces yields and economic benefits after extreme weather events such as hurricanes. Research-based fertilizer recommendations are needed to address global eutrophication of fresh water systems. A three-year, four-season study evaluated the effects of higher-than-recommended nutrient and water inputs on tomato (Solanum lycopersicum) yield and farm profitability under normal and extreme weather conditions in subtropical Florida, a major fresh vegetable producing region. Three nutrient-water management treatments were considered: conventional high fertilizer rate with subirrigation (High-Sub), recommended (best management practice) fertilizer rate with subirrigation (Rec-Sub), and recommended fertilizer rate with subsurface drip irrigation (Rec-Drip). There were significant differences in yield between seasons (i.e., Fall, Year 1 = 52,742 kg ha⁻¹; Fall, Year 2 = 22,045 kg ha⁻¹; Spring, Year 3 = 78,926 kg ha⁻¹; and Fall, Year 3 = 61,905 kg ha⁻¹). Yield reductions in Year 2, an unusually wet season affected by Hurricane Wilma (21 cm rain in 11 hours), were related to high nitrogen (N) losses and soil salinity (electrical conductivity > 2,500 μS cm⁻¹). Average groundwater N, seasonal groundwater electrical conductivity, and soil N indicated high salt concentrations and leaching in High-Sub especially during Fall Year 2. There were no statistically significant yield differences among treatments. Growers, however, tend to look at the differences in average yields for trends in farm profits and losses. With this perspective in mind, we conducted a grower-type economic calculation using prevailing market prices that showed additional revenues (US$12,000 ha⁻¹) from Rec-Sub and Rec-Drip during Fall Year 2, which almost entirely balanced the lower revenues for remaining seasons. National market prices for tomato were highest during Fall Year 2 due to extensive crop damage (wind and flooding) from Hurricane Wilma. Given the average frequency of a tropical storm/hurricane being three years, growers may enjoy an economic benefit once every three years from not applying excess fertilizer, and at the same time, avoid external environmental costs that include publicly funded treatment systems. Reduced groundwater nutrient concentration (N = 61% and phosphorus [P] = 42%) in Rec-Sub could achieve similar reductions in nutrient loads in regions such as Florida, which have significant surface water and groundwater interaction. Future increases in frequency and magnitude of extreme events (e.g., 2017 Hurricane Irma, rainfall = 37 cm) may exacerbate the impacts on production and water quality. Therefore, excessive fertilization is not likely to be economically or environmentally sustainable.

Study region\ud \ud Three districts in crystalline aquifer region of semi-arid south India.\ud \ud Study focus\ud \ud India, world’s largest groundwater user (250 billion m3 yr−1) has been reported to experience declining groundwater levels. However, the statistical significance of the decline has not been analyzed to separate human effects from natural variability. Trends in groundwater levels in three administrative districts of south India were analyzed and explained through changes in irrigation, rainfall, and agricultural power subsidy.\ud \ud New hydrological insights for the region\ud \ud Contrary to common perception of widespread groundwater declines only 22–36% of the wells showed statistically significant declines. The use of well depth during dry well periods may slightly underestimate the number of declining wells (by 1%) and rate of decline. Increase in groundwater irrigated area combined with rainfall and power subsidy policy, were the main causative factors for the decline. Groundwater decline after implementation of free-electricity policy in 2004 confirmed the nexus between power subsidy and groundwater. These declines are likely to worsen due to future well drillings. Trends in other regions with similar hydro-geologic conditions need to be analyzed to verify groundwater declines and its linkages with power subsidy. Once established, reforms in power subsidy and well permit policy along with conversion to efficient micro–irrigation may be needed to maintain or enhance groundwater availability in the crystalline aquifer region of India (240 million ha)

Rice production is important for global food security but given its large water footprint, efficient irrigation management strategies need to be developed. Expansion of rice growing area is larger than any other crop in Africa due to increasing demand for rice. Three rice irrigation management alternatives with the system of rice intensification (SRI) were field-evaluated against the conventional continuously flooded system (CF) in Tanzania. Production systems included: (1) CF (50 mm ponding depth for the entire season); (2) SRI (40 mm ponding for 3 days and no irrigation for next 5 days); (3) 80% SRI (80% of the SRI ponding); and (4) 50% SRI (50% of the SRI ponding). Experimental evaluation of the four systems was conducted for both wet and dry seasons. For the dry season, the SRI and 80% SRI produced higher yields of 9.68 tons/ha and 11.45 tons/ha and saved 26% and 35% of water, respectively compared to the CF (8.69 tons/ha). The yield advantage of the 80% SRI and SRI over the CF was less during the wet season with 6.01 tons/ha and 5.99 tons/ha of production, and water savings of 30% and 14%, respectively compared to the CF (5.64 tons/ha). The 50% SRI had lowest yield of all for both seasons, 7.48 tons/ha and 4.99 tons/ha for the dry and wet seasons, respectively. Statistically, the 80% SRI treatment outperformed all other treatments over the two seasons with an additional yield of 1.57 tons/ha and 33% (345 mm) water savings compared to the CF. Economic productivity of water (US$/ha-cm) over two seasons was highest for the 80% SRI ($20.27/ha-cm), while it was lowest for the CF ($12.89/ha-cm). Water saved by converting from the CF to the 80% SRI (1.98 million ha-cm) can support a 50% expansion in the current rice irrigated area in Tanzania. Even without irrigation expansion, the 80% SRI can increase rice production by 1.5 million tons annually while enhancing water availability for industrial and environmental uses (e.g., ecological preserves) and help achieve food security in Tanzania and the greater sub-Saharan Africa.

Raised-bed plasticulture is used globally to produce fresh market vegetables, fruits, and other crops. A novel compact bed geometry, designed to improve the system efficiency of plasticulture, was evaluated for its ability to reduce water and other inputs and facilitate the adoption of precision irrigation using savings from reduced input costs. Using measurements and modeling (HYDRUS), precision soil moisture–based irrigation management (SM) and grower-based irrigation management (GR) were evaluated for conventional and compact beds. Similar to previous studies, SM reduced applied irrigation by 20% and deep percolation losses by 30% compared to GR for conventional beds. However, the significant investment needed to buy and maintain modern soil moisture measurement systems is likely to limit the adoption of SM. Compact bed geometries, taller and narrower than conventional beds, can sustain yields while reducing inputs of water, pesticide, fertilizer, fuel, and plastic. Cost savings of $\mathrm{\$}154–\mathrm{\$}789/\mathrm{ha}$ associated with the reduced inputs for compact beds can cover the cost of a soil-moisture sensor network with an automated irrigation system for a typical 65-ha fresh produce farm. Model simulations showed that compact beds with SM reduced irrigation volume by 8%–36% and deep percolation losses by 18%–54% compared to the traditional practice of conventional beds with GR. Compact beds with SM also reduced runoff volume by increasing evaporation by 15%–35%, available soil water storage by 12%–13%, and field infiltration of rainfall by 9%–18%. A basin-wide adoption of compact beds with precision irrigation can help reduce excessive downstream flows and nutrient loads in warmer and ecologically sensitive production regions such as the Everglades and the Chesapeake Bay.