The role of cover crops in irrigated systems: water balance, nitrate leaching and soil mineral nitrogen accumulation

Published source details Gabriel J.L., Muñoz-Carpena R. & Quemada M. (2012) The role of cover crops in irrigated systems: water balance, nitrate leaching and soil mineral nitrogen accumulation. Agriculture, Ecosystems & Environment, 155, 50-61.
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This study is summarised as evidence for the following.

	Action	Category
	Water: Grow cover crops in arable fields Action Link
	Soil: Grow cover crops in arable fields Action Link

Water: Grow cover crops in arable fields

A replicated, randomized, controlled study in 2006–2009 in an irrigated maize field in the Tajo river basin, near Madrid, Spain, found that less nitrate was leached from soils with winter cover crops, compared to fallows. More water was used by cover crops, compared to fallows, but less water was lost through drainage and evaporation. Water use: More water was used by cover crops, compared to fallows (transpiration: 31–117 vs 0 mm). Water availability: Less water was lost through drainage from plots with cover crops, compared to fallows, in six of eight comparisons (47–301 vs 106–314 mm), and less water was lost through evaporation, in all comparisons (31–79 vs 51–101 mm). Similar amounts of water were lost as runoff from plots with cover crops or fallows (data not reported). Nutrients: Less nitrate was leached from soils with cover crops, compared to fallows, in five of eight comparisons during the cover-cropping seasons (13–36 vs 45–147 kg N-NO₃/ha), and two of six comparisons during the maize-growing seasons (12–30 vs 42). Implementation options: Less nitrate was leached from soils that were cover cropped with barley, compared to vetch (129 vs 245 kg N-NO₃/ha cumulative, in 2006–2009). Less water was lost through drainage from plots that were cover cropped with barley, compared to vetch, in two of four comparisons (47–234 vs 60–301 mm), but barley used more water than vetch, in three of four comparisons (transpiration: 63–117 vs 31–108 mm). Less water was lost through evaporation from plots that were cover cropped with barley, compared to vetch, in one of four comparisons (60 vs 79 mm). Methods: There were four plots (12 x 12 m plots) for each of two treatments (barley or vetch, as winter cover crops) and there were four control plots (fallow). Cover crops were sown in October 2006–2009 and maize was sown in April 2007–2009. The maize was irrigated (sprinklers) and fertilized (210 kg N/ha, split into two applications, 120 kg P/ha, and 120 kg K/ha). Soil water content was measured every hour with capacitance probes (10–130 cm depth, three probes/plot, after the cover crops and after the harvest), and nitrate in soil water was measured with ceramic suction cups (buried at 122–124 cm depth, 1 µm pore size). Water balance and nitrate leaching were calculated using the WAVE model.
Soil: Grow cover crops in arable fields

A replicated, randomized, controlled study in 2006–2009 in an irrigated maize field in the Tajo river basin, near Madrid, Spain, found that winter cover crops had inconsistent effects on nitrogen. Nutrients: Less nitrogen was found in soils that were cover cropped with barley, compared to fallows, in one of four comparisons (31 vs 156 kg N/ha). More nitrogen was found in soils that were cover cropped with vetch, compared to fallows, in one of four comparisons (113 vs 43 kg N/ha). Implementation options: Less nitrogen was found in soils that were cover cropped with barley, compared to vetch, in two of four comparisons during the cover-cropping seasons (45–49 vs 113–184 kg N/ha), and one of three comparisons during the maize-growing seasons (99 vs 253). Methods: There were four plots (12 x 12 m plots) for each of two treatments (barley or vetch, as winter cover crops) and there were four control plots (fallow). Cover crops were sown in October 2006–2009 and maize was sown in April 2007–2009. The maize was irrigated (sprinklers) and fertilized (210 kg N/ha, split into two applications, 120 kg P/ha, and 120 kg K/ha). Soil water content was measured every hour with capacitance probes (10–130 cm depth, three probes/plot, after the cover crops and after the harvest), and nitrate in soil water was measured with ceramic suction cups (buried at 122–124 cm depth, 1 µm pore size).