Turnover of minerals and organics in the postharvest herbage of annuals and perennials: Winter wheat and goldenrod

Abstract

Crossing annual cereals, legumes, and oilseeds with wild rhizomatous relatives is used to create perennial lines that fruit over 2–3 seasons. Contrary to annual crops, the year-round vegetation cover should contribute to carbon sequestration, soil formation, and root mineral preservation. Soil erosion, nutrient leaching, and labor expenses may be reduced. While deep-rooted grasses actually inhibit nitrate leaching, advantages in nutrient storage and soil formation are not yet shown. Therefore, the turnover of organics and minerals in the perennial goldenrod was compared with that of winter wheat between blooming and resprouting (28 February) by gravimetry and ICP-MS. From blooming (23 August) to harvest (13 November), goldenrod stalks of 10,070 (given in kg ha−1) lost 23% by dry weight (DW) and released 14.9/9.6/65.7 in NPK and 2193 in water-soluble organics via leaching and root exudation. Apart from a transient rise of 28.8 in N around 13 November, the stubble/rhizome system held CaKMg(N)P stable at a level avoiding metal stress from 23 August to 28 February. Filling seeds in wheat excluded net losses of minerals and organics from anthesis to harvest (23 July). Stubbles (16 cm) and spilt grains of 2890 represented 41.8/2.91/62.5 in NPK and lost 905 in biomass with 25.4/1.8/59.8 in NPK to the soil by 28 February. In wheat-maize rotations, ploughing was avoided until early March. Weeds and seedlings emerged from spilt grains replaced losses in stubble biomass, N, and P but left 40.5 in K unused to the soil. In wheat-wheat rotations, organics and minerals lost by the down-ploughed biomass were replenished by the next-rotation seedlings that left only 18.3 in K to the soil. In summary, off-season goldenrod rhizomes did not store excess minerals. The rate of mineral preservation corresponded with the quantity of the biomass irrespective of its perennial habit. Released water-soluble organics should foster microbial carbon formation and CO2 efflux while soil improving gains in humate C should depend on the lignin content of the decaying annual or perennial biomass. Clues for NPK savings by perennials were not found.