Potassium balances for arable soils in southern England 1986–1999

Abstract

Abstract. The behaviour of potassium (K) in a range of arable soils was examined by plotting the change in exchangeable K of the topsoil (Δ Kex) at the end of a 3–5 year period against the K balance over the same period (fertilizer K applied minus offtake in crops, estimated from farmers' records of yield and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops MAFF 2000) are valid averages, 10–50% of Δ Kex was explained by the balance, relationships being stronger on shallow/stony soils. Excess fertilizer tended to increase Kex and reduced fertilization decreased it, requiring between 1.2 and 5.4 kg K ha−1 for each mg L−1Δ Kex. However, merely to prevent Kex falling required an extra 20 kg K ha−1 yr−1 fertilizer on Chalk soils and soils formed in the overlying Tertiary and Quaternary deposits, despite clay contents >18%. Whereas, on older geological materials, medium soils needed no extra K and clays gained 17 kg K ha−1 yr−1. It is unlikely that the apparent losses on some soil types are anomalies due to greater crop K contents. Theory and the literature suggest leaching from the topsoil as a major factor; accumulation in the subsoil was not measured. Recommendations for K fertilization of UK soils might be improved by including loss or gain corrections for certain soil types.

N, P, and K Budgets and Changes in Selected Topsoil Nutrients over 10 Years in a Long-Term Experiment with Conventional and Organic Crop Rotations

“…The literature appears inconclusive, however, when it comes to K-budgets for conventional arable cropping systems. This was well illustrated by Heming [44], who studied a large number of fields in southern England, reporting K budgets (K applied in fertilizer minus K in crop) ranging from −40 to +70 kg K ha −1 yr −1 . The organic arable system OA had a calculated K-deficit.…”

Potassium release and fixation as a function of fertilizer application rate and soil parent material

“…Because many crops tend to consume more K than needed for optimal growth, mineralogical and chemical factors in the soil are also likely to affect the release of non-exchangeable K. For instance, Heming (2004), in his investigation of a large number of soils and K balances in southern England, was able to divide his material into (i) brown rendzinas that required excess fertilizer, 22 kg ha − 1 yr − 1 over off-take, to remain at a constant concentration of K ex , (ii) soils that remained at constant K ex if fertilized to replacement of K off-take, and (iii) calcareous clays able to deliver on average 15 kg ha − 1 yr − 1 . Using 'routine' soil parameters, to predict the rates of such processes, is a major challenge in soil management.…”

“…Table 2 Details on rotation systems, manure, and fertilizer application rates of the soil fertility experiments; for more information, see Carlgren and Mattsson (2001) From a practical point of view, several approaches exist to estimate the release of non-exchangeable K under agricultural conditions. Jouany et al (1996) and Heming (2004) used fields receiving K fertilizer at varying application rates, to determine the K balance required to maintain the pool of exchangeable K constant with time. On the one hand, if the soil could support a negative balance, then the soil was said to deliver the corresponding amount of K by weathering.…”

A landscape-scale experiment on the changes in available potassium over a winter wheat cropping season

“…Based on this, Heming (2004) stated that K-fertilizer recommendations should be based on soil type, in particular the potassium-release behaviour of the soil. In some soils relatively large amounts of non-exchangeable K are released over a period of time due to weathering of clay minerals.…”

“…The management of soil potassium Heming (2004) examined the potassium balances in the soil of southern England. He plotted the change in exchangeable potassium (ΔK ex ) against the K-balance (K-fertilizer applied − K-crop offtake) from 1300 fields over a 3-6 year period.…”