Reliance on Biological Nitrogen Fixation Depletes Soil Phosphorus and Potassium Reserves

Abstract

Limited nutrient availability is one of the major challenges in organic farming. Little is known about nutrient budgets of organic farms, the underlying factors or effects on soil fertility. We therefore assessed farm gate nutrient budgets for nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg) and sulfur (S) of 20 organic farms in Germany and analyzed their soil nutri-ent status. In average, the budgets showed a surplus of N (19 kg ha−1), K (5 kg ha−1), S (12 kg ha−1), and Mg (7 kg ha−1), and a deficit of P (−3 kg ha−1). There was, however, high variability between farms (e.g. standard deviation up to ± 36 kg N ha−1), which was mainly explained by different degrees of reliance on biological N fixation (BNF) as N source. When farms obtained more than 60% of their N input through BNF, they had deficits of P (mean −8 kg P ha−1) and K (mean −18 kg K ha−1). Nutrient status of most soils was within the ad-vised corridor, but for P, K and Mg, 10–15% of fields were lower and 45–63% were higher than advised. Extractable soil nutrient contents did not correlate with the nutrient budgets, inputs or outputs. Only extractable soil P increased with increasing P inputs and outputs. Fur-thermore, a decrease in extractable soil P was detected with a prolonged history of organic farming, indicating a risk of soil P mining in organic farming systems. In conclusion, the study revealed nutrient imbalances in organic farming and pointed to P and K scarcity as a major challenge for organic farms with high reliance on BNF in the long term.

Application of Some Organic Farming Methods to Enhancement The Growth and Production of Green Onion تطبيق بعض أساليب الزراعة العضوية لتعزيز نمو وإنتاج البصل الأخضر

“…The increment of NPK percentage and uptake in inoculated plants may be due to the positive role of inoculation with PGPR strains in improving the availability and absorption of these nutrients. These results are in agreement with those obtained by Reimer et al, (2020) who reported that the use of PGPR strains as bioinoculants would improve the supply of nutrients in the soil, decrease the use of artificial fertilizers, reduce emissions, and encourage sustainable agriculture. Effects on growth characteristics Data in Table ( 11) showed significant increases in plant height, leaves number and dry weight of onion plant that inoculated with various PGPR strains compared with uninoculated one.…”

The State of Play of Copper, Mineral Oil, External Nutrient Input, Anthelmintics, Antibiotics and Vitamin Usage and Available Reduction Strategies in Organic Farming across Europe

“…As for the external nutrient input usage, results showed that the majority of surveyed farms had a positive N budget, while for K and P, on average they had slight deficits, although on some farms deficits were pronounced and a risk of soil mining was identified. In a study analysing the German farms [106] authors found that reliance on biological nitrogen fixation depletes soil phosphorus and potassium reserves. Furthermore, soils were collected from all the German farms and a decrease in extractable soil P was detected from soils with a prolonged history of organic farming, indicating a long-term risk of soil P mining in organic farming systems.…”

Comparative Analysis of Soil Fertility, Productivity, and Sustainability of Organic Farming in Central Europe—Part 2: Cultivation Systems with Different Intensities of Fertilization and Legume N2 Fixation as well as Perspectives for Future Development

“…[43] Federal state of Saxony, 32 farms, 1200 arable and grassland plots; -ref. [44] 20 farms; -ref. [45] 82 farms; -ref.…”

“…It can be concluded from these experimental data that the longer these deficit cropping conditions with clearly negative nutrient balances persist and the higher the yield level as a result of N-emphasized organic fertilization or an elevated legume cultivation in the crop rotations, respectively, the more the soil is depleted in basic nutrients. For example, very low soil P and K contents are often found in older organic farms and under intensified legume cultivation [11,18,44,85].…”

“…In several studies from Germany and other European countries, higher values than 160 kg N ha −1 supply via organic fertilizers, as well as N balances of more than 100 kg N ha −1 year −1 , were determined in individual farms [18,44,48,50,95,112,113]. According to Haas and Deittert [20] (see also [53]), N balances of up to 85 kg N ha −1 year −1 were also calculated in intensive dairy farms, where milk yields up to 9000 kg cow −1 year −1 are common, by purchasing high amounts of fodder concentrates and other special feeds.…”