Harald Schmid

The use of the ingrowth core method for measuring root production of arable crops - influence of soil conditions inside the ingrowth core on root growth.

The ingrowth core method can be used to measure root gross growth (i.e. root production). A mesh bag filled with root free soil is buried into the root zone. After about 14 days, the bag is pulled out and root length inside the core can be determined. An objection against this method is the inability to obtain the same soil conditions inside the bag as outside, which can result in different root growth pattern in the ingrowth core compared to the bulk soil. To study this, mesh bags were buried in a stand of oilseed rape and were filled with soil at different nitrate, phosphate, moisture, and bulk density levels. Results showed that root growth was only influenced by a high nitrate content and a high soil density in the cores, which resulted in higher and lower root length densities (RLD), respectively. In a long-term ingrowth experiment similar root length densities in the cores and in the bulk soil were measured, indicating that there were no root growth enhancing or impeding conditions inside the ingrowth cores. The conclusion is drawn, that the ingrowth core method gives reliable results, provided the N content and the soil density inside the bags are comparable to the bulk soil.

The use of the ingrowth core method for measuring root production of arable crops – influence of soil and root disturbance during installation of the bags on root ingrowth into the cores

Abstract To measure root production by the ingrowth core method mesh bags filled with root-free soil are buried into the root zone of plants. After a time period which should be shorter than the lifespan of the roots the mesh bags are pulled out and root length inside the cores is determined. A major objection against this method is a possible alteration of root growth pattern induced by root injuries or soil disturbances that occur during the insertion of the mesh bags into the soil. Root length density (RLD) in the mesh bags was between 0.7 and 5.0 cm cm−3 after 14 days of ingrowth of wheat or barley roots depending on soil type or plant age. RLD in the bulk soil next to the mesh bags was between 7.7 and 14.8 cm cm−3 in the 0–30 cm soil depth. Different time periods between inserting the mesh bags and opening them for root ingrowth in which the installation disturbance could settle, had no effect on RLD in the ingrowth cores. There were also no differences in RLD in the direct vicinity around the ingrowth cores and the bulk soil, which was tested by counting roots at profile walls adjacent to the mesh bags and by taking soil samples around the cores with an auger. The conclusion of these results was that no alteration of root growth pattern occurred in or around the ingrowth cores due to the installation of the mesh bags. However, further investigations are necessary to validate this method as a reliable and easy field method for measuring root growth.

Seasonal development of biomass yield in grass–legume mixtures on different soils and development of above- and belowground organs of Medicago sativa

Grass–legume mixtures are suitable for crop rotations under organic farming. Little attention has been paid to seasonal development of mixtures with alfalfa under field conditions. We investigated the effects of site and cut on herbage and belowground biomass yields of grass–legume mixture and on above- and belowground traits of Medicago sativa. Six sites in southern Germany were monitored during 2011. Dry matter herbage yield ranged from 9 to 16 t ha−1. The total herbage yield of three cuts per year decreased from 45% to 36% and 19%. The belowground biomass in the upper 30 cm soil layer ranged from 1.7 to 3.8 t ha−1.There was no seasonal trend. Diameter of the root neck and maximum order of branching of alfalfa increased during the season. The number of nodules per plant decreased from 9.5–17.0 in May to 7.5–13.0 in August. By the last cut, roots with larger diameter created smaller nodules. More branched roots created more nodules independent of their shape. Thinner roots have more active nodules. Plant height, number of stems and inflorescences per plant were higher in July and August than in May. In conclusion, a holistic analysis including above- and belowground traits should be used for the evaluation of fodder crops.

Root‐and‐shoot growth and yield of different grass–clover mixtures

Abstract The effect of different grass–clover mixtures on yield, root biomass, root length and the symbiotically fixed N quantity was investigated in a two‐factorial field experiment at a location in Freising (Germany). Three grass–clover mixtures with different compositions were tested in two different management systems (various harvest and mulching): a standard mixture (SM) consisting of 40% legumes and 60% grass; a multi‐species legume–grass mixture suitable for forage use (FM) and a mixture adapted for green manure (GM) with a high share of legumes (70%) and herbs (5%). The botanical composition shifted in favour of the amount of grass in mulching variants. Certain herbs managed to do well in the mixtures despite intensive management with four cuts. Grass–clover mixtures with herbs and legumes achieved high shoot yields (15.9–16.5 t ha−1). Due to its lower share of grass, GM showed the smallest root length (95 km m−2). FM and SM achieved a length of 130 km m−2 (depth: 0–30 cm). The measurement of root biomass gave high dry matter yields (FM 8.1 t ha−1, GM 6.5 t ha−1, SM 5.3 t ha−1). N uptake depended on the share of legumes and on the management system. The amount of symbiotically fixed nitrogen that accumulated in shoots and roots was about 90 kg N ha−1 (SM), 290 kg N ha−1 (FM) and 340 kg N ha−1 (GM). The C input was increased by mulching systems and a high root biomass. FM has shown possibilities for optimizing grass–clover mixtures with respect to the root parameters, effects on soil fertility and increasing C input without a decline in yield. The rooting patterns can be used to compose grass–clover mixtures with a higher root biomass and root penetration.

Wurzelerneuerung bei Wintergerste und ihre Bedeutung für die P-Versorgung

A part of the root system dies already during plant development (root mortality) and is replaced by new root growth (gross growth). Therefore, root measurement using auger sampling methods gives information only about the net size of a root system. In case of winter barley root, gross growth between 1 April and 18 June was more than twice the net size of the root system and even greater at P shortage. New roots can exploit undepleted soil and therefore average uptake rates of a root system with a high turnover should be greater than of a root system with a low turnover. Thus, model calculations based on gross root growth of barley resulted in a 4–17 % higher uptake than based on the net development of the barley root system. Measured uptake was still higher, so a high root turnover is not the single strategy to gain more phosphate at P shortage.

Humus, nitrogen and energy balances, and greenhouse gas emissions in a long-term field experiment with compost compared with mineral fertilisation

Compost fertilisation is one way to close material cycles for organic matter and plant nutrients and to increase soil organic matter content. In this study, humus, nitrogen (N) and energy balances, and greenhouse gas (GHG) emissions were calculated for a 14-year field experiment using the model software REPRO. Humus balances showed that compost fertilisation at a rate of 8 t/ha.year resulted in a positive balance of 115 kg carbon (C)/ha.year. With 14 and 20 t/ha.year of compost, respectively, humus accumulated at rates of 558 and 1021 kg C/ha.year. With mineral fertilisation at rates of 29–62 kg N/ha.year, balances were moderately negative (–169 to –227 kg C/ha.year), and a clear humus deficit of –457 kg C/ha.year showed in the unfertilised control. Compared with measured soil organic C (SOC) data, REPRO predicted SOC contents fairly well with the exception of the treatments with high compost rates, where SOC contents were overestimated by REPRO. GHG balances calculated with soil C sequestration on the basis of humus balances, and on the basis of soil analyses, indicated negative GHG emissions with medium and high compost rates. Mineral fertilisation yielded net GHG emissions of ~2000 kg CO2-eq/ha.year. The findings underline that compost fertilisation holds potential for C sequestration and for the reduction of GHG emissions, even though this potential is bound to level off with increasing soil C saturation.