Workpackage 3: Nutrient acquisition and effect on N loss and subsequent crop N

The main objectives of this Workpackage are: 

• Determine the intercrop nitrogen (N) acquisition and N balances as compared to sole crops.

• Determine the effects of intercropping on post-harvest N dynamics in the soil.

• Determine risk of N leaching after intercrops compared to sole crops.

• Determine succeeding crop-N accumulation as influenced by precrop – inter- or sole crop and estimate the economic effects. 

• Determine phosphorous, potassium and sulphur accumulation by intercrops as compared to sole crops.

In order to meet these objectives, the Workpackage is divided in five sub-packages, each of them involving different partners as well as requiring different methodology:  

·         Workpackage 3.1 (Partners 1, 3, 4, 5, 7): In the basic field experiment on spring sown pea-barley row intercropping (described in WP2) all principal contractors will determine the total N acquisition and partitioning of N for harvestable yield in intercrops as compared to sole crops. The partners will determine the dry matter and total Nitrogen in aboveground plant parts at the beginning of flowering stage and at maturity by elemental analysis or Kjeldahl N determination. 

·         Workpackage 3.2 (Partners 1, 2, 3, 4, 5, 7): The soil N-use and symbiotic N₂ fixation by intercrops as compared to sole crops will be determined at all sites of the basic experiments using standard ¹⁵N isotope methodology and cereals as reference crops. ¹⁵N analysis will be carried out by Partner 2 on a grinded sample representative for aboveground plant parts sent by all partners. Partner 4 will include additional sampling for model development (WP6) as well as estimation of soil N use and N₂ fixation in winter pea- winter wheat ICs. 

·          Workpackage 3.3 (Partners 1, 3, 4, 5, 7): The soil N dynamics after harvest of inter- and sole crops is determined by all principal contractors in the basic field experiment for the evaluation of the risk of N leaching. Nitrate and ammonium is determined early and late autumn and spring (immediately before sowing) with the use of standard colorimetric methods. Water balance data will be collected for estimating the leaching risk. Partner 7 will determine soil nitrate and ammonium also after autumn-established pea-barley and fababean-wheat intercrops.

·         Workpackage 3.4 (Partners 1, 3,4, 5, 7): After the basic design two post- harvest treatments are included. All partners will determine total N uptake in a succeeding winter wheat crop after the main crops. The wheat crop is established in the autumn, without and with the supply of 50 kg N ha^-1 in spring as urea N in all treatments so as to determine the residual N effect and the total N is determined at late autumn and maturity. Partner 7 will establish also winter wheat after autumn established pea-barley and fababean-wheat experiments. Partners 1 and 3 will establish a catch crop of grass and clover that is incorporated in spring and followed by spring wheat. The N uptake in clover and grass of the catch crop will be determined before incorporation. 

·         Workpackage 3.5 (Partners 1, 5): Determination of P, K, S by the use of standard photometric methodology and elemental analysis will be performed in one of the intercrops and the sole crops to evaluate alternative mechanisms of intercrop advantages other than improved use of N sources.