Nutrient uptake in the plants

In this study, the general trend observed with respect to NPK (Nitrogen, Phosphorous, Potassium) nutrient uptake was a positive effect due to intercropping in the rice plants cultivated with SRI methods.

Nitrogen

The nitrogen content in the mature leaves was found to be higher in SRI+I plants, indicating a higher nitrogen uptake. The nitrogen content was found to be 0.69% in SRI+I leaves, 0.64% in SRI leaves, and 0.58% in FR leaves (Figure 30-31). This can be attributed to the effects of nitrogen-fixing legumes intercropped with the rice on the soil, which include increased mycorrhiza formation and colonization³⁵⁷. A higher N-uptake is a sign of better growth of plants and a higher yield potential. The higher nitrogen uptake, and nutrient uptake in general, in case of SRI as compared to CFR has been attributed to the greater biomass and vigour of roots under SRI management^358,359. The differences in nitrogen uptake were consistent across all replications of the three treatments and statistically significant (p < 0.05).

27

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RESULTS AND DISCUSSIONS

Figure 30. Nutrient uptake in flooded rice, SRI, and SRI with intercropping in the first experiment (2017 GH)

Figure 31. Nutrient uptake in SRI and different configurations of SRI with intercropping in the third experiment (2018b GH);

I9: intercropping at 9 DAT; I35: intercropping at 35 DAT; IS: intercropping as strip cropping at 9 DAT

Potassium

The potassium content in SRI+I rice plants was also recorded to be higher than in the SRI plants, indicating a higher phosphorus uptake in the rice intercropped with beans, although it was not very different than that of CFR treatment. The potassium content was found to be 2.75% in SRI+I leaves, 2.43% in SRI leaves, and 2.80% in FR leaves (Figure 32-33). In this case as well, the trend was similar across the three replications, with SRI+I recording higher phosphorus-uptake than unmodified SRI (p < 0.05) although there was no significant difference from FR practice. The slightly higher uptake of potassium in flooded rice observed in this study follows the trend observed by Beyrouty et al. (1994), who also observed that potassium uptake did not limit growth when compared between flooded and intermittent irrigation³⁶⁰.

0.58

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RESULTS AND DISCUSSIONS

Figure 32. Nutrient uptake in flooded rice, SRI, and SRI with intercropping in the first experiment (2017 GH)

Figure 33. Nutrient uptake in SRI and different configurations of SRI with intercropping in the third experiment (2018b GH);

I9: intercropping at 9 DAT; I35: intercropping at 35 DAT; IS: intercropping as strip cropping at 9 DAT

Phosphorus

The phosphorus uptake in SRI+I was also higher than with the other two treatments, seen from the significantly higher phosphorus concentration in mature leaves. The phosphorus content was found to be 0.33% in SRI+I leaves, 0.25% in SRI leaves, and 0.22% in FR leaves (Figure 34-35). The phosphorus uptake was significantly higher in SRI+I treatment than in the other two treatments (p < 0.05). The higher uptake of Phosphorous in SRI and SRI+I can be attributed to vigorous and early root establishment as pointed out by Jogi et al.³⁶¹. Phosphorous acquisition has been described as a limiting factor in plant growth and phosphorous is an important

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RESULTS AND DISCUSSIONS

Figure 34. Nutrient uptake in flooded rice, SRI, and SRI with intercropping in the first experiment (2017 GH)

Figure 35. Nutrient uptake in SRI and different configurations of SRI with intercropping in the third experiment (2018b GH);

I9: intercropping at 9 DAT; I35: intercropping at 35 DAT; IS: intercropping as strip cropping at 9 DAT

The individual values of nitrogen, phosphorus and potassium uptake in the case of SRI+I were significantly higher than in SRI (p < 0.05). The contribution of legume intercropping to the NPK nutrient uptake in upland dry rice plants has been attributed to the nodule-forming ability of the legume plants as well as to vesicular-arbuscular mycorrhizae³⁶⁵. It has been reported that in cereal and legume intercropping, mycorrhizae formation is increased, leading to improved nodulation and hence to increased acquisition of N and P³⁵⁷.

0.22

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RESULTS AND DISCUSSIONS

Soil Organic Matter

Figure 36. A comparison of the final organic matter in soil in SRI and intercropping pots (GH 2018b)

The soil organic matter content was also measured at the end of experiments in GH 2018b batch. The organic content was found to be slightly higher in case of intercropped SRI than in SRI, as shown in Figure 36. Any improvements in the organic content of soil can lead to improvement in different plant growth supporting characteristics of the soil^366,367.

4.2.3. Chlorophyll content

The content of both chlorophyll-a and chlorophyll-b was considerably higher in SRI+I leaves than in the leaves of either SRI or FR. The measured chlorophyll-a and chlorophyll-b contents were 12.85 and 3.87 µg/g; 9.15 and 2.83 µg/g; 9.34 and 3.03 µg/g for SRI+I, SRI and FR treatments, respectively (Figure 37 and Figure 38).

11.25

10.00 10.23

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

Different treatments

Soil Organic Matter (%)

Initial Final-SRI Final-I35

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RESULTS AND DISCUSSIONS

Figure 37. A comparison of the chlorophyll content (a and b) in the leaves in the first experiment (GH 2017)

Figure 38. A comparison of the chlorophyll content (a and b) in the leaves in the third experiment, featuring different intercropping configurations (2018b)

It can be seen from the data that intercropping had a strong positive impact on the chlorophyll content of the rice plant leaves under SRI. The observed data suggests that SRI and intercropping improve the chlorophyll content of the leaves (Figure 39). Chlorophyll content in crops has been suggested to be linked to increases in biomass production and grain yield in the crops³⁶⁸. Based on these numbers, it can be expected that intercropping leads to an improved performance of the rice crop.

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Figure 39. A comparison of the total chlorophyll content in the leaves at different stages in the different intercropping configurations (GH2018b)