LAI, defined as the green leaf area per ground area is closely related to FAPAR, the fraction of radiation in the 400−700 nm spectrum that is absorbed by green elements of the vegetation canopy and thus available for photosynthetic activity by plants. Finally, the LSWI uses the shortwave infrared (SWIR) and near infrared (NIR) bands that are strongly absorbed by liquid water to provide a measure of the total amount of liquid water in vegetation and its soil background that will be relevant to check if excessive extraction of soil water by deep-rooted sunflowers is a plausible be mechanism for sunflower’s negative impact on successor crops’ yield as observed above.

As illustrated in table 6, crop rotation characteristics for maize based on data from 3 seasons explain 30% to 40% of the variation in vegetation indices. Results are consistent with what was obtained for yield in that sunflower is by far the worst predecessor crop for maize with an outsized effect (compared to that of other crops) especially on water availability as measured by the LSWI. The relatively better performance of other <mark>crops as compared to cereals may be attributable to their positive impact (compared to soybean as omitted category with which they may also share N-fixing properties) on water balances both in dry and in average</mark> years. Insignificant differences in terms of water balances between maize and soybean (with a negative <mark>effect only for maize being cultivated three times in a row) may also partly explain that the negative impact of continued maize cultivation is relative limited.</mark> Results for vegetation indices for areas covered with soybean in table 7 reinforce the notion of soybean being a better successor crop than maize for other crops (where coefficients are positive and significant for <mark>all four indices) and itself in dry seasons (all indices for 2016/17 are positive and significant with the</mark> exception of the positive and insignificant LSWI). Cereals as predecessor crop have a positive impact on LSWI as they extract limited amounts of water but a negative one on LAI and, in 2018, FAPAR and EVI. The estimated magnitude of this effect on FAPAR and EVI (and to a lesser extent LAI), though remains modest compared to the negative and significant effect of sunflower not only on vegetation indices, likely a result of high susceptibility of soybean and sunflower (but not maize) to stem rot and on water availability, a result of sunflowers’ deep root system that reduces moisture availability for successor crops.

Table 8 illustrates that, consistent with yield results and negative impacts as a predecessor for other crops as documented above, sunflower is also a bad successor to itself . Coefficients on the share of area where the crop is grown twice or thrice in a row for all four indices considered are negative, significant at 1%, and in most cases much larger than those for cereals, as the predecessor crop with the second most negative effect. Estimated impacts of growing sunflower thrice are statistically significantly larger than those of growing it twice in a row with the difference particularly large for the LSWI where the size of the negative impact of a triple sunflower rotation is estimated to be more than double that of a double sunflower rotation. Interestingly, preceding sunflower with other crops is estimated to have a positive effect (compared to 13