There are many benefits to the sugarcane crop of le- guminous plants rows in rotation in maize; these include the recycling of nutrients taken up from deep soil layers by the rotational crop, which may prevent or decrease leaching losses, and the addition of N from biological fixation. Leguminous plants can accumulate over 5 t·ha−1 of dry mass during a short period of time during the summer and take up large amounts of N and K. Most of this N comes from the association of legumes with rhizobia. In this way crop rotation with legumes can replace partially or totally N mineral fertilization of maize. This study evaluated and characterized the green manure biomass production, N balance, the biomass mineralization of leguminous green manure and common beans residues in succession with corn and rotation with sugarcane and their effect in the soil. Their effect on stalk and sugar yield on sugarcane cv.

IAC 87-3396 grown subsequently was also studied. As observed in Figure 1, differences occurred between the total soil N amount and concentration that came from the green fertilizer aerial part over time. The aerial part contribution was on average 16.3% compared with 3.5% from roots, indicating that the aerial part participation was four times greater larger than that of the roots, reflecting the greater amount added from the aerial part. Over time the variable described a quadratic curve with the largest contribution at 20 DAE decreasing afterwards to 60 DAE and rising again 100 DAE again, the same was not verified in roots. These results are due, largely, to the uptake of the N that was incorporated by the corn from the green manure where the data described a quadratic curve, but contrary to what was described in Figure 1, with the highest N uptake at 60 DAE sampling and a decrease from that point to 100 DAE. Observed too the constant releasing nitrogen from the roots. In Table 8 the mean data of % NSDGM are observed as a function of sampling time and of the legume plant part that was incorporated, for Eutrudox and Paleudalf soils.

The contribution of the legume nitrogen in the Paleudalf soil, with the N supply from the velvet bean being was higher. Four velvet bean, out of the 35%, the aerial part con- tributes with 27.8% and the roots only 7.2% in the Paleudalf soil, higher than that in Eutrudox where the contribution of the aerial part that was 11.0% and 2.8% respectively for aerial part and roots. These results are consistent with the higher mineralization rate of the organic matter in soils with less clay, as observed above. The lower C/N ratio in velvet bean aerial part as well as in roots is lower than in sunn hemp favoring its higher mineralization in both soils . The levels of mineral Nin the soil were higher until 40 DAE in the Velvet bean treat- ment followed by the sunn hemp and finally the check. It can be observed that beyond 60 DAE the values were low, smaller than 1.6 mg·kg−1, without differences among treatments . For the sunn hemp, there were differences among the times, with a decline in the green manure contribution to the soil mineral N. However, this did not happen with the velvet bean treatment indicating that, besides the largest contribution of the green manure plants to the soil mineral N, there was also greater mineralization, since the test-plant kept on taking up mineral N from the soil. It is observed in the Table 10 that the Paleudalf had higher mineral N concentration than the Eutrudox soil regardless of the soil sampling time. These results are in agreement with those obtained by who found higher organic matter mineralization in low-N soils.

In that study, the authors observed that 13% of the mineral nitrogen originated from the added plant residue, compared to 5% in the high-N soil. Jans-Hammermeister et al.observed N mineralization rates in two soils after addition of pea aerial part and verified that the higher rates were associated with soils that had lower clay percentages. Similar results were also verified by and other authors cited by. It can be noticed that the percentage of plant nitrogen from the green manure was practically constant during the experiment. This fact is not usually observed when mineral fertilizer or another soluble N source is applied, where a greater proportion of the nitrogen use from the fertilizer happens initially with a reduction in these values in subsequent stages . The amounts of N in the aerial part of the corn plant that was derived from the green fertilizer, for the two legume species, as a function of time can be observed in Table 12. No differences among treatments were observed until 40 DAE, however at 60 DAE the Velvet bean turned out to be the major N supplier to the corn plant, probably due to the largest N concentration in that green manure, and its lower C/N ratio. Despite the higher amounts of N accumulated in the sunn hemp treatments, at the 60 and 100 DAE sampling dates the amount of N from the green manures was higher for the black mucuna, at any given same date, indicating the al for N supply potential of this plant. The reduction in the amounts accumulated at the end of the cycle followed the same pattern verified for the total nitrogen and is likely due to the loss of nitrogenous compounds from mature or pre-senescence leaves, which can happen next to the transpiratory strem.