Sustainable Soil Management Is More than What and How Crops Are Grown - Principles of Sustainable Soil Management in Agroecosystems - page 373

and plant root systems are managed. Also, high water productivities under good soil
moisture supply are possible only when plant nutrition is adequate. Similarly, no
amount of fertilizer application and use of modern varieties will improve water use
efficiency and water productivity if the soil has a hardpan in the rooting zone or if the
soil has little organic matter to build and maintain good soil structure and porosity
for maximum moisture storage and root growth. Equally, without the maintenance
of good water infiltration and without soil cover to minimize evaporation from the
soil surface, it is not possible to fully optimize and maximize water use and water
productivity. Another example is the above-described SRI system: the interrelation
of the soil characteristics, providing an optimal rooting environment, allowing dif-
ferent plant spacings, which can lead to different phenotypic plant development as
compared to conventional practices.
Thus, agricultural soils maintained in good health and quality will offer the pos-
sibility of making optimum soil moisture and nutrients available for crop produc-
tion over the period of the crops' development and of optimal input use efficiencies
through good agronomic manipulation or good crop management. However, good
crop management is not an independent variable but a function of how sustainably
the production system as a whole is being managed in order to maintain or intensify
production while harnessing the desired ecosystem services.
14.6.2 S uStainaBle S oil m anagement with i intercroPPing aS
an a lternative in P ermanent n o -t ill S yStemS
In tropical regions, the high rate of organic material decomposition associated with
warm and wet climate conditions is a challenge to meeting the prerequisite of per-
manent soil cover required by CA. Most of the straw input, even when maintained
on the soil surface, is decomposed in 20 to 60 days according to the C/N ratio, N
content, and lignin content of plant material. This fact results in bare soil and risk of
soil erosion and degradation. Also, the weed infestation, depletion of SOM, nutrient
leaching, and soil compaction are processes associated with bare soils in the tropics.
The decrease in soil productivity as a consequence of deterioration in soil quality is
a threat to permanent no-till in the tropics. In order to overcome this situation, the
farmers try to increase the amount of crop residue input and select pearl millet as a
grass-type cover crop in order to maintain soil cover for a longer period.
The use of perennial forage plants, such as Brachiaria , intercropped with grain
crops is a promising alternative to providing greater soil sustainability in no-till sys-
tems in tropical Brazil. The large-scale success of Brachiaria in strengthening soil
and production sustainability in Brazil provides a specific example of why partici-
pating crops in no-till cropping systems are important to both sustainable soil man-
agement as well as sustainable production. There are many species of Brachiaria
that were introduced from Africa into Central Brazil in the early 1960s, the most
common being Brachiaria brizantha , B. decumbens , and B. ruziziensis (Landers
2007). The best Brachiaria intercrop alternative with corn has been investigated
with N fertilization. The straw of Brachiaria in combination with corn stalks can
input as much as 17 tons of dry mass per hectare and provide soil cover for more than
100 days. Brachiaria pastures on cerrado soils can last up to 5 years and can raise